@article{lima pilon_cava_hoffmann_abreu_rossatto_durigan_2022, title={Effects and response of the Cerrado ground-layer to frost along the canopy cover gradient}, ISSN={["1432-1939"]}, DOI={10.1007/s00442-022-05259-9}, journal={OECOLOGIA}, author={Lima Pilon, Natashi A. and Cava, Mario G. B. and Hoffmann, William A. and Abreu, Rodolfo C. R. and Rossatto, Davi R. and Durigan, Giselda}, year={2022}, month={Sep} }
 @article{flake_honda_pilon_hoffmann_durigan_2022, title={Not all trees can make a forest: Tree species composition and competition control forest encroachment in a tropical savanna}, ISSN={["1365-2745"]}, DOI={10.1111/1365-2745.13820}, abstractNote={en}, journal={JOURNAL OF ECOLOGY}, author={Flake, Samuel W. and Honda, Eliane A. and Pilon, Natashi A. L. and Hoffmann, William A. and Durigan, Giselda}, year={2022}, month={Jan} }
 @article{wall_hohmann_just_hoffmann_2021, title={Characterizing past fire occurrence in longleaf pine ecosystems with the Mid-Infrared Burn Index and a Random Forest classifier}, volume={500}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2021.119635}, abstractNote={Prior to European settlement the longleaf pine (Pinus palustris) ecosystem covered over 92 million hectares in the southeastern United States. Historically, fire was an important driver of species composition in the longleaf pine ecosystem, but fire exclusion since the early 20th century has led to the degradation of longleaf pine communities and has had a detrimental effect on the large number of rare and endemic species found within this system. Thus, accurate estimates of fire history are important for better informed management of longleaf pine communities. Recently, satellite imagery has been used to identify burned areas. However, results have been inconsistent across physiographic regions and vegetation types (e.g. wetlands under high canopy). We developed a model using Landsat satellite imagery, coupled with a Random Forest (RF) machine learning algorithm, to identify burned areas and estimate the fire history from 1991 to 2019 for Fort Bragg, NC, one of the largest contiguous areas of longleaf pine ecosystem remaining. We calculated six spectral indices from the Landsat band values, including the Mid-Infrared Burn Index (MIRBI) and the change in MIRBI through time (ΔMIRBI), and used them as predictors in our RF model. We used the developed RF model to estimate the fire history for all known populations of 24 rare upland and wetland plant species found on Fort Bragg. We compared our results to a recent continental U.S. fire occurrence dataset, as well as the prescribed fire records from Fort Bragg. The overall AUC (area under the curve) for our RF model (0.74) compared favorably to the continental U.S. dataset results for Fort Bragg (0.69), and was able to capture the reduced fire frequency in wetlands. The most important predictor in our RF model was ΔMIRBI. Depending on the model, individual plant species were estimated to have experienced significant differences in fire frequency relative to the prescribed fire records. For our RF model, we estimated that 50% of wetland and 25% of upland species experienced a lower fire frequency relative to that represented in the prescribed fire records. The burn probability and classification tool generated in this paper provides land managers in the southeastern U.S. with a novel approach for accurately identifying burned areas and estimating local fire frequency across landscapes.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Wall, Wade A. and Hohmann, Matthew G. and Just, Michael G. and Hoffmann, William A.}, year={2021}, month={Nov} }
 @article{pellegrini_refsland_averill_terrer_staver_brockway_caprio_clatterbuck_coetsee_haywood_et al._2021, title={Decadal changes in fire frequencies shift tree communities and functional traits}, volume={5}, ISSN={["2397-334X"]}, DOI={10.1038/s41559-021-01401-7}, abstractNote={Global change has resulted in chronic shifts in fire regimes. Variability in the sensitivity of tree communities to multi-decadal changes in fire regimes is critical to anticipating shifts in ecosystem structure and function, yet remains poorly understood. Here, we address the overall effects of fire on tree communities and the factors controlling their sensitivity in 29 sites that experienced multi-decadal alterations in fire frequencies in savanna and forest ecosystems across tropical and temperate regions. Fire had a strong overall effect on tree communities, with an average fire frequency (one fire every three years) reducing stem density by 48% and basal area by 53% after 50 years, relative to unburned plots. The largest changes occurred in savanna ecosystems and in sites with strong wet seasons or strong dry seasons, pointing to fire characteristics and species composition as important. Analyses of functional traits highlighted the impact of fire-driven changes in soil nutrients because frequent burning favoured trees with low biomass nitrogen and phosphorus content, and with more efficient nitrogen acquisition through ectomycorrhizal symbioses. Taken together, the response of trees to altered fire frequencies depends both on climatic and vegetation determinants of fire behaviour and tree growth, and the coupling between fire-driven nutrient losses and plant traits.}, number={4}, journal={NATURE ECOLOGY & EVOLUTION}, author={Pellegrini, Adam F. A. and Refsland, Tyler and Averill, Colin and Terrer, Cesar and Staver, A. Carla and Brockway, Dale G. and Caprio, Anthony and Clatterbuck, Wayne and Coetsee, Corli and Haywood, James D. and et al.}, year={2021}, month={Apr}, pages={504-+} }
 @article{abreu_durigan_melo_pilon_hoffmann_2021, title={Facilitation by isolated trees triggers woody encroachment and a biome shift at the savanna-forest transition}, ISSN={["1365-2664"]}, DOI={10.1111/1365-2664.13994}, abstractNote={Data available via the Dryad Digital Repository https://doi.org/10.5061/dryad.1c59zw3w0 (Abreu et al., 2021). Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, journal={JOURNAL OF APPLIED ECOLOGY}, author={Abreu, Rodolfo C. R. and Durigan, Giselda and Melo, Antonio C. G. and Pilon, Natashi A. L. and Hoffmann, William A.}, year={2021}, month={Aug} }
 @article{scalon_rossatto_oliveras_miatto_gray_chaves bicalho domingos_brum_carlucci_hoffmann_marimon-junior_et al._2021, title={Fire and drought: Shifts in bark investment across a broad geographical scale for Neotropical savanna trees}, volume={56}, ISSN={["1618-0089"]}, DOI={10.1016/j.baae.2021.06.011}, abstractNote={Savanna tree communities occurring in confluence zones with other biomes likely experience different environmental pressures, resulting in shifts in the selection of individual traits, the combinations of such traits, and species composition. In seasonally dry fire-prone environments, plant survival is presumably associated with adaptive changes in bark properties related to fire protection and water storage. Here, we integrated the multiple functions of the bark to investigate whether different selective pressures could influence patterns of variation in bark structure and allocation across species in a broad geographical range. We measured thickness, density, and water content of the inner and outer bark in branches and the main stem of the 51 most abundant species in three savanna communities differing in climatic aridity, one located at the core region of Cerrado in Central Brazil and the other two at its periphery, in the transition zones with Amazonia and Atlantic forest biomes. We found no difference in outer bark thickness but markedly difference in inner bark thickness between the three plant communities. In the central region, where dry season is long and fire is frequent, branches and main stem showed thicker inner bark. Contrastingly, in the south periphery region, where dry season is short, species showed thinner inner bark in both branches and main stem. Species from the north periphery region, where mean annual precipitation is higher, but fire is frequent and the dry season is also long, showed similar main stem inner bark thickness, but thinner branch inner bark compared to core region species. Our findings support the idea that investing in inner bark thickness and bark moisture may be the most advantageous strategy in plant communities that suffer from high evaporative demand during a long period and are at a high risk of fire.}, journal={BASIC AND APPLIED ECOLOGY}, author={Scalon, Marina Correa and Rossatto, Davi Rodrigo and Oliveras, Imma and Miatto, Raquel Carolina and Gray, Emma Fiona and Chaves Bicalho Domingos, Fabricius Maia and Brum, Fernanda Thiesen and Carlucci, Marcos Bergmann and Hoffmann, William Arthur and Marimon-Junior, Ben Hur and et al.}, year={2021}, month={Nov}, pages={110–121} }
 @article{hoffmann_rodrigues_uncles_rossi_2021, title={Hydraulic segmentation does not protect stems from acute water loss during fire}, volume={41}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/tpab057}, abstractNote={The heat plume associated with fire has been hypothesized to cause sufficient water loss from trees to induce embolism and hydraulic failure. However, it is unclear whether the water transport path remains sufficiently intact during scorching or burning of foliage to sustain high water loss. We measured water uptake by branches of Magnolia grandiflora while exposing them to a range of fire intensities and examined factors influencing continued water uptake after fire. Burning caused a 22-fold mean increase in water uptake, with greatest rates of water loss observed at burn intensities that caused complete consumption of leaves. Such rapid uptake is possible only with steep gradients in water potential, which would likely result in substantial cavitation of xylem and loss of conductivity in intact stems. Water uptake continued after burning was complete and was greatest following burn intensities that killed leaves but did not consume them. This post-fire uptake was mostly driven by rehydration of the remaining tissues, rather than evaporation from the tissues. Our results indicate that the fire plume hypothesis can be expanded to include a wide range of burning conditions experienced by plants. High rates of water loss are sustained during burning, even when leaves are killed or completely consumed.}, number={10}, journal={TREE PHYSIOLOGY}, author={Hoffmann, William A. and Rodrigues, Amanda C. and Uncles, Nicholas and Rossi, Lorenzo}, year={2021}, month={Oct}, pages={1785–1793} }
 @article{flake_abreu_durigan_hoffmann_2021, title={Savannas are not old fields: Functional trajectories of forest expansion in a fire-suppressed Brazilian savanna are driven by habitat generalists}, ISSN={["1365-2435"]}, DOI={10.1111/1365-2435.13818}, abstractNote={Under fire suppression, many tropical savannas transform into forests. Forest expansion entails changes in environmental variables and plant community structure. We hypothesized that forest expansion into savanna results in a shift in community-weighted mean functional traits from stress tolerance to competitiveness, with generalist species having trait values intermediate between those of specialists of savanna and forest habitats. We studied 30 plots distributed over three savanna–forest boundaries undergoing forest expansion in the Brazilian Cerrado, capturing a gradient from open savanna to recently formed forest. We measured functional traits of 116 woody species of savanna specialist, generalist and forest specialist functional groups and quantified changes in species composition and mean traits across the basal area gradient. We identified two main axes of species traits. The first separated forest and generalist species from savanna specialists, with the latter possessing traits associated with resistance to disturbance and stress— such as thick leaves, thick bark, slower height growth and lower shade tolerance. Our second trait axis separated shrubs and understorey trees from pioneer species. Generalist species’ traits did not differ substantially from forest species, nor did they tend to have a typical pioneer strategy. Community-weighted trait means changed linearly with forest development. There was a steady increase in traits associated with competitive dominance rather than stress tolerance and fire resistance, indicating a wholesale shift in the selective environment. Several of these patterns—for example, increasing height and decreasing light requirements—are common in old-field succession. In contrast to old-field succession, we found that SLA increased, leaf thickness decreased and wood density stayed constant. The assembly of forests appears to be shaped by environmental filters that contribute to a functional trajectory distinct from most other studied ecosystems. Our results highlight the importance of the functional composition of the early community and of the early colonizers of the open environment. Differences between savanna and forest specialists reflect the selective effects of the contrasting environments, while the traits of generalists—and their interaction with environmental filters—drive the dynamics of forest expansion. A free Plain Language Summary can be found within the Supporting Information of this article.}, journal={FUNCTIONAL ECOLOGY}, author={Flake, Samuel W. and Abreu, Rodolfo C. R. and Durigan, Giselda and Hoffmann, William A.}, year={2021}, month={May} }
 @article{pilon_durigan_rickenback_pennington_dexter_hoffmann_abreu_lehmann_2021, title={Shade alters savanna grass layer structure and function along a gradient of canopy cover}, volume={32}, ISSN={["1654-1103"]}, DOI={10.1111/jvs.12959}, abstractNote={Aim In savannas, a grass-dominated ground layer is key to ecosystem function via grass–fire feedbacks that maintain open ecosystems. With woody encroachment, tree density increases, thereby decreasing light in the ground layer and potentially altering ecosystem function. We investigated how light availability can filter individual grass species distributions and whether different functional traits are associated with response to a shade gradient in a landscape experiencing woody encroachment. Location Savanna–forest mosaic in the Cerrado domain, southeastern Brazil. Methods Along an encroachment gradient of increasing tree leaf area index (LAI) and shade, we determined how changing light availability alters grass diversity and ground layer structure relative to grass cover and grass functional traits (photosynthetic pathway, underground storage organs, bud protection and traits related to grass shape, size and leaf dimensions). Results Increasing shade led to a decrease in grass cover and grass species richness, and also compositional and functional changes. We found that where tree LAI reached 1, grass cover was reduced by 50% and species richness by 30%. While C4 grass species abundances decreased with increasing shade, the opposite pattern was true for C3 grasses. There were only small differences in light preferences among C4 subtypes, with phosphoenolpyruvate carboxykinase (PCK) species tolerating slightly more shaded conditions. Persistence of some C4 species under more shaded conditions was possible, likely due to an ability to store starch reserves via underground storage organs. Conclusions Woody encroachment changes diversity and structure of the grassy layer that is critical to the functioning of savanna ecosystems, highlighting the dependence of the diverse grass layer on open and sunny conditions. Our results suggest a threshold of tree cover close to LAI ≈ 1 as being critical to cerrado grassy layer conservation.}, number={1}, journal={JOURNAL OF VEGETATION SCIENCE}, author={Pilon, Natashi A. L. and Durigan, Giselda and Rickenback, Jess and Pennington, R. Toby and Dexter, Kyle G. and Hoffmann, William A. and Abreu, Rodolfo C. R. and Lehmann, Caroline E. R.}, year={2021}, month={Jan} }
 @article{pilon_cava_hoffmann_abreu_fidelis_durigan_2021, title={The diversity of post-fire regeneration strategies in the cerrado ground layer}, volume={109}, ISSN={["1365-2745"]}, DOI={10.1111/1365-2745.13456}, abstractNote={Disentangling species strategies that confer resilience to natural disturbances is key to conserving and restoring savanna ecosystems. Fire is a recurrent disturbance in savannas, and savanna vegetation is highly adapted to and often dependent on fire. However, although the woody component of tropical savannas is well studied, we still do not understand how ground-layer plant communities respond to fire, limiting conservation and management actions. We investigated the effects of prescribed fire on community structure and composition, and evaluated which traits are involved in plant community regeneration after fire in the cerrado ground layer. We assessed traits related to species persistence and colonization capacity after fire, including resprouter type, underground structure, fire-induced flowering, regeneration strategy and growth form. We searched for functional groups related to response to fire, to shed light on the main strategies of post-fire recovery among species in the ground layer. Fire changed ground-layer community structure and composition in the short term, leading to greater plant species richness, population densities and increasing bare soil, compared with unburned communities. Eight months after fire, species abundance did not differ from pre-disturbance values for 86% of the species, demonstrating the resilience of this layer to fire. Only one ruderal species was disadvantaged by fire and 13% of the species benefited. Rapid recovery of soil cover by native vegetation in burned areas was driven by species with high capacity to resprout and spread vegetatively. Recovery of the savanna ground-layer community, as a whole, resulted from a combination of different species traits. We summarized these traits into five large groups, encompassing key strategies involved in ground-layer regeneration after fire. Synthesis. Fire dramatically changes the ground layer of savanna vegetation in the short term, but the system is highly resilient, quickly recovering the pre-fire state. Recovery involves different strategies, which we categorized into five functional groups of plant species: grasses, seeders, bloomers, undergrounders and resprouters. Knowledge of these diverse strategies should be used as a tool to assess conservation and restoration status of fire-resilient ecosystems in the cerrado.}, number={1}, journal={JOURNAL OF ECOLOGY}, author={Pilon, Natashi A. L. and Cava, Mario G. B. and Hoffmann, William A. and Abreu, Rodolfo C. R. and Fidelis, Alessandra and Durigan, Giselda}, year={2021}, month={Jan}, pages={154–166} }
 @article{massi_orlando eugenio_franco_hoffmann_2021, title={The effects of tree cover and soil nutrient addition on native herbaceous richness in a neotropical savanna}, volume={53}, ISSN={["1744-7429"]}, DOI={10.1111/btp.12940}, abstractNote={Exotic grasses and high-nutrient availability are common factors that may limit recovery of herbaceous diversity in derived savannas, while tree encroachment is a threat to diversity in old-growth savannas. To understand the impacts of these factors on herbaceous communities, we studied the effect of nutrient addition, and the resulting increase in the exotic grass, Melinis minutiflora, at a savanna-forest boundary in the Brazilian Cerrado. We inventoried richness of reproductive herbs, tree basal area and cover of the exotic grass, Melinis minutiflora, in each plot. Nutrient addition caused a large increase in Melinis and a large decrease in richness of flowering plants. Unexpectedly, structural equation model analysis suggests that the decline in herbaceous richness was a direct result of nutrient addition, rather than an indirect effect caused by the increase in Melinis. Tree density had a strong negative effect on both Melinis cover and herbaceous richness. Our results reveal that high-nutrient availability imposes a barrier to the restoration of a diverse, native herbaceous layer in anthropogenic savannas, while tree encroachment is a threat to diversity in old-growth savannas. Abstract in Portuguese is available with online material. A presença de gramíneas exóticas e alta disponibilidade de nutrientes no solo são fatores comuns que podem limitar a recuperação da diversidade de plantas herbáceas em savanas derivadas, enquanto o adensamento arbóreo é uma ameaça à diversidade dessas espécies em áreas de savanas originais. Para entender os impactos desses fatores nas comunidades herbáceas, estudamos o efeito da adição de nutrientes e o aumento resultante da cobertura da espécie exótica, Melinis minutiflora, em uma área de transição cerrado sensu stricto-mata de galeria no Cerrado brasileiro. Em cada parcela foram inventariadas a riqueza de espécies herbáceas com flores e/ou frutos, a área basal das espécies arbóreas e a cobertura da espécie exótica, Melinis minutiflora. A adição de nutrientes causou um grande aumento em Melinis e uma grande diminuição na riqueza de plantas reprodutivas. Inesperadamente, a análise do modelo de equação estrutural sugere que o declínio na riqueza de herbáceas foi um resultado direto da adição de nutrientes, ao invés de um efeito indireto causado pelo aumento em Melinis. A densidade das árvores teve um forte efeito negativo tanto na cobertura de Melinis quanto na riqueza de herbáceas. Nossos resultados revelam que a alta disponibilidade de nutrientes impõe uma barreira para a restauração de um estrato herbáceo nativo diverso em savanas antropogênicas, enquanto o adensamento arbóreo é uma ameaça à diversidade em áreas de savanas originais. The data that support the findings of this study are available on request from the corresponding author. The Editor-in-Chief has waived the required archiving due to privacy or ethical restrictions. The corresponding author confirms on behalf of all authors that there have been no involvements that might raise the question of bias in the work reported or in the conclusions, implications, or opinions stated. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={3}, journal={BIOTROPICA}, author={Massi, Klecia Gili and Orlando Eugenio, Chesterton Ulysses and Franco, Augusto Cesar and Hoffmann, William A.}, year={2021}, month={May}, pages={888–895} }
 @article{de antonio_hoffmann_rossatto_2021, title={The role of morpho-physiological traits in frost tolerance of neotropical savanna trees}, ISSN={["1432-2285"]}, DOI={10.1007/s00468-021-02150-7}, journal={TREES-STRUCTURE AND FUNCTION}, author={De Antonio, Ariadne C. and Hoffmann, William A. and Rossatto, Davi R.}, year={2021}, month={Jun} }
 @article{hoffmann_sanders_just_wall_hohmann_2020, title={Better lucky than good: How savanna trees escape the fire trap in a variable world}, volume={101}, ISSN={["1939-9170"]}, DOI={10.1002/ecy.2895}, abstractNote={Fire controls tree cover in many savannas by suppressing saplings through repeated topkill and resprouting, causing a demographic bottleneck. Tree cover can increase dramatically if even a small fraction of saplings escape this fire trap, so modeling and management of savanna vegetation should account for occasional individuals that escape the fire trap because they are "better" (i.e., they grow faster than average) or because they are "lucky" (they experience an occasional longer-than-average interval without fire or a below-average fire severity). We quantified variation in growth rates and topkill probability in Quercus laevis (turkey oak) in longleaf pine savanna to estimate the percentage of stems expected to escape the fire trap due to variability in (1) growth rate, (2) fire severity, and (3) fire interval. For trees growing at the mean rate and exposed to the mean fire severity and the mean fire interval, no saplings are expected to become adults under typical fire frequencies. Introducing variability in any of these factors, however, allows some individuals to escape the fire trap. A variable fire interval had the greatest influence, allowing 8% of stems to become adults within a century. In contrast, introducing variation in fire severity and growth rate should allow 2.8% and 0.3% of stems to become adults, respectively. Thus, most trees that escape the fire trap do so because of luck. By chance, they experience long fire-free intervals and/or a low-severity fire when they are not yet large enough to resist an average fire. Fewer stems escape the fire trap by being unusually fast-growing individuals. It is important to quantify these sources of variation and their consequences to improve understanding, prediction, and management of vegetation dynamics of fire-maintained savannas. Here we also present a new approach to quantifying variation in fire severity utilizing a latent-variable model of logistic regression.}, number={1}, journal={ECOLOGY}, author={Hoffmann, William A. and Sanders, R. Wyatt and Just, Michael G. and Wall, Wade A. and Hohmann, Matthew G.}, year={2020}, month={Jan} }
 @article{newberry_power_abreu_durigan_rossatto_hoffmann_2020, title={Flammability thresholds or flammability gradients? Determinants of fire across savanna-forest transitions}, volume={228}, ISSN={["1469-8137"]}, DOI={10.1111/nph.16742}, abstractNote={Vegetation-fire feedbacks are important for determining the distribution of forest and savanna. To understand how vegetation structure controls these feedbacks, we quantified flammability across gradients of tree density from grassland to forest in the Brazilian Cerrado. We experimentally burned 102 plots, for which we measured vegetation structure, fuels, microclimate, ignition success and fire behavior. Tree density had strong negative effects on ignition success, rate of spread, fire-line intensity and flame height. Declining grass biomass was the principal cause of this decline in flammability as tree density increased, but increasing fuel moisture contributed. Although the response of flammability to tree cover often is portrayed as an abrupt, largely invariant threshold, we found the response to be gradual, with considerable variability driven largely by temporal changes in atmospheric humidity. Even when accounting for humidity, flammability at intermediate tree densities cannot be predicted reliably. Fire spread in savanna-forest mosaics is not as deterministic as often assumed, but may appear so where vegetation boundaries are already sharp. Where transitions are diffuse, fire spread is difficult to predict, but should become increasingly predictable over multiple fire cycles, as boundaries are progressively sharpened until flammability appears to respond in a threshold-like manner.}, number={3}, journal={NEW PHYTOLOGIST}, author={Newberry, Brooklynn M. and Power, Collin R. and Abreu, Rodolfo C. R. and Durigan, Giselda and Rossatto, Davi R. and Hoffmann, William A.}, year={2020}, month={Nov}, pages={910–921} }
 @article{durigan_pilon_abreu_hoffmann_martins_fiorillo_antunes_carmignotto_maravalhas_vieira_et al._2020, title={No Net Loss of Species Diversity After Prescribed Fires in the Brazilian Savanna}, volume={3}, ISSN={["2624-893X"]}, DOI={10.3389/ffgc.2020.00013}, abstractNote={Although savannas are fire-adapted ecosystems, prescribing fire for biodiversity conservation remains controversial at least in some regions where savannas occur. Faced with uncertainty, many decision makers and even scientists are still reluctant to prescribe fire for conservation purposes in fire-prone ecosystems, invoking the precautionary principle. Knowledge gaps on the ideal fire regime, such as how and when to burn, and especially the fear of biodiversity losses, are among the main arguments against fire management applied to remnants of native savanna vegetation. To inform this debate, we assessed the impact of prescribed fires on diversity of plants (different growth forms), ants, frogs, lizards, birds, and small mammals, in savannas and grasslands of the Brazilian Cerrado. We assessed the existing species richness, composition, and abundance in areas subjected to long periods of fire suppression and compared to that observed over a short period after prescribed dry-season fires, within each group of plants and animals. Whenever possible, we carried out separate analyses for grassland and savanna. Burning did not significantly reduce species richness of any of the groups analyzed, but had a positive effect on richness of graminoids in grassland. When analyzed at the species level, abundance of most animal groups did not show consistent responses to fire, except for a decrease in some frog populations in grasslands. Forbs, graminoids and subshrubs increased in abundance after fire in grassland areas, though in savanna areas, abundance of forbs and subshrubs tended to decline after fire. Species composition changed little in response to fire as indicated by low levels of dissimilarity between burned and unburned areas. These results confirm the high resilience of Cerrado biota to fire, as expected for savanna ecosystems in general. Besides, we demonstrate here that the risk of biodiversity losses cannot justify the objections to the use of prescribed fire for conservation purposes in the Cerrado.}, journal={FRONTIERS IN FORESTS AND GLOBAL CHANGE}, author={Durigan, Giselda and Pilon, Natashi A. L. and Abreu, Rodolfo C. R. and Hoffmann, William A. and Martins, Marcio and Fiorillo, Bruno F. and Antunes, Alexsander Z. and Carmignotto, Ana Paula and Maravalhas, Jonas B. and Vieira, Jesica and et al.}, year={2020}, month={Feb} }
 @article{gotsch_geiger_franco_goldstein_meinzer_hoffmann_2019, title={Allocation to leaf area and sapwood area affects water relations of co-occurring savanna and forest trees (vol 163, pg 291, 2010)}, volume={189}, ISSN={["1432-1939"]}, DOI={10.1007/s00442-018-04327-3}, abstractNote={The original version of this article unfortunately contained a mistake. The Electronic supplementary material (ESM) was accompanying this article by mistake.}, number={2}, journal={OECOLOGIA}, author={Gotsch, Sybil G. and Geiger, Erika L. and Franco, Augusto C. and Goldstein, Guillermo and Meinzer, Frederick C. and Hoffmann, William A.}, year={2019}, month={Feb}, pages={563–563} }
 @article{veldman_aleman_alvarado_anderson_archibald_bond_boutton_buchmann_buisson_canadell_et al._2019, title={Comment on "The global tree restoration potential"}, volume={366}, ISSN={["1095-9203"]}, DOI={10.1126/science.aay7976}, abstractNote={Bastin et al .’s estimate (Reports, 5 July 2019, p. 76) that tree planting for climate change mitigation could sequester 205 gigatonnes of carbon is approximately five times too large. Their analysis inflated soil organic carbon gains, failed to safeguard against warming from trees at high latitudes and elevations, and considered afforestation of savannas, grasslands, and shrublands to be restoration.}, number={6463}, journal={SCIENCE}, author={Veldman, Joseph W. and Aleman, Julie C. and Alvarado, Swanni T. and Anderson, T. Michael and Archibald, Sally and Bond, William J. and Boutton, Thomas W. and Buchmann, Nina and Buisson, Elise and Canadell, Josep G. and et al.}, year={2019}, month={Oct} }
 @article{hoffmann_flake_abreu_pilon_rossatto_durigan_2019, title={Rare frost events reinforce tropical savanna-forest boundaries}, volume={107}, ISSN={["1365-2745"]}, DOI={10.1111/1365-2745.13047}, number={1}, journal={JOURNAL OF ECOLOGY}, author={Hoffmann, William A. and Flake, Samuel W. and Abreu, Rodolfo C. R. and Pilon, Natashi A. L. and Rossatto, Davi R. and Durigan, Giselda}, year={2019}, month={Jan}, pages={468–477} }
 @article{pilon_hoffmann_abreu_durigan_2018, title={Quantifying the short-term flowering after fire in some plant communities of a cerrado grassland}, volume={11}, ISSN={["1755-1668"]}, DOI={10.1080/17550874.2018.1517396}, abstractNote={ABSTRACTBackground: Fire has been reported to trigger the production of flowers and fruits in many fire-prone ecosystems around the world. However, for tropical savannas, little is known about the effects of fire on flower production at community and species scale, especially for the ground-layer.Aims: We assessed the role of fire as a trigger to short-term flowering in cerrado grassland, compared with unburned vegetation.Methods: We recorded the presence of flowers or fruits in 2,441 individuals from 47 plant species (grasses, forbs and subshrubs), during 6 months after fire, in burned and unburned areas of cerrado grasslands, in south-eastern Brazil.Results: In the burned areas, 63% of individuals sampled flowered, in contrast to 19% in unburned areas, demonstrating a strong and positive effect of fire on plant communities of cerrado grasslands. Fire significantly induced flowering in 79% of the studied species, of which 20 species flowered only after fire (nine grasses, seven subshrubs and four forbs)....}, number={3}, journal={PLANT ECOLOGY & DIVERSITY}, author={Pilon, Natashi A. L. and Hoffmann, William A. and Abreu, Rodolfo C. R. and Durigan, Giselda}, year={2018}, pages={259–266} }
 @article{trugman_medvigy_hoffmann_pellegrini_2018, title={Sensitivity of woody carbon stocks to bark investment strategy in Neotropical savannas and forests}, volume={15}, ISSN={["1726-4189"]}, DOI={10.5194/bg-15-233-2018}, abstractNote={Abstract. Fire frequencies are changing in Neotropical savannas and forests as a result of forest fragmentation and increasing drought. Such changes in fire regime and climate are hypothesized to destabilize tropical carbon storage, but there has been little consideration of the widespread variability in tree fire tolerance strategies. To test how aboveground carbon stocks change with fire frequency and composition of plants with different fire tolerance strategies, we update the Ecosystem Demography model 2 (ED2) with (i) a fire survivorship module based on tree bark thickness (a key fire-tolerance trait across woody plants in savannas and forests), and (ii) plant functional types representative of trees in the region. With these updates, the model is better able to predict how fire frequency affects population demography and aboveground woody carbon. Simulations illustrate that the high survival rate of thick-barked, large trees reduces carbon losses with increasing fire frequency, with high investment in bark being particularly important in reducing losses in the wettest sites. Additionally, in landscapes that frequently burn, bark investment can broaden the range of climate and fire conditions under which savannas occur by reducing the range of conditions leading to either complete tree loss or complete grass loss. These results highlight that tropical vegetation dynamics depend not only on rainfall and changing fire frequencies but also on tree fire survival strategy. Further, our results indicate that fire survival strategy is fundamentally important in regulating tree size demography in ecosystems exposed to fire, which increases the preservation of aboveground carbon stocks and the coexistence of different plant functional groups.}, number={1}, journal={BIOGEOSCIENCES}, author={Trugman, Anna T. and Medvigy, David and Hoffmann, William A. and Pellegrini, Adam F. A.}, year={2018}, month={Jan}, pages={233–243} }
 @article{bagherzadi_sinclair_zwieniecki_secchi_hoffmann_carter_rufty_2017, title={Assessing, water-related plant traits to explain slow-wilting in soybean PI 471938}, volume={31}, ISSN={["1542-7536"]}, DOI={10.1080/15427528.2017.1309609}, abstractNote={ABSTRACTSoybean [Glycine max (L.) Merr.] genotype PI 471938 expresses a slow-wilting phenotype in the field, and the progeny of this genotype have shown to have high yield under water deficit conditions. However, the physiological basis for the slow-wilting trait in PI 471938 remains unclear, and failure to understand the causal mechanism may limit future breeding efforts. This study investigated three primary hypotheses for trait expression that could explain slow-wilting trait in PI 471938: (1) a low osmotic potential in the leaves allowing greater water retention, (2) high elastic modulus of leaves resulting in delayed development of wilting, and (3) high hydraulic conductance allowing rapid water redistribution in the plants. Experiments included three other soybean genotypes as references for the results obtained with PI 471938. Surprisingly, the results for PI 471938 did not prove to be unique as compared to the other three tested genotypes for any of the three hypotheses. These negative results ind...}, number={3}, journal={JOURNAL OF CROP IMPROVEMENT}, author={Bagherzadi, Laleh and Sinclair, Thomas R. and Zwieniecki, Maciej and Secchi, Francesca and Hoffmann, William and Carter, Thomas E. and Rufty, Thomas W.}, year={2017}, pages={400–417} }
 @article{griffith_lehmann_stromberg_parr_pennington_sankaran_ratnam_still_powell_hanan_et al._2017, title={Comment on "The extent of forest in dryland biomes"}, volume={358}, number={6365}, journal={Science}, author={Griffith, D. M. and Lehmann, C. E. R. and Stromberg, C. A. E. and Parr, C. L. and Pennington, R. T. and Sankaran, M. and Ratnam, J. and Still, C. J. and Powell, R. L. and Hanan, N. P. and et al.}, year={2017} }
 @article{pellegrini_anderegg_paine_hoffmann_kartzinel_rabin_sheil_franco_pacala_2017, title={Convergence of bark investment according to fire and climate structures ecosystem vulnerability to future change}, volume={20}, ISSN={["1461-0248"]}, DOI={10.1111/ele.12725}, abstractNote={Fire regimes in savannas and forests are changing over much of the world. Anticipating the impact of these changes requires understanding how plants are adapted to fire. In this study, we test whether fire imposes a broad selective force on a key fire-tolerance trait, bark thickness, across 572 tree species distributed worldwide. We show that investment in thick bark is a pervasive adaptation in frequently burned areas across savannas and forests in both temperate and tropical regions where surface fires occur. Geographic variability in bark thickness is largely explained by annual burned area and precipitation seasonality. Combining environmental and species distribution data allowed us to assess vulnerability to future climate and fire conditions: tropical rainforests are especially vulnerable, whereas seasonal forests and savannas are more robust. The strong link between fire and bark thickness provides an avenue for assessing the vulnerability of tree communities to fire and demands inclusion in global models.}, number={3}, journal={ECOLOGY LETTERS}, author={Pellegrini, Adam F. A. and Anderegg, William R. L. and Paine, C. E. Timothy and Hoffmann, William A. and Kartzinel, Tyler and Rabin, Sam S. and Sheil, Douglas and Franco, Augusto C. and Pacala, Stephen W.}, year={2017}, month={Mar}, pages={307–316} }
 @article{just_hohmann_hoffmann_2017, title={Invasibility of a fire-maintained savanna-wetland gradient by non-native, woody plant species}, volume={405}, ISSN={["1872-7042"]}, DOI={10.1016/j.foreco.2017.09.052}, abstractNote={Abstract Fire-promoting, open-canopy ecosystems are under threat of conversion to a fire-deterring, closed-canopy condition due to woody encroachment. This conversion of vegetation structure has been fostered by introduced woody plant species. We performed a field experiment to quantify growth, survival, and establishment success of six invasive, woody species along a managed longleaf pine savanna–wetland gradient in the Sandhills of North Carolina, USA. We investigated the effects of prescribed fire, fire history, dispersal, and abiotic conditions on the invasibility of sites along the gradient. Across 18 study sites, seeds of the six woody species were sown using three sowing methods that mimicked primary and secondary dispersal; each site contained paired plots located in savanna and savanna-wetland ecotone vegetation communities. We identified sowing treatment, abiotic conditions, seedling size, and prescribed fire as important factors for controlling woody invasion, as they prevented 5 of 6 study species from establishing in the landscape. However, the landscape was not immune to invasion. At the end of the 42-month study period, three species had established in unburned sites. In sites burned after seedling emergence, only one species, Pyrus calleryana, survived and established. We found P. calleryana survival and establishment to be a function of seedling size, soil humic matter content, and sowing treatment. Successful invasion and establishment of woody individuals in open-canopied systems increases the likelihood of fire-deterrence and further woody encroachment, threatening ecosystem integrity.}, journal={FOREST ECOLOGY AND MANAGEMENT}, author={Just, Michael G. and Hohmann, Matthew G. and Hoffmann, William A.}, year={2017}, month={Dec}, pages={229–237} }
 @article{abreu_hoffmann_vasconcelos_pilon_rossatto_durigan_2017, title={The biodiversity cost of carbon sequestration in tropical savanna}, volume={3}, ISSN={["2375-2548"]}, DOI={10.1126/sciadv.1701284}, abstractNote={Forest expansion into Brazilian savanna due to fire suppression causes precipitous species loss.}, number={8}, journal={SCIENCE ADVANCES}, author={Abreu, Rodolfo C. R. and Hoffmann, William A. and Vasconcelos, Heraldo L. and Pilon, Natashi A. and Rossatto, Davi R. and Durigan, Giselda}, year={2017}, month={Aug} }
 @article{giroldo_scariot_hoffmann_2017, title={Trait shifts associated with the subshrub life-history strategy in a tropical savanna}, volume={185}, ISSN={["1432-1939"]}, DOI={10.1007/s00442-017-3930-4}, abstractNote={Over the past 10 million years, tropical savanna environments have selected for small growth forms within woody plant lineages. The result has been the evolution of subshrubs (geoxyles), presumably as an adaptation to frequent fire. To evaluate the traits associated with the shift from tree to subshrub growth forms, we compared seed biomass, germination, survival, resprouting, biomass allocation, and photosynthesis between congeneric trees and subshrubs, and quantified phylogenetic conservatism. Despite large differences in adult morphology between trees and subshrub species, the differences are modest in seedlings, and most of the variation in traits was explained by genus, indicating considerable phylogenic conservatism. Regardless, tree seedlings invested more heavily in aboveground growth, compared to subshrubs, which is consistent with the adult strategy of savanna trees, which depend on a large resistant-fire stem. Subshrub seedlings also invest in greater non-structural carbohydrate reserves, likely as an adaptation to the high fire frequencies typical of tropical savannas. The modest differences as seedlings suggest that selective pressures during early development may not have contributed substantially to the evolution of the subshrub growth form and that the distinct allocation and life history must arise later in life. This is consistent with the interpretation that the subshrub growth form arose as a life-history strategy in which maturity is reached at a small stem size, allowing them to reproduce despite repeated fire-induced topkill. The convergent evolution of subshrubs within multiple tree lineages reaffirms the importance of fire in the origin and diversification of the flora of mesic savannas.}, number={2}, journal={OECOLOGIA}, author={Giroldo, A. B. and Scariot, A. and Hoffmann, W. A.}, year={2017}, month={Oct}, pages={281–291} }
 @article{just_schafer_hohmann_hoffmann_2017, title={Wood decay and the persistence of resprouting species in pyrophilic ecosystems}, volume={31}, ISSN={["1432-2285"]}, DOI={10.1007/s00468-016-1477-3}, number={1}, journal={TREES-STRUCTURE AND FUNCTION}, author={Just, Michael G. and Schafer, Jennifer L. and Hohmann, Matthew G. and Hoffmann, William A.}, year={2017}, month={Feb}, pages={237–245} }
 @article{geng_liu_ji_hoffmann_grunden_xiang_2016, title={Enhancing Heat Tolerance of the Little Dogwood Cornus canadensis L. f. with Introduction of a Superoxide Reductase Gene from the Hyperthermophilic Archaeon Pyrococcus furiosus}, volume={7}, ISSN={1664-462X}, url={http://dx.doi.org/10.3389/fpls.2016.00026}, DOI={10.3389/fpls.2016.00026}, abstractNote={Production of reactive oxygen species (ROS) can be accelerated under various biotic and abiotic stresses causing lipid peroxidation, protein degradation, enzyme inactivation, and DNA damage. Superoxide reductase (SOR) is a novel antioxidant enzyme from Pyrococcus furiosus and is employed by this anaerobic hyperthermophilic archaeon for efficient detoxification of ROS. In this study, SOR was introduced into a flowering plant Cornus canadensis to enhance its heat tolerance and reduce heat induced damage. A fusion construct of the SOR gene and Green Fluorescent Protein gene (GFP) was introduced into C. canadensis using Agrobacterium-mediated transformation. Heat tolerance of the GFP-SOR expressing transgenic plants was investigated by observing morphological symptoms of heat injury and by examining changes in photosynthesis, malondialdehyde (MDA), and proline levels in the plants. Our results indicate that the expression of the P. furiosus SOR gene in the transgenic plants alleviated lipid peroxidation of cell membranes and photoinhibition of PS II, and decreased the accumulation of proline at 40°C. After a series of exposures to increasing temperatures, the SOR transgenic plants remained healthy and green whereas most of the non-transgenic plants dried up and were unable to recover. While it had previously been reported that expression of SOR in Arabidopsis enhanced heat tolerance, this is the first report of the successful demonstration of improved heat tolerance in a non-model plant resulting from the introduction of P. furiosus SOR. The study demonstrates the potential of SOR for crop improvement and that inherent limitations of plant heat tolerance can be ameliorated with P. furiosus SOR.}, journal={Frontiers in Plant Science}, publisher={Frontiers Media SA}, author={Geng, Xing-Min and Liu, Xiang and Ji, Mikyoung and Hoffmann, William A. and Grunden, Amy and Xiang, Qiu-Yun J.}, year={2016}, month={Jan} }
 @article{pellegrini_franco_hoffmann_2016, title={Shifts in functional traits elevate risk of fire-driven tree dieback in tropical savanna and forest biomes}, volume={22}, ISSN={["1365-2486"]}, DOI={10.1111/gcb.13110}, abstractNote={Numerous predictions indicate rising CO2 will accelerate the expansion of forests into savannas. Although encroaching forests can sequester carbon over the short term, increased fires and drought-fire interactions could offset carbon gains, which may be amplified by the shift toward forest plant communities more susceptible to fire-driven dieback. We quantify how bark thickness determines the ability of individual tree species to tolerate fire and subsequently determine the fire sensitivity of ecosystem carbon across 180 plots in savannas and forests throughout the 2.2-million km(2) Cerrado region in Brazil. We find that not accounting for variation in bark thickness across tree species underestimated carbon losses in forests by ~50%, totaling 0.22 PgC across the Cerrado region. The lower bark thicknesses of plant species in forests decreased fire tolerance to such an extent that a third of carbon gains during forest encroachment may be at risk of dieback if burned. These results illustrate that consideration of trait-based differences in fire tolerance is critical for determining the climate-carbon-fire feedback in tropical savanna and forest biomes.}, number={3}, journal={GLOBAL CHANGE BIOLOGY}, author={Pellegrini, Adam F. A. and Franco, Augusto C. and Hoffmann, William A.}, year={2016}, month={Mar}, pages={1235–1243} }
 @article{marchin_broadhead_bostic_dunn_hoffmann_2016, title={Stomatal acclimation to vapour pressure deficit doubles transpiration of small tree seedlings with warming}, volume={39}, ISSN={0140-7791}, url={http://dx.doi.org/10.1111/pce.12790}, DOI={10.1111/pce.12790}, abstractNote={Future climate change is expected to increase temperature (T) and atmospheric vapour pressure deficit (VPD) in many regions, but the effect of persistent warming on plant stomatal behaviour is highly uncertain. We investigated the effect of experimental warming of 1.9-5.1 °C and increased VPD of 0.5-1.3 kPa on transpiration and stomatal conductance (gs ) of tree seedlings in the temperate forest understory (Duke Forest, North Carolina, USA). We observed peaked responses of transpiration to VPD in all seedlings, and the optimum VPD for transpiration (Dopt ) shifted proportionally with increasing chamber VPD. Warming increased mean water use of Carya by 140% and Quercus by 150%, but had no significant effect on water use of Acer. Increased water use of ring-porous species was attributed to (1) higher air T and (2) stomatal acclimation to VPD resulting in higher gs and more sensitive stomata, and thereby less efficient water use. Stomatal acclimation maintained homeostasis of leaf T and carbon gain despite increased VPD, revealing that short-term stomatal responses to VPD may not be representative of long-term exposure. Acclimation responses differ from expectations of decreasing gs with increasing VPD and may necessitate revision of current models based on this assumption.}, number={10}, journal={Plant, Cell & Environment}, publisher={Wiley}, author={Marchin, Renée M. and Broadhead, Alice A. and Bostic, Laura E. and Dunn, Robert R. and Hoffmann, William A.}, year={2016}, month={Aug}, pages={2221–2234} }
 @article{just_hohmann_hoffmann_2016, title={Where fire stops: vegetation structure and microclimate influence fire spread along an ecotonal gradient}, volume={217}, ISSN={["1573-5052"]}, DOI={10.1007/s11258-015-0545-x}, number={6}, journal={PLANT ECOLOGY}, author={Just, Michael G. and Hohmann, Matthew G. and Hoffmann, William A.}, year={2016}, month={Jun}, pages={631–644} }
 @article{carlson_dole_matthysse_hoffmann_kornegay_2015, title={Bacteria species and solution pH effect postharvest quality of cut Zinnia elegans}, volume={194}, ISSN={["1879-1018"]}, DOI={10.1016/j.scienta.2015.07.044}, abstractNote={Bacterial growth in vase solutions can lead to stem vasculature blockage causing petal and leaf wilt, bent neck, or similar symptoms related to water stress that reduce vase life. In these studies we isolated, identified, and evaluated the effects of several bacteria species on the vase life of cut Zinnia elegans L. ‘Benary’s Giant Wine’. Nine bacterial species were isolated during postharvest testing of cut zinnia stems: Pseudomonas fulva, Serratia ficaria, Rhizobium radiobacter, Chryseobacterium sp., Pantoea ananatis, Bacillus pumilus, Chryseobacterium daejeonense, Brevundimonas sp., and Pseudomonas marginalis and pure cultures of each species were added to the vase solution of cut zinnia stems. Escherichia coli K12, a lab adapted strain, was also included. Cut flowers inoculated with P. fulva and E. coli K12 had significantly greater vase lives of 9.5 and 9.4 d, respectively, compared to P. marginalis, P. ananatis, R. radiobacter, or the nutrient broth control (7.0, 6.9, 6.8, or 7.3 d, respectively). The vase lives of the other bacteria treatments were not statistically different from the deionized (DI) water control (8.6 d). There were no significant differences in water uptake or vase water bacteria concentrations at termination among all treatments. In further studies, sterilized and non-sterilized stems of Zinnia were used to investigate the effects of solution pH and the addition of P. marginalis and E. coli K12 on number of days to drought stress (DTDS), stem hydraulic conductivity, and bacteria concentrations inside and outside the stem. The non-sterilized stems in control solution with E. coli K12 and non-sterilized stems in preservative solution with no bacteria had the most DTDS of 8.0 d. The sterilized stems in the control solution (deionized water) with E. coli K12 and sterilized stems in basic solution with no bacteria had the least DTDS of 5.5 d and 5.8 d, respectively. The concentrations of bacteria inside and outside the stems were lowest for stems in the preservative solutions. Of the stems that were sterilized, partial percent loss of conductivity (PPLC) was significantly lower in the acidic solutions (64%) compared to the preservative (87%) and control (83%). This research shows that for Zinnia the bacteria species that has a primary effect on vase life, not necessarily the concentration of bacteria in the vase solution.}, journal={SCIENTIA HORTICULTURAE}, author={Carlson, Alicain S. and Dole, John M. and Matthysse, Ann G. and Hoffmann, William A. and Kornegay, Julia L.}, year={2015}, month={Oct}, pages={71–78} }
 @article{schafer_breslow_hohmann_hoffmann_2015, title={RELATIVE BARK THICKNESS IS CORRELATED WITH TREE SPECIES DISTRIBUTIONS ALONG A FIRE FREQUENCY GRADIENT}, volume={11}, ISSN={["1933-9747"]}, DOI={10.4996/fireecology.1101074}, abstractNote={The probability of stem survival after fire is strongly influenced by energy allocation to bark because bark thickness affects heat transfer during fire. Greater relative investment in inner bark versus outer bark should also enhance survival because of greater moisture content of inner bark. We measured stem diameter, bark thickness, and habitat preference of five species typical of long-leaf pine savannas, and six species characteristic of adjacent wetlands (pocosins), and calculated relative bark thickness, the inner bark proportion, radial growth, and bark accumulation of each species. We hypothesized that savanna species have thicker bark and greater relative investment in inner bark than pocosin species, because fires occur more frequently in savannas than pocosins. As hypothesized, savanna species have relatively thicker bark than pocosin species. Relative bark thickness and the rate of bark accumulation were correlated with the mean location of a species along the pocosin-to-savanna gradient. However, the inner bark proportion did not differ between savanna and pocosin species. Our results indicate that relative bark thickness is likely the primary bark trait affecting fire-induced topkill and influencing the distribution of species along the pocosin-to-savanna gradient.}, number={1}, journal={FIRE ECOLOGY}, author={Schafer, Jennifer L. and Breslow, Bradley P. and Hohmann, Matthew G. and Hoffmann, William A.}, year={2015}, pages={74–87} }
 @article{marchin_salk_hoffmann_dunn_2015, title={Temperature alone does not explain phenological variation of diverse temperate plants under experimental warming}, volume={21}, ISSN={["1365-2486"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84937524423&partnerID=MN8TOARS}, DOI={10.1111/gcb.12919}, abstractNote={Anthropogenic climate change has altered temperate forest phenology, but how these trends will play out in the future is controversial. We measured the effect of experimental warming of 0.6–5.0 °C on the phenology of a diverse suite of 11 plant species in the deciduous forest understory (Duke Forest, North Carolina, USA) in a relatively warm year (2011) and a colder year (2013). Our primary goal was to dissect how temperature affects timing of spring budburst, flowering, and autumn leaf coloring for functional groups with different growth habits, phenological niches, and xylem anatomy. Warming advanced budburst of six deciduous woody species by 5–15 days and delayed leaf coloring by 18–21 days, resulting in an extension of the growing season by as much as 20–29 days. Spring temperature accumulation was strongly correlated with budburst date, but temperature alone cannot explain the diverse budburst responses observed among plant functional types. Ring-porous trees showed a consistent temperature response pattern across years, suggesting these species are sensitive to photoperiod. Conversely, diffuse-porous species responded differently between years, suggesting winter chilling may be more important in regulating budburst. Budburst of the ring-porous Quercus alba responded nonlinearly to warming, suggesting evolutionary constraints may limit changes in phenology, and therefore productivity, in the future. Warming caused a divergence in flowering times among species in the forest community, resulting in a longer flowering season by 10-16 days. Temperature was a good predictor of flowering for only four of the seven species studied here. Observations of interannual temperature variability overpredicted flowering responses in spring-blooming species, relative to our warming experiment, and did not consistently predict even the direction of flowering shifts. Experiments that push temperatures beyond historic variation are indispensable for improving predictions of future changes in phenology.}, number={8}, journal={GLOBAL CHANGE BIOLOGY}, author={Marchin, Renee M. and Salk, Carl F. and Hoffmann, William A. and Dunn, Robert R.}, year={2015}, month={Aug}, pages={3138–3151} }
 @article{marchin_dunn_hoffmann_2014, title={Are winter-active species vulnerable to climate warming? A case study with the wintergreen terrestrial orchid, Tipularia discolor}, volume={176}, ISSN={["1432-1939"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84921938451&partnerID=MN8TOARS}, DOI={10.1007/s00442-014-3074-8}, number={4}, journal={OECOLOGIA}, author={Marchin, Renee M. and Dunn, Robert R. and Hoffmann, William A.}, year={2014}, month={Dec}, pages={1161–1172} }
 @article{pellegrini_hoffmann_franco_2014, title={Carbon accumulation and nitrogen pool recovery during transitions from savanna to forest in central Brazil}, volume={95}, ISSN={["1939-9170"]}, DOI={10.1890/13-0290.1}, abstractNote={The expansion of tropical forest into savanna may potentially be a large carbon sink, but little is known about the patterns of carbon sequestration during transitional forest formation. Moreover, it is unclear how nutrient limitation, due to extended exposure to fire-driven nutrient losses, may constrain carbon accumulation. Here, we sampled plots that spanned a woody biomass gradient from savanna to transitional forest in response to differential fire protection in central Brazil. These plots were used to investigate how the process of transitional forest formation affects the size and distribution of carbon (C) and nitrogen (N) pools. This was paired with a detailed analysis of the nitrogen cycle to explore possible connections between carbon accumulation and nitrogen limitation. An analysis of carbon pools in the vegetation, upper soil, and litter shows that the transition from savanna to transitional forest can result in a fourfold increase in total carbon (from 43 to 179 Mg C/ha) with a doubling of carbon stocks in the litter and soil layers. Total nitrogen in the litter and soil layers increased with forest development in both the bulk (+68%) and plant-available (+150%) pools, with the most pronounced changes occurring in the upper layers. However, the analyses of nitrate concentrations, nitrate:ammonium ratios, plant stoichiometry of carbon and nitrogen, and soil and foliar nitrogen isotope ratios suggest that a conservative nitrogen cycle persists throughout forest development, indicating that nitrogen remains in low supply relative to demand. Furthermore, the lack of variation in underlying soil type (>20 cm depth) suggests that the biogeochemical trends across the gradient are driven by vegetation. Our results provide evidence for high carbon sequestration potential with forest encroachment on savanna, but nitrogen limitation may play a large and persistent role in governing carbon sequestration in savannas or other equally fire-disturbed tropical landscapes. In turn, the link between forest development and nitrogen pool recovery creates a framework for evaluating potential positive feedbacks on savanna-forest boundaries.}, number={2}, journal={ECOLOGY}, author={Pellegrini, Adam F. A. and Hoffmann, William A. and Franco, Augusto C.}, year={2014}, month={Feb}, pages={342–352} }
 @article{wall_douglas_hoffmann_wentworth_gray_xiang_knaus_hohmann_g._2014, title={Evidence of population bottleneck in Astragalus michauxii (Fabaceae), a narrow endemic of the southeastern United States}, volume={15}, ISSN={1566-0621, 1572-9737}, url={http://link.springer.com/10.1007/s10592-013-0527-2}, DOI={10.1007/s10592-013-0527-2}, number={1}, journal={Conservation Genetics}, publisher={Springer Science and Business Media LLC}, author={Wall, W. A. and Douglas, N. A. and Hoffmann, W. A. and Wentworth, T. R. and Gray, J. B. and Xiang, Q. Y. J. and Knaus, B. K. and Hohmann and G., M.}, year={2014}, month={Feb}, pages={153–164} }
 @article{lehmann_anderson_sankaran_higgins_archibald_hoffmann_hanan_williams_fensham_felfili_et al._2014, title={Savanna vegetation-fire-climate relationships differ among continents}, volume={343}, number={6170}, journal={Science}, author={Lehmann, C. E. R. and Anderson, T. M. and Sankaran, M. and Higgins, S. I. and Archibald, S. and Hoffmann, W. A. and Hanan, N. P. and Williams, R. J. and Fensham, R. J. and Felfili, J. and et al.}, year={2014}, pages={548–552} }
 @article{schafer_breslow_hollingsworth_hohmann_hoffmann_2014, title={Size-dependent enhancement of water relations during post-fire resprouting}, volume={34}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/tpu015}, abstractNote={In resprouting species, fire-induced topkill causes a reduction in height and leaf area without a comparable reduction in the size of the root system, which should lead to an increase in the efficiency of water transport after fire. However, large plants undergo a greater relative reduction in size, compared with small plants, so we hypothesized that this enhancement in hydraulic efficiency would be greatest among large growth forms. In the ecotone between long-leaf pine (Pinus palustris Mill.) savannas and wetlands, we measured stomatal conductance (gs), mid-day leaf water potential (Ψleaf), leaf-specific whole-plant hydraulic conductance (KL.p), leaf area and height of 10 species covering a range of growth forms in burned and unburned sites. As predicted, KL.p was higher in post-fire resprouts than in unburned plants, and the post-fire increase in KL.p was positively related to plant size. Specifically, large-statured species tended to undergo the greatest relative reductions in leaf area and height, and correspondingly experienced the greatest increases in KL.p. The post-fire increase in KL.p was smaller than expected, however, due to a decrease in absolute root hydraulic conductance (i.e., not scaled to leaf area). The higher KL.p in burned sites was manifested as an increase in gs rather than an increase in Ψleaf. Post-fire increases in gs should promote high rates of photosynthesis for recovery of carbohydrate reserves and aboveground biomass, which is particularly important for large-statured species that require more time to recover their pre-fire size.}, number={4}, journal={TREE PHYSIOLOGY}, author={Schafer, Jennifer L. and Breslow, Bradley P. and Hollingsworth, Stephanie N. and Hohmann, Matthew G. and Hoffmann, William A.}, year={2014}, month={Apr}, pages={404–414} }
 @article{parr_lehmann_bond_hoffmann_andersen_2014, title={Tropical grassy biomes: misunderstood, neglected, and under threat}, volume={29}, ISSN={["1872-8383"]}, DOI={10.1016/j.tree.2014.02.004}, abstractNote={•Tropical grassy biomes are extensive and critical to human livelihoods. •The definition of these grassy systems is inconsistent and misleading. •We discuss novel threats linked to problems with biome definition. •The assumption that ‘more trees are better’ does not hold for tropical grassy biomes. Tropical grassy biomes (TGBs) are globally extensive, provide critical ecosystem services, and influence the earth–atmosphere system. Yet, globally applied biome definitions ignore vegetation characteristics that are critical to their functioning and evolutionary history. Hence, TGB identification is inconsistent and misinterprets the ecological processes governing vegetation structure, with cascading negative consequences for biodiversity. Here, we discuss threats linked to the definition of TGB, the Clean Development Mechanism (CDM) and Reducing Emissions from Deforestation and Forest Degradation schemes (REDD+), and enhanced atmospheric CO2, which may facilitate future state shifts. TGB degradation is insidious and less visible than in forested biomes. With human reliance on TGBs and their propensity for woody change, ecology and evolutionary history are fundamental to not only the identification of TGBs, but also their management for future persistence. Tropical grassy biomes (TGBs) are globally extensive, provide critical ecosystem services, and influence the earth–atmosphere system. Yet, globally applied biome definitions ignore vegetation characteristics that are critical to their functioning and evolutionary history. Hence, TGB identification is inconsistent and misinterprets the ecological processes governing vegetation structure, with cascading negative consequences for biodiversity. Here, we discuss threats linked to the definition of TGB, the Clean Development Mechanism (CDM) and Reducing Emissions from Deforestation and Forest Degradation schemes (REDD+), and enhanced atmospheric CO2, which may facilitate future state shifts. TGB degradation is insidious and less visible than in forested biomes. With human reliance on TGBs and their propensity for woody change, ecology and evolutionary history are fundamental to not only the identification of TGBs, but also their management for future persistence. the type of carbon assimilation performed by most plants. This is the most efficient form of photosynthesis under moderate to cool temperatures, high CO2 concentrations, and high water availability. a form of photosynthesis that is evolutionarily derived from C3 photosynthesis, but which includes an additional mechanism for actively transporting CO2 into specialized cells where photosynthesis occurs. This makes C4 plants particularly tolerant of high temperatures, low water availability, and/or low CO2 concentration. C4 photosynthesis is most common among grasses, including maize, millet, and sorghum. the quantity of carbon contained in a ‘pool’, meaning a reservoir that has the capacity to accumulate or release carbon. It refers to both live and dead material and is usually separated in to the amount of carbon stored above ground (e.g., trees, grasses, dead wood, and litter) and that stored below ground (e.g., in soils, roots, and peat). tropical moist savanna in Brazil, accounting for >20% of the land area of the country; very varied in form from dense grassland to almost closed canopied savanna; also includes wetland areas. a carbon-trading system established by the Kyoto Protocol designed to allow a country with an emission-reduction commitment to implement projects in developing countries. Such projects can earn saleable, certified emission reduction credits, each equivalent to 1 t of CO2; these can count towards meeting Kyoto targets. Under CDM, the only eligible forestry projects are afforestation and reforestation projects. a herbaceous flowering plant, other than a graminoid (grasses, sedges, and rushes). plant with underground storage organs (e.g., bulbs, tubers, or corms), which provide reserves of carbohydrates, nutrients, and water. microscopic silica bodies that form in the cells of many kinds of plant. They can be used to identify plant remains in archaeological and palaeoecological work.}, number={4}, journal={TRENDS IN ECOLOGY & EVOLUTION}, author={Parr, Catherine L. and Lehmann, Caroline E. R. and Bond, William J. and Hoffmann, William A. and Andersen, Alan N.}, year={2014}, month={Apr}, pages={205–213} }
 @article{silva_hoffmann_rossatto_haridasan_franco_horwath_2013, title={Can savannas become forests? A coupled analysis of nutrient stocks and fire thresholds in central Brazil}, volume={373}, ISSN={["1573-5036"]}, DOI={10.1007/s11104-013-1822-x}, number={1-2}, journal={PLANT AND SOIL}, author={Silva, Lucas C. R. and Hoffmann, William A. and Rossatto, Davi R. and Haridasan, Mundayatan and Franco, Augusto C. and Horwath, William R.}, year={2013}, month={Dec}, pages={829–842} }
 @article{schafer_breslow_just_hohmann_hollingsworth_swatling-holcomb_hoffmann_2013, title={Current and Historical Variation in Wiregrass (Aristida stricta) Abundance and Distribution Is Not Detectable from Soil delta C-13 Measurements in Longleaf Pine (Pinus palustris) Savannas}, volume={78}, ISSN={["1938-4386"]}, DOI={10.2179/12-021}, abstractNote={Plant species distributions and transitions between vegetation types are determined by numerous factors, including disturbances such as fire. Documentation of past changes in the distribution and structure of fire-dependent ecosystems is necessary to assess the success of land management in maintaining historic vegetation types. In our study system—longleaf pine (Pinus palustris)-wiregrass (Aristida stricta) savannas and embedded wetlands (i.e., pocosins)—wiregrass is dependent on frequent burning. We used soil carbon (C) isotopes to test for past changes in the abundance of wiregrass and for shifts in the ecotone between savanna and pocosin in four sites at Fort Bragg, North Carolina. Wiregrass has a C4 photosynthetic pathway and therefore produces organic matter enriched in 13C compared to other dominant species in the community that have a C3 photosynthetic pathway. At each of the four sites, we measured profiles of soil δ13C to a depth of 1 m at four locations along the vegetation gradient from upland savannas to lowland pocosins. Surface soil δ13C, which reflects C inputs from current vegetation, did not differ along the gradient despite a decrease in wiregrass cover from savanna, where it is abundant, to pocosin, where it is absent. Enrichment of soil δ13C with depth was indistinguishable from effects of decomposition, indicating that past variation in the abundance and distribution of wiregrass was not detectable in our study sites. Our results suggest that wiregrass currently does not produce, and historically has not produced, enough biomass to influence soil δ13C values along the savanna-pocosin gradient.}, number={1}, journal={CASTANEA}, author={Schafer, Jennifer L. and Breslow, Bradley P. and Just, Michael G. and Hohmann, Matthew G. and Hollingsworth, Stephanie N. and Swatling-Holcomb, Samantha L. and Hoffmann, William A.}, year={2013}, month={Mar}, pages={28–36} }
 @article{rossatto_hoffmann_ramos silva_haridasan_sternberg_franco_2013, title={Seasonal variation in leaf traits between congeneric savanna and forest trees in Central Brazil: implications for forest expansion into savanna}, volume={27}, ISSN={["1432-2285"]}, DOI={10.1007/s00468-013-0864-2}, number={4}, journal={TREES-STRUCTURE AND FUNCTION}, author={Rossatto, Davi Rodrigo and Hoffmann, William Arthur and Ramos Silva, Lucas de Carvalho and Haridasan, Mundayatan and Sternberg, Leonel S. L. and Franco, Augusto Cesar}, year={2013}, month={Aug}, pages={1139–1150} }
 @article{grady_hoffmann_2012, title={Caught in a fire trap: Recurring fire creates stable size equilibria in woody resprouters}, volume={93}, ISSN={["1939-9170"]}, DOI={10.1890/12-0354.1}, abstractNote={Globally, fire maintains many mesic habitats in an open canopy state by killing woody plants while reducing the size of those able to resprout. Where fire is frequent, tree saplings are often suppressed by a “fire trap” of repeated topkill (death of aerial biomoass) and resprouting, preventing them from reaching adult size. The ability to tolerate repeated topkill is an essential life-history trait that allows a sapling to persist until it experiences a long fire-free interval, during which it can escape the fire trap. We hypothesized that persistence in the fire trap results from a curvilinear relationship between pre-burn size and resprout size, which causes a plant to approach an equilibrial size in which post-fire biomass recovery is equal to fire-induced biomass loss. We also predicted that the equilibrial stem size is positively related to resource availability. To test these hypotheses, we collected data on pre-burn and resprout size of five woody plant species at wetland ecotones in longleaf pine savanna subjected to frequent burning. As expected, all species exhibited similar curvilinear relationships between pre-burn size and resprout size. The calculated equilibrial sizes were strong predictors of mean plant size across species and growing conditions, supporting the persistence equilibrium model. An alternative approach using matrix models yielded similar results. Resprouting was less vigorous in dry sites than at wet sites, resulting in smaller equilibrial stem sizes in drier sites; extrapolating these results provides an explanation for the absence of these species in xeric uplands. This new framework offers a straightforward approach to guide data collection for experimental, comparative, and modeling studies of plant persistence and community dynamics in frequently burned habitats.}, number={9}, journal={ECOLOGY}, author={Grady, John M. and Hoffmann, William A.}, year={2012}, month={Sep}, pages={2052–2060} }
 @article{wall_hoffmann_wentworth_gray_hohmann_2012, title={Demographic effects of fire on two endemic plant species in the longleaf pine-wiregrass ecosystem}, volume={213}, ISSN={["1385-0237"]}, DOI={10.1007/s11258-012-0068-7}, number={7}, journal={PLANT ECOLOGY}, author={Wall, Wade A. and Hoffmann, William A. and Wentworth, Thomas R. and Gray, Janet B. and Hohmann, Matthew G.}, year={2012}, month={Jul}, pages={1093–1104} }
 @misc{hoffmann_geiger_gotsch_rossatto_silva_lau_haridasan_franco_2012, title={Ecological thresholds at the savanna-forest boundary: how plant traits, resources and fire govern the distribution of tropical biomes}, volume={15}, ISSN={["1461-0248"]}, DOI={10.1111/j.1461-0248.2012.01789.x}, abstractNote={Fire shapes the distribution of savanna and forest through complex interactions involving climate, resources and species traits. Based on data from central Brazil, we propose that these interactions are governed by two critical thresholds. The fire-resistance threshold is reached when individual trees have accumulated sufficient bark to avoid stem death, whereas the fire-suppression threshold is reached when an ecosystem has sufficient canopy cover to suppress fire by excluding grasses. Surpassing either threshold is dependent upon long fire-free intervals, which are rare in mesic savanna. On high-resource sites, the thresholds are reached quickly, increasing the probability that savanna switches to forest, whereas low-resource sites are likely to remain as savanna even if fire is infrequent. Species traits influence both thresholds; saplings of savanna trees accumulate bark thickness more quickly than forest trees, and are more likely to become fire resistant during fire-free intervals. Forest trees accumulate leaf area more rapidly than savanna trees, thereby accelerating the transition to forest. Thus, multiple factors interact with fire to determine the distribution of savanna and forest by influencing the time needed to reach these thresholds. Future work should decipher multiple environmental controls over the rates of tree growth and canopy closure in savanna.}, number={7}, journal={ECOLOGY LETTERS}, author={Hoffmann, William A. and Geiger, Erika L. and Gotsch, Sybil G. and Rossatto, Davi R. and Silva, Lucas C. R. and Lau, On Lee and Haridasan, M. and Franco, Augusto C.}, year={2012}, month={Jul}, pages={759–768} }
 @article{hoffmann_jaconis_mckinley_geiger_gotsch_franco_2012, title={Fuels or microclimate? Understanding the drivers of fire feedbacks at savanna-forest boundaries}, volume={37}, ISSN={["1442-9985"]}, DOI={10.1111/j.1442-9993.2011.02324.x}, abstractNote={The higher flammability of tropical savanna, compared with forest, plays a critical role in mediating vegetation-environment feedbacks, alternate stable states, and ultimately, the distribution of these two biomes. Multiple factors contribute to this difference in flammability, including microclimate, fuel amount and fuel type. To understand this transition in flammability, we studied fuel characteristics and microclimate across eight savanna–forest boundaries in south-central Brazil. At each boundary, the environment was monitored for one week with automated measurements of near-surface wind speed, air temperature, relative humidity and presence of dew. Manual measurements were performed to quantify fuel amounts and fuel moisture. These data were used to parameterize the fire behaviour model BehavePlus5 in order to simulate fire behaviour over the savanna–forest boundary. There were strong gradients across the boundary in all variables with the exception of total fuel load. During the day, savannas had higher wind speed and air temperature, and lower relative humidity and fuel moisture than forests. Although fuel loads were similar in savanna and forest, savanna was characterized by lower fuel bulk density, largely because of the presence of grasses. Based on these measurements, the fire behaviour model predicted savanna fires to be faster, more intense, and with greater flame lengths, relative to forest. A sensitivity analysis indicated that the primary cause of these differences was the low fuel bulk density characteristic of grassy fuels, with lesser contributions from wind speed, fuel moisture and total fuel load. These results indicate that the dominance of grassy fuels is the primary cause of the high flammability of savanna.}, number={6}, journal={AUSTRAL ECOLOGY}, author={Hoffmann, William A. and Jaconis, Susany. and Mckinley, Kristen L. and Geiger, Erika L. and Gotsch, Sybil G. and Franco, Augusto C.}, year={2012}, month={Sep}, pages={634–643} }
 @article{lehmann_archibald_hoffmann_bond_2011, title={Deciphering the distribution of the savanna biome}, volume={191}, ISSN={["1469-8137"]}, DOI={10.1111/j.1469-8137.2011.03689.x}, abstractNote={Summary
•We aimed to identify the limits of savanna across Africa, Australia and South America. We based our investigation on the rich history of hypotheses previously examined: that the limits of savanna are variously determined by rainfall, rainfall seasonality, soil fertility and disturbance.
•We categorized vegetation on all continents as ‘savanna’ (open habitats with a C4 grass layer) or ‘not-savanna’ (closed habitats with no C4 grass layer) and used a combination of statistical approaches to examine how the presence of savanna varied as a function of five environmental correlates.
•The presence of savanna is constrained by effective rainfall and rainfall seasonality. Soil fertility is regionally important, although the direction of its effect changes relative to rainfall. We identified three continental divergences in the limits of savanna that could not be explained by environment.
•Climate and soils do not have a deterministic effect on the distribution of savanna. Over the range of savanna, some proportion of the land is always ‘not-savanna’. We reconciled previous contradictory views of savanna limits by developing a new conceptual framework for understanding these limits by categorizing environmental factors into whether they had a positive or negative effect on woody growth and the frequency of disturbance.}, number={1}, journal={NEW PHYTOLOGIST}, author={Lehmann, Caroline E. R. and Archibald, Sally A. and Hoffmann, William A. and Bond, William J.}, year={2011}, pages={197–209} }
 @article{geiger_gotsch_damasco_haridasan_franco_hoffmann_2011, title={Distinct roles of savanna and forest tree species in regeneration under fire suppression in a Brazilian savanna}, volume={22}, ISSN={["1654-1103"]}, DOI={10.1111/j.1654-1103.2011.01252.x}, abstractNote={Questions: Has fire suppression relaxed barriers to the exchange of species between savanna and forest? Do all species or a subset of species participate in this exchange? Would current vegetation structure persist if fire suppression were to cease? Location: A gallery forest edge in the Cerrado region of central Brazil that burned only once in the past 35 years. Methods: Density of tree seedlings, saplings and adults, leaf area index (LAI), tree basal area and diameter were surveyed in 12, 10m � 70m transects centred on and perpendicular to the forest‐savanna boundary. Community composition was assessed using non-metric multi-dimensional scaling (NMDS). Results: Basal area and LAI declined substantially from forest to savanna, with an associated shift in species composition. Savanna tree species were nearly absent in the forest, but accounted for the majority of stems in the savanna. In contrast, forest species comprised 14% of adults and more than one-third of juveniles in the savanna. Despite the high diversity of trees (85 species) in the forest, five species play a particularly large role in this initial phase of forest expansion. Reintroduction of fire, however, would result in widespread topkill of juveniles and the majority of adult forest trees, thereby interrupting the succession towards forest. Conclusions: After 35 years during which the site burned only once, the savanna still remains dominated by savanna species. Nevertheless, the dominance of forest juveniles in border and savanna tree communities suggests that with a continued policy of fire suppression, the forest will continue to expand.}, number={2}, journal={JOURNAL OF VEGETATION SCIENCE}, author={Geiger, Erika L. and Gotsch, Sybil G. and Damasco, Gabriel and Haridasan, M. and Franco, Augusto C. and Hoffmann, William A.}, year={2011}, month={Apr}, pages={312–321} }
 @article{hoffmann_marchin_abit_lau_2011, title={Hydraulic failure and tree dieback are associated with high wood density in a temperate forest under extreme drought}, volume={17}, ISSN={["1365-2486"]}, DOI={10.1111/j.1365-2486.2011.02401.x}, abstractNote={Catastrophic hydraulic failure will likely be an important mechanism contributing to large-scale tree dieback caused by increased frequency and intensity of droughts under global climate change. To compare the susceptibility of 22 temperate deciduous tree and shrub species to hydraulic failure during a record drought in the southeastern USA, we quantified leaf desiccation, native embolism, wood density, stomatal conductance and predawn and midday leaf water potential at four sites with varying drought intensities. At the two driest sites, there was widespread leaf wilting and desiccation, and most species exhibited predawn leaf water potentials of ≤3 MPa and >60% loss of xylem conductivity in branches. Although species with high wood density were more resistant to cavitation, they had higher levels of native embolism and greater canopy dieback than species with low wood density. This unexpected result can be explained by the failure of species with dense wood to avert a decline in water potential to dangerous levels during the drought. Leaf water potential was negatively correlated with wood density, and the relationship was strongest under conditions of severe water deficit. Species with low wood density avoided catastrophic embolism by relying on an avoidance strategy that involves partial drought deciduousness, higher sensitivity of stomata to leaf water potential and perhaps greater rooting depth. These species therefore maintained water potential at levels that ensured a greater margin of safety against embolism. These differences among species may mediate rapid shifts in species composition of temperate forests if droughts intensify due to climate change.}, number={8}, journal={GLOBAL CHANGE BIOLOGY}, author={Hoffmann, William A. and Marchin, Renee M. and Abit, Pamela and Lau, On Lee}, year={2011}, month={Aug}, pages={2731–2742} }
 @article{wall_wentworth_shelingoski_stucky_leblond_hoffmann_2011, title={Lost and Found: Remnants of the Big Savannah and Their Relationship to Wet Savannas in North Carolina}, volume={76}, ISSN={["1938-4386"]}, DOI={10.2179/10-046.1}, abstractNote={Abstract Conversion to agriculture and plantations, development, and fire suppression have reduced the extent of savannas in the southeastern United States, and there is a need to catalog and classify the remaining savannas for both restoration and resource management purposes. The Big Savannah was a wet savanna in North Carolina that was destroyed in the 1950s, and subsequent vegetation classifications have generally not accommodated well the unique natural plant community of the Big Savannah. Vegetation reminiscent of that described for the Big Savannah was discovered north of the original site and designated as Wells Savannah. To evaluate the uniqueness of the savanna vegetation at Wells Savannah, we compiled a data set from permanent quadrats with information on vegetation and environmental variables from other Outer Coastal Plain savannas to compare with similar data from the natural community at Wells Savannah. We also inventoried an additional 26 quadrats on a tract adjacent to Wells Savannah that ...}, number={4}, journal={CASTANEA}, author={Wall, W. A. and Wentworth, T. R. and Shelingoski, S. and Stucky, J. M. and LeBlond, R. J. and Hoffmann, W. A.}, year={2011}, month={Dec}, pages={348–363} }
 @article{douglas_wall_xiang_hoffmann_wentworth_gray_hohmann_2011, title={Recent vicariance and the origin of the rare, edaphically specialized Sandhills lily, Lilium pyrophilum (Liliaceae): evidence from phylogenetic and coalescent analyses}, volume={20}, ISSN={["0962-1083"]}, DOI={10.1111/j.1365-294x.2011.05151.x}, abstractNote={Establishing the phylogenetic and demographic history of rare plants improves our understanding of mechanisms that have led to their origin and can lead to valuable insights that inform conservation decisions. The Atlantic coastal plain of eastern North America harbours many rare and endemic species, yet their evolution is poorly understood. We investigate the rare Sandhills lily (Lilium pyrophilum), which is endemic to seepage slopes in a restricted area of the Atlantic coastal plain of eastern North America. Using phylogenetic evidence from chloroplast, nuclear internal transcribed spacer and two low-copy nuclear genes, we establish a close relationship between L. pyrophilum and the widespread Turk's cap lily, L. superbum. Isolation-with-migration and coalescent simulation analyses suggest that (i) the divergence between these two species falls in the late Pleistocene or Holocene and almost certainly post-dates the establishment of the edaphic conditions to which L. pyrophilum is presently restricted, (ii) vicariance is responsible for the present range disjunction between the two species, and that subsequent gene flow has been asymmetrical and (iii) L. pyrophilum harbours substantial genetic diversity in spite of its present rarity. This system provides an example of the role of edaphic specialization and climate change in promoting diversification in the Atlantic coastal plain.}, number={14}, journal={MOLECULAR ECOLOGY}, author={Douglas, Norman A. and Wall, Wade A. and Xiang, Qiu-Yun and Hoffmann, William A. and Wentworth, Thomas R. and Gray, Janet B. and Hohmann, Matthew G.}, year={2011}, month={Jul}, pages={2901–2915} }
 @article{ratnam_bond_fensham_hoffmann_archibald_lehmann_anderson_higgins_sankaran_2011, title={When is a 'forest' a savanna, and why does it matter?}, volume={20}, ISSN={["1466-8238"]}, DOI={10.1111/j.1466-8238.2010.00634.x}, abstractNote={Savannas are defined based on vegetation structure, the central concept being a discontinuous tree cover in a continuous grass understorey. However, at the high-rainfall end of the tropical savanna biome, where heavily wooded mesic savannas begin to structurally resemble forests, or where tropical forests are degraded such that they open out to structurally resemble savannas, vegetation structure alone may be inadequate to distinguish mesic savanna from forest. Additional knowledge of the functional differences between these ecosystems which contrast sharply in their evolutionary and ecological history is required. Specifically, we suggest that tropical mesic savannas are predominantly mixed tree–C4 grass systems defined by fire tolerance and shade intolerance of their species, while forests, from which C4 grasses are largely absent, have species that are mostly fire intolerant and shade tolerant. Using this framework, we identify a suite of morphological, physiological and life-history traits that are likely to differ between tropical mesic savanna and forest species. We suggest that these traits can be used to distinguish between these ecosystems and thereby aid their appropriate management and conservation. We also suggest that many areas in South Asia classified as tropical dry forests, but characterized by fire-resistant tree species in a C4 grass-dominated understorey, would be better classified as mesic savannas requiring fire and light to maintain the unique mix of species that characterize them.}, number={5}, journal={GLOBAL ECOLOGY AND BIOGEOGRAPHY}, author={Ratnam, Jayashree and Bond, William J. and Fensham, Rod J. and Hoffmann, William A. and Archibald, Sally and Lehmann, Caroline E. R. and Anderson, Michael T. and Higgins, Steven I. and Sankaran, Mahesh}, year={2011}, month={Sep}, pages={653–660} }
 @article{gotsch_geiger_franco_goldstein_meinzer_hoffmann_2010, title={Allocation to leaf area and sapwood area affects water relations of co-occurring savanna and forest trees}, volume={163}, ISSN={["1432-1939"]}, DOI={10.1007/s00442-009-1543-2}, number={2}, journal={OECOLOGIA}, author={Gotsch, Sybil G. and Geiger, Erika L. and Franco, Augusto C. and Goldstein, Guillermo and Meinzer, Frederick C. and Hoffmann, William A.}, year={2010}, month={Jun}, pages={291–301} }
 @article{marchin_zeng_hoffmann_2010, title={Drought-deciduous behavior reduces nutrient losses from temperate deciduous trees under severe drought}, volume={163}, ISSN={["1432-1939"]}, DOI={10.1007/s00442-010-1614-4}, number={4}, journal={OECOLOGIA}, author={Marchin, Renee and Zeng, Hainian and Hoffmann, William}, year={2010}, month={Aug}, pages={845–854} }
 @article{wall_hilton_wentworth_gray_hohmann_hoffmann_2010, title={Effects of light and temperature on germination of Pyxidanthera brevifolia Wells (Diapensiaceae)}, volume={137}, ISSN={["1940-0616"]}, DOI={10.3159/10-ra-023.1}, abstractNote={Pyxidanthera brevifolia is an evergreen semi-woody cushion plant endemic to the Sandhills of North and South Carolina, with the majority of populations occurring on Fort Bragg Military Reservation in North Carolina. Currently the species is listed as Endangered in North Carolina and is designated as a Species at Risk (SAR) by the US Department of Defense. Previous studies have suggested that seeds may not be viable because they failed to germinate under controlled conditions. Our objectives in this study were to attempt germination of Pyxidanthera brevifolia seeds, determine the best temperature conditions for germination, and understand more about germination requirements to aid in future restoration efforts. Using seeds that had been stored at room temperature for six months, we performed a germination experiment at the NCSU Phytotron with six treatments, all combinations of three temperature regimes (low (18 °C day / 14 °C night), medium (22/18 °C), and high (26/22 °C)) and two light conditions (light and dark). We monitored the experiment for 13 weeks, recording the number of seeds germinating per dish and the number of days to germination for seeds in each treatment. We found that Pxyidanthera brevifolia produces germinable seeds and that there are significant effects of light and temperature on germination. Highest germination occurred under low temperature and high light conditions (78%); the combination of high temperature and no light produced the lowest germination (6%). Seeds exposed to light germinated significantly earlier at the coolest temperature, compared to medium and high temperatures. These results indicate that it is possible to germinate seeds of this rare plant and suggest that germination of Pyxidanthera brevifolia likely occurs in late fall and is dependent on adequate light availability.}, number={4}, journal={JOURNAL OF THE TORREY BOTANICAL SOCIETY}, author={Wall, Wade A. and Hilton, Jacob L. and Wentworth, Thomas R. and Gray, Janet B. and Hohmann, Matthew G. and Hoffmann, William A.}, year={2010}, pages={348–354} }
 @article{scholz_bucci_hoffmann_meinzer_goldstein_2010, title={Hydraulic lift in a Neotropical savanna: Experimental manipulation and model simulations}, volume={150}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2010.02.001}, abstractNote={The objective of this study was to assess the magnitude of hydraulic lift in Brazilian savannas (Cerrado) and to test the hypothesis that hydraulic lift by herbaceous plants contributes substantially to slowing the decline of water potential and water storage in the upper soil layers during the dry season. To this effect, field observations of soil water content and water potentials, an experimental manipulation, and model simulations, were used. Savannas of central Brazil exhibit consistent changes in tree density along shallow topographic gradients, from open savannas with relatively few trees in the lower portions of the topographic gradients to woodlands with a relatively high density of trees in the upper portions of the gradient. Herbaceous plant abundance follows the opposite trend. The diel recovery of soil water storage was higher in sites with more abundant herbaceous vegetation. Experimental removal of the above ground portion of herbaceous plants in a site with low tree density, during the dry season, substantially enhanced diel recovery of water potentials in the upper soil layers, consistent with the release of hydraulically lifted water from their shallow roots. In a site with high tree density, the release of hydraulically lifted water by woody plants contributed only 2% to the partial daily recovery of soil water storage, whereas the herbaceous layer contributed the remaining 98%. Non saturated water flow in the same savanna type contributed 8% to the partial daily recovery of soil water potential at the beginning of the dry season, decreasing to near 0% after 20 days of drought. During a 70-day rainless period the soil water potential dropped to −2.0 MPa near the soil surface. The simulation model predicted that without hydraulic lift, water potential in the upper soil layers in relatively dense savannas would have dropped to −3.8 MPa. The maximum contribution of hydraulic lift to the upper 100 cm of soil was 0.7 mm day−1 near the middle of the dry season. During the peak of the dry season, hydraulic lift can replace 23% of the ecosystem evapotranspiration in a site with high tree density and consequently greatly influences the water economy and other ecosystem processes in the Cerrado.}, number={4}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Scholz, Fabian G. and Bucci, Sandra J. and Hoffmann, William A. and Meinzer, Frederick C. and Goldstein, Guillermo}, year={2010}, month={Apr}, pages={629–639} }
 @article{silva_haridasan_sternberg_franco_hoffmann_2010, title={Not all forests are expanding over central Brazilian savannas}, volume={333}, ISSN={["1573-5036"]}, DOI={10.1007/s11104-010-0358-6}, number={1-2}, journal={PLANT AND SOIL}, author={Silva, Lucas C. R. and Haridasan, Mundayatan and Sternberg, Leonel S. L. and Franco, Augusto C. and Hoffmann, William A.}, year={2010}, month={Aug}, pages={431–442} }
 @article{marchin_bhandari_wall_hohmann_gray_hoffmann_2009, title={Are rare species less shade tolerant than common species in fire-prone environments? A test with seven Amorpha (Fabaceae) species}, volume={205}, ISSN={["1573-5052"]}, DOI={10.1007/s11258-009-9614-3}, number={2}, journal={PLANT ECOLOGY}, author={Marchin, Renee M. and Bhandari, Rohit K. and Wall, Wade A. and Hohmann, Matthew G. and Gray, Janet B. and Hoffmann, William A.}, year={2009}, month={Dec}, pages={249–260} }
 @article{rossatto_hoffmann_franco_2009, title={Differences in growth patterns between co-occurring forest and savanna trees affect the forest-savanna boundary}, volume={23}, ISSN={["1365-2435"]}, DOI={10.1111/j.1365-2435.2009.01568.x}, abstractNote={1 Patterns of growth, activity and renewal of stems and branches are primary determinants of ecosystem function and strongly influence net primary productivity, water and energy balance. Here we compare patterns of leaf phenology, stem radial growth and branch growth of co-occurring savanna and forest trees in the Cerrado region of central Brazil to gain insight into the influence of these parameters in forest–savanna boundary dynamics. We hypothesized that forest species would have higher radial growth rates but later leaf flush than savanna species. 2 We studied 12 congeneric species pairs, each containing one savanna species and one forest species. All individuals were growing in savanna conditions under full sun. We measured specific leaf area (SLA), light-saturated photosynthesis and monthly increments in stem circumference, branch length, leaf flush and leaf fall. 3 Relative to savanna species, forest species had 68% higher diameter growth rates, 38% higher SLA, and displayed a greater crown area for a given basal area. Across species, radial growth was positively correlated with SLA (r2 = 0·31), but not with CO2 assimilation. 4 Peak leaf production of savanna species was in the late dry season, 1 month earlier than for forest species, which suggests a strategy to avoid nutrient losses during leaf expansion due to herbivory or leaching. However, savanna and forest species did not differ in annual branch growth, number of leaves produced per branch, or in timing of leaf fall. 5 Radial growth was tightly coupled to monthly rainfall in forest species whereas the growth of savanna species ceased before the end of the wet season. The cessation of above-ground growth at a time of active photosynthesis may reflect a shift in allocation to roots and reserves. 6 These results contribute to recent studies showing that savanna and forest species represent different functional types and that despite the limiting resources in savanna environments, forest trees that invade the savanna tend to present higher growth rates and larger and denser crowns, which enhance shading and could promote changes in equilibrium of forest–savanna boundaries.}, number={4}, journal={FUNCTIONAL ECOLOGY}, author={Rossatto, Davi Rodrigo and Hoffmann, William Arthur and Franco, Augusto Cesar}, year={2009}, month={Aug}, pages={689–698} }
 @article{giambelluca_scholz_bucci_meinzer_goldstein_hoffmann_franco_buchert_2009, title={Evapotranspiration and energy balance of Brazilian savannas with contrasting tree density}, volume={149}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2009.03.006}, abstractNote={Tropical savannas including those of central Brazil (Cerrado) serve as an important regulator of energy and mass exchange with the atmosphere. However, the effects of interactions between grasses and deeply rooted trees and shrubs on energy and water fluxes of savannas are not well understood. In this study, eddy-covariance measurements were used to observe and compare the energy balance and evapotranspiration at two adjacent Cerrado sites differing in woody plant density. Latent energy flux (LE) and evapotranspiration (ET) for Cerrado Denso (8-10-m trees with a cover density of approximately 50% and an understory of grass and shrubs) were generally similar to or greater than for Campo Cerrado (widely scattered 3-4-m trees with a cover density of about 5% and an understory of grasses, shrubs, and sedges), with the greatest difference between the sites occurring during the dry season. Mean annual ET was 823 and 689 mm yr � 1 , and LE averaged 63.9 � 11.7 and 53.5 � 14.3 W m � 2 at Cerrado Denso and Campo Cerrado, respectively. At both sites, ET reached a minimum at near the end of the dry season, indicating that reduced water availability constrained dry season ET at both sites. The Bowen ratio at both sites increased as soil moisture decreased, but with a stronger dependency at the Campo Cerrado site, presumably due to the dominance of shallow-rooted plants and the larger contribution of soil evaporation there. Energy partitioning, as indicated by the Bowen ratio, was also strongly influenced by variations in leaf area index (LAI). The strong similarity in the Bowen ratio-LAI relationship for the two sites suggests that LAI can be used to explain much of the observed temporal and spatial ET}, number={8}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Giambelluca, Thomas W. and Scholz, Fabian G. and Bucci, Sandra J. and Meinzer, Frederick C. and Goldstein, Guillermo and Hoffmann, William A. and Franco, Augusto C. and Buchert, Martin P.}, year={2009}, month={Aug}, pages={1365–1376} }
 @article{zhang_meinzer_hao_scholz_bucci_takahashi_villalobos-vega_giraldo_cao_hoffmann_et al._2009, title={Size-dependent mortality in a Neotropical savanna tree: the role of height-related adjustments in hydraulic architecture and carbon allocation}, volume={32}, ISSN={["1365-3040"]}, DOI={10.1111/j.1365-3040.2009.02012.x}, abstractNote={Size-related changes in hydraulic architecture, carbon allocation and gas exchange of Sclerolobium paniculatum (Leguminosae), a dominant tree species in Neotropical savannas of central Brazil (Cerrado), were investigated to assess their potential role in the dieback of tall individuals. Trees greater than approximately 6-m-tall exhibited more branch damage, larger numbers of dead individuals, higher wood density, greater leaf mass per area, lower leaf area to sapwood area ratio (LA/SA), lower stomatal conductance and lower net CO(2) assimilation than small trees. Stem-specific hydraulic conductivity decreased, while leaf-specific hydraulic conductivity remained nearly constant, with increasing tree size because of lower LA/SA in larger trees. Leaves were substantially more vulnerable to embolism than stems. Large trees had lower maximum leaf hydraulic conductance (K(leaf)) than small trees and all tree sizes exhibited lower K(leaf) at midday than at dawn. These size-related adjustments in hydraulic architecture and carbon allocation apparently incurred a large physiological cost: large trees received a lower return in carbon gain from their investment in stem and leaf biomass compared with small trees. Additionally, large trees may experience more severe water deficits in dry years due to lower capacity for buffering the effects of hydraulic path-length and soil water deficits.}, number={10}, journal={PLANT CELL AND ENVIRONMENT}, author={Zhang, Yong-Jiang and Meinzer, Frederick C. and Hao, Guang-You and Scholz, Fabian G. and Bucci, Sandra J. and Takahashi, Frederico S. C. and Villalobos-Vega, Randol and Giraldo, Juan P. and Cao, Kun-Fang and Hoffmann, William A. and et al.}, year={2009}, month={Oct}, pages={1456–1466} }
 @article{rossatto_hoffmann_franco_2009, title={Stomatal traits of cerrado and gallery forest congeneric pairs growing in a transitional region in Central Brazil}, volume={23}, ISSN={["1677-941X"]}, DOI={10.1590/S0102-33062009000200021}, abstractNote={Em áreas protegidas do fogo, espécies arbóreas predominantemente florestais conseguem se estabelecer no cerrado e crescer lado a lado com espécies do mesmo gênero que são características destas formações savânicas. Devido às condições ambientais diferenciadas encontradas nas formações de cerrado e de mata, estas espécies congenéricas podem se comportar como grupos funcionais distintos. Neste trabalho foi realizado um estudo comparativo da anatomia dos estômatos e da condutância estomática e taxas de transpiração foliar em 10 pares de espécies congenéricas do cerrado e de mata de galeria e das relações entre as características estomáticas selecionadas e a condutância estomática, já que a morfologia dos estômatos e sua densidade afetam a área para difusão dos gases e sua trajetória através dos poros estomáticos. Cada par foi de uma família diferente. Para a maioria das espécies, a área do poro estomático foi o fator de maior influencia no processo de trocas gasosas, pela sua correlação com a condutância estomática, enquanto a densidade estomática mostrou uma correlação negativa significativa tanto com o comprimento da célula-guarda quanto com a área do poro estomático. As espécies do cerrado apresentaram valores significativamente maiores do comprimento da célula-guarda e do poro estomático. No entanto, para a maioria dos outros parâmetros estomáticos examinados, a maior parte da variação pode ser atribuída a diferenças entre os gêneros, sendo que a variação entre as espécies dos dois ambientes parece ser um produto da historia evolutiva de cada grupo e não reflete uma especialização ao ambiente de cerrado ou de mata de galeria.}, number={2}, journal={ACTA BOTANICA BRASILICA}, author={Rossatto, Davi Rodrigo and Hoffmann, William Arthur and Franco, Augusto Cesar}, year={2009}, pages={499–508} }
 @article{hoffmann_adasme_haridasan_carvalho_geiger_pereira_gotsch_franco_2009, title={Tree topkill, not mortality, governs the dynamics of savanna-forest boundaries under frequent fire in central Brazil}, volume={90}, ISSN={["1939-9170"]}, DOI={10.1890/08-0741.1}, abstractNote={Tropical savanna and forest are recognized to represent alternate stable states, primarily determined by feedbacks with fire. Vegetation–fire dynamics in each of these vegetation types are largely determined by the influence of the vegetation on fire behavior, as well as the effects of fire behavior on tree mortality, topkill (defined here as complete death of the aerial biomass, regardless of whether the plant recovers by resprouting), and rate of growth of resprouts. We studied the effect of fire on three savanna–forest boundaries in central Brazil. Fire intensity was greater in savanna than forest, as inferred by a twofold greater height of stem charring. Despite lower fire intensity, forest tree species exhibited higher rates of topkill, which was best explained by their thinner bark, relative to savanna species. Following topkill, there was no tendency for sprouts of savanna trees to grow faster than those of forest species, contrary to expectations, nor was whole-plant mortality higher in forest than in savanna. This contrasts with observations of high rates of postburn mortality in many other tropical forests. The low tree mortality in these transitional forests suggests that the dynamic of these natural savanna–forest boundaries is fundamentally different from that of forest boundaries originating from deforestation in the humid tropics. The forests studied here appear to be much more resilient to occasional incursion of fire from the savanna, despite being unable to invade frequently burned savanna. The thin bark of forest species makes them particularly susceptible to the “fire trap,” whereby repeated topkill of small trees prevents recruitment into adult size classes. Rapid growth will be particularly important for forest species to escape the fire trap, so we predict that, where fire is frequent, forests should be restricted to high-resource sites. Here, Mg2+ and Ca2+ concentrations had particularly strong effects on postburn growth rates, suggesting that these elements may most strongly limit the distribution of forest in these fire-prone savannas.}, number={5}, journal={ECOLOGY}, author={Hoffmann, William A. and Adasme, Ryan and Haridasan, M. and Carvalho, Marina T. and Geiger, Erika L. and Pereira, Mireia A. B. and Gotsch, Sybil G. and Franco, Augusto C.}, year={2009}, month={May}, pages={1326–1337} }
 @article{bucci_scholz_goldstein_hoffmann_meinzer_franco_giambelluca_miralles-wilhelm_2008, title={Controls on stand transpiration and soil water utilization along a tree density gradient in a Neotropical savanna}, volume={148}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2007.11.013}, abstractNote={Environmental controls of stand-level tree transpiration (E) and seasonal patterns of soil water utilization were studied in five central Brazilian savanna (Cerrado) sites differing in tree density. Tree density of Cerrado vegetation in the study area consistently changes along topographic gradients from � 1000 trees ha � 1 in open savannas (campo sujo) at the lower end of the topographic gradient to >3000 trees ha � 1 in woodlands (cerradao) at the upper end of the gradient. Tree canopy resistance (rC) increased linearly with increasing daily mean air saturation deficit (D) at all sites, but cerradao and cerrado denso sites with higher tree density and higher tree leaf area index (LAI) had lower rC values at all values of D compared to physiognomies with lower tree density, suggesting that rC was less sensitive to changes in D in physiognomies with high tree density and LAI. During the peak of the dry season, mean soil water potential at 0.20 m depth was most negative in the sites with the lowest tree basal area and increased linearly with basal area across sites. In contrast, soil water storage in the 0.10-2.50 m layer decreased exponentially with increasing basal area, consistent with trees in higher density sites utilizing a larger proportion of available soil water at depth during the dry season. Maximum tree transpiration was highest in the cerradao and cerrado denso (� 0.81 mm day � 1 ). Despite higher evaporative demand during the dry season, E was similar between the dry and wet seasons within each study site, which was associated with lower LAIand canopy conductance (gC)during the dryseason compared to the wet season. Leaf area index was a good predictor of E and gC. For both dry and wet season data combined, E increased asymptotically with increasing LAI across all physiog- nomic types, allowing LAI to be used as a predictor of spatial variation of E. The lack of seasonality in E across the Cerrado physiognomies studied could not be explained by}, number={6-7}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Bucci, Sandra J. and Scholz, Fabian G. and Goldstein, Guillermo and Hoffmann, William A. and Meinzer, Frederick C. and Franco, Augusto C. and Giambelluca, Thomas and Miralles-Wilhelm, Fernando}, year={2008}, month={Jun}, pages={839–849} }
 @article{silva_sternberg_haridasan_hoffmann_miralles-wilhelm_franco_2008, title={Expansion of gallery forests into central Brazilian savannas}, volume={14}, ISSN={["1365-2486"]}, DOI={10.1111/j.1365-2486.2008.01637.x}, abstractNote={Upland tropical forests have expanded and contracted in response to past climates, but it is not clear whether similar dynamics were exhibited by gallery (riparian) forests within savanna biomes. Because such forests generally have access to ample water, their extent may be buffered against changing climates. We tested the long-term stability of gallery forest boundaries by characterizing the border between gallery forests and savannas and tracing the presence of gallery forest through isotopic analysis of organic carbon in the soil profile. We measured leaf area index, grass vs. shrub or tree coverage, the organic carbon, phosphorus, nitrogen and calcium concentrations in soils and the carbon isotope ratios of soil organic matter in two transitions spanning gallery forests and savanna in a Cerrado ecosystem. Gallery forests without grasses typically show a greater leaf area index in contrast to savannas, which show dense grass coverage. Soils of gallery forests have significantly greater concentrations of organic carbon, phosphorus, nitrogen and calcium than those of savannas. Soil organic carbon of savannas is significantly more enriched in 13 C compared with that of gallery forests. This difference in enrichment is in part caused by the presence of C 4 grasses in savanna ecosystem and its absence in gallery forests. Using the 13 C abundance as a signature for savanna and gallery forest ecosystems in 1 m soil cores, we show that the borders of gallery forests have expanded into the savanna and that this process initiated at least 3000-4000 BP based on 14 C analysis. Gallery forests, however, may be still expanding as we found more recent transitions according to 14 C activity measurements. We discuss the possible mechanisms of gallery forest expansion and the means by which nutrients required for the expansion of gallery forest might accumulate.}, number={9}, journal={GLOBAL CHANGE BIOLOGY}, author={Silva, Lucas C. R. and Sternberg, Leonel and Haridasan, Mundayatan and Hoffmann, William A. and Miralles-Wilhelm, Fernando and Franco, Augusto C.}, year={2008}, month={Sep}, pages={2108–2118} }
 @article{hao_hoffmann_scholz_bucci_meinzer_franco_cao_goldstein_2008, title={Stem and leaf hydraulics of congeneric tree species from adjacent tropical savanna and forest ecosystems}, volume={155}, ISSN={["1432-1939"]}, DOI={10.1007/s00442-007-0918-5}, abstractNote={Leaf and stem functional traits related to plant water relations were studied for six congeneric species pairs, each composed of one tree species typical of savanna habitats and another typical of adjacent forest habitats, to determine whether there were intrinsic differences in plant hydraulics between these two functional types. Only individuals growing in savanna habitats were studied. Most stem traits, including wood density, the xylem water potential at 50% loss of hydraulic conductivity, sapwood area specific conductivity, and leaf area specific conductivity did not differ significantly between savanna and forest species. However, maximum leaf hydraulic conductance (K (leaf)) and leaf capacitance tended to be higher in savanna species. Predawn leaf water potential and leaf mass per area were also higher in savanna species in all congeneric pairs. Hydraulic vulnerability curves of stems and leaves indicated that leaves were more vulnerable to drought-induced cavitation than terminal branches regardless of genus. The midday K (leaf) values estimated from leaf vulnerability curves were very low implying that daily embolism repair may occur in leaves. An electric circuit analog model predicted that, compared to forest species, savanna species took longer for their leaf water potentials to drop from predawn values to values corresponding to 50% loss of K (leaf) or to the turgor loss points, suggesting that savanna species were more buffered from changes in leaf water potential. The results of this study suggest that the relative success of savanna over forest species in savanna is related in part to their ability to cope with drought, which is determined more by leaf than by stem hydraulic traits. Variation among genera accounted for a large proportion of the total variance in most traits, which indicates that, despite different selective pressures in savanna and forest habitats, phylogeny has a stronger effect than habitat in determining most hydraulic traits.}, number={3}, journal={OECOLOGIA}, author={Hao, Guang-You and Hoffmann, William A. and Scholz, Fabian G. and Bucci, Sandra J. and Meinzer, Frederick C. and Franco, Augusto C. and Cao, Kun-Fang and Goldstein, Guillermo}, year={2008}, month={Mar}, pages={405–415} }
 @article{hoffmann_haridasan_2008, title={The invasive grass, Melinis minutiflora, inhibits tree regeneration in a Neotropical savanna}, volume={33}, ISSN={["1442-9985"]}, DOI={10.1111/j.1442-9993.2007.01787.x}, abstractNote={Exotic grasses are becoming increasingly abundant in Neotropical savannas, with Melinis minutiflora Beauv. being particularly invasive.To better understand the consequences for the native flora, we performed a field study to test the effect of this species on the establishment, survival and growth of seedlings of seven tree species native to the savannas and forests of the Cerrado region of Brazil. Seeds of the tree species were sown in 40 study plots, of which 20 were sites dominated by M. minutiflora, and 20 were dominated by native grasses. The exotic grass had no discernable effect on initial seedling emergence, as defined by the number of seedlings present at the end of the first growing season.Subsequent seedling survival in plots dominated by M. minutiflora was less than half that of plots dominated by native species. Consequently, at the end of the third growing season, invaded plots had only 44% as many seedlings as plots with native grasses. Above-ground grass biomass of invaded plots was more than twice that of uninvaded plots, while seedling survival was negatively correlated with grass biomass, suggesting that competition for light may explain the low seedling survival where M. minutiflora is dominant. Soils of invaded plots had higher mean Ca, Mg and Zn, but these variables did not account for the higher grass biomass or the lower seedling survival in invaded plots. The results indicate that this exotic grass is having substantial effects on the dynamics of the tree community, with likely consequences for ecosystem structure and function.}, number={1}, journal={AUSTRAL ECOLOGY}, author={Hoffmann, William A. and Haridasan, M.}, year={2008}, month={Feb}, pages={29–36} }
 @article{goldstein_meinzer_bucci_scholz_franco_hoffmann_2008, title={Water economy of Neotropical savanna trees: six paradigms revisited}, volume={28}, ISSN={["1758-4469"]}, DOI={10.1093/treephys/28.3.395}, abstractNote={Biologists have long been puzzled by the striking morphological and anatomical characteristics of Neotropical savanna trees which have large scleromorphic leaves, allocate more than half of their total biomass to belowground structures and produce new leaves during the peak of the dry season. Based on results of ongoing interdisciplinary projects in the savannas of central Brazil (cerrado), we reassessed the validity of six paradigms to account for the water economy of savanna vegetation. (1) All savanna woody species are similar in their ability to take up water from deep soil layers where its availability is relatively constant throughout the year. (2) There is no substantial competition between grasses and trees for water resources during the dry season because grasses exclusively explore upper soil layers, whereas trees access water in deeper soil layers. (3) Tree species have access to abundant groundwater, their stomatal control is weak and they tend to transpire freely. (4) Savanna trees experience increased water deficits during the dry season despite their access to deep soil water. (5) Stomatal conductance of savanna species is low at night to prevent nocturnal transpiration, particularly during the dry season. (6) Savanna tree species can be classified into functional groups according to leaf phenology. We evaluated each paradigm and found differences in the patterns of water uptake between deciduous and evergreen tree species, as well as among evergreen tree species, that have implications for regulation of tree water balance. The absence of resource interactions between herbaceous and woody plants is refuted by our observation that herbaceous plants use water from deep soil layers that is released by deep-rooted trees into the upper soil layer. We obtained evidence of strong stomatal control of transpiration and show that most species exhibit homeostasis in maximum water deficit, with midday water potentials being almost identical in the wet and dry seasons. Although stomatal control is strong during the day, nocturnal transpiration is high during the dry season. Our comparative studies showed that the grouping of species into functional categories is somewhat arbitrary and that ranking species along continuous functional axes better represents the ecological complexity of adaptations of cerrado woody species to their seasonal environment.}, number={3}, journal={TREE PHYSIOLOGY}, author={Goldstein, Guillermo and Meinzer, Frederick C. and Bucci, Sandra J. and Scholz, Fabian G. and Franco, Augusto C. and Hoffmann, William A.}, year={2008}, month={Mar}, pages={395–404} }
 @article{lahoreau_barot_gignoux_hoffmann_setterfield_williams_2006, title={Positive effect of seed size on seedling survival in fire-prone savannas of Australia, Brazil and West Africa}, volume={22}, ISSN={["1469-7831"]}, DOI={10.1017/S026646740600349X}, abstractNote={All plant species face a fundamental reproductive trade-off: for a given investment in seed mass, they can produce either many small seeds or few large seeds. Whereas small seeds favour the germination of numerous seedlings, large seeds favour the survival of seedlings in the face of common stresses such as herbivory, drought or shade (Leishman et al. 2000). One mechanism explaining the better survival of large-seeded species is the seedling size effect (SSE) (Westoby et al. 1996): because seeds with large reserves result in bigger seedlings, seedlings from large-seeded species would have better access to light and/or to reliable water supply than seedlings from small-seeded species.}, journal={JOURNAL OF TROPICAL ECOLOGY}, author={Lahoreau, Gaelle and Barot, Sebastien and Gignoux, Jacques and Hoffmann, William A. and Setterfield, Samantha A. and Williams, Paul R.}, year={2006}, month={Nov}, pages={719–722} }
 @article{sternberg_bucci_franco_goldstein_hoffman_meinzer_moreira_scholz_2005, title={Long range lateral root activity by neo-tropical savanna trees}, volume={270}, ISSN={["0032-079X"]}, DOI={10.1007/s11104-004-1334-9}, number={1-2}, journal={PLANT AND SOIL}, author={Sternberg, LDL and Bucci, S and Franco, A and Goldstein, G and Hoffman, WA and Meinzer, FC and Moreira, MZ and Scholz, F}, year={2005}, month={Mar}, pages={169–178} }
 @article{hoffmann_silva_machado_bucci_scholz_goldstein_meinzer_2005, title={Seasonal leaf dynamics across a tree density gradient in a Brazilian savanna}, volume={145}, ISSN={["1432-1939"]}, DOI={10.1007/s00442-005-0129-x}, abstractNote={Interactions between trees and grasses that influence leaf area index (LAI) have important consequences for savanna ecosystem processes through their controls on water, carbon, and energy fluxes as well as fire regimes. We measured LAI, of the groundlayer (herbaceous and woody plants <1-m tall) and shrub and tree layer (woody plants >1-m tall), in the Brazilian cerrado over a range of tree densities from open shrub savanna to closed woodland through the annual cycle. During the dry season, soil water potential was strongly and positively correlated with grass LAI, and less strongly with tree and shrub LAI. By the end of the dry season, LAI of grasses, groundlayer dicots and trees declined to 28, 60, and 68% of mean wet-season values, respectively. We compared the data to remotely sensed vegetation indices, finding that field measurements were more strongly correlated to the enhanced vegetation index (EVI, r (2)=0.71) than to the normalized difference vegetation index (NDVI, r (2)=0.49). Although the latter has been more widely used in quantifying leaf dynamics of tropical savannas, EVI appears better suited for this purpose. Our ground-based measurements demonstrate that groundlayer LAI declines with increasing tree density across sites, with savanna grasses being excluded at a tree LAI of approximately 3.3. LAI averaged 4.2 in nearby gallery (riparian) forest, so savanna grasses were absent, thereby greatly reducing fire risk and permitting survival of fire-sensitive forest tree species. Although edaphic conditions may partly explain the larger tree LAI of forests, relative to savanna, biological differences between savanna and forest tree species play an important role. Overall, forest tree species had 48% greater LAI than congeneric savanna trees under similar growing conditions. Savanna and forest species play distinct roles in the structure and dynamics of savanna-forest boundaries, contributing to the differences in fire regimes, microclimate, and nutrient cycling between savanna and forest ecosystems.}, number={2}, journal={OECOLOGIA}, author={Hoffmann, WA and Silva, ER and Machado, GC and Bucci, SJ and Scholz, FG and Goldstein, G and Meinzer, FC}, year={2005}, month={Sep}, pages={307–316} }
 @article{hoffmann_franco_moreira_haridasan_2005, title={Specific leaf area explains differences in leaf traits between congeneric savanna and forest trees}, volume={19}, ISSN={["0269-8463"]}, DOI={10.1111/j.1365-2435.2005.01045.x}, abstractNote={Summary

1
Leaf traits are commonly associated with the life history, distribution and resource requirements of a species. To improve our understanding of the ecological and physiological differences between tropical savanna and forest trees, we compared leaf traits of species native to savanna and gallery (riverine) forests in the Cerrado region of central Brazil.

2
Congeneric species pairs from 14 different taxonomic families were studied, each with a savanna species and a forest species present at the study site. Only individuals growing in savanna conditions under full sun were studied. We measured foliar nutrients, δ13C, δ15N and specific leaf area (SLA: leaf area per unit leaf mass). We used phylogenetically independent contrasts to compare savanna and forest species and to test for correlations among species traits.

3
Overall, leaves of forest species had 17% higher N concentration, 32% higher P concentration, and 37% higher K concentration, despite growing in similar soils. Concentrations of all three elements were strongly and positively correlated with SLA.

4
Forest species had 52% greater SLA, on average, than savanna species, which accounts for the higher foliar nutrient concentrations of these species.

5
Savanna species had higher δ13C values than forest species, indicating higher water-use efficiency. The SLA was negatively correlated with δ13C, suggesting that SLA may also account for the higher water-use efficiency of savanna species.

6
There was no difference in foliar δ15N between savanna and forest species, but foliar δ15N was negatively correlated with soil pH.

7
These results contribute to recent studies showing that tropical savanna and forest species represent two distinct functional types, with large differences in ecology and physiology, that have important consequences for the dynamics of savanna–forest boundaries.}, number={6}, journal={FUNCTIONAL ECOLOGY}, author={Hoffmann, WA and Franco, AC and Moreira, MZ and Haridasan, M}, year={2005}, month={Dec}, pages={932–940} }
 @article{hoffmann_orthen_franco_2004, title={Constraints to seedling success of savanna and forest trees across the savanna-forest boundary}, volume={140}, ISSN={["1432-1939"]}, DOI={10.1007/s00442-004-1595-2}, number={2}, journal={OECOLOGIA}, author={Hoffmann, WA and Orthen, B and Franco, AC}, year={2004}, month={Jul}, pages={252–260} }
 @article{hoffmann_lucatelli_silva_azeuedo_marinho_albuquerque_lopes_moreira_2004, title={Impact of the invasive alien grass Melinis minutiflora at the savanna-forest ecotone in the Brazilian Cerrado}, volume={10}, ISSN={["1366-9516"]}, DOI={10.1111/j.1366-9516.2004.00063.x}, abstractNote={Exotic grasses are a serious threat to biodiversity in the cerrado savannas of central Brazil. Of particular concern is the possible role they may have in impeding tree regeneration at gallery (riverine) forest edges and increasing fire intensity, thereby driving gallery forest retreat. Here we quantify the effect of roads and distance from gallery forests on the abundance of the African grass Melinis minutiflora Beauv. and test for an effect of this species on woody plant regeneration and leaf area index. Melinis was present at approximately 70% of the sites near gallery forest edges, with its frequency declining sharply at greater distances from the edge. Melinis frequency was 2.8 times greater where roads were present nearby. Leaf area index (LAI) of the ground layer was 38% higher where Melinis was present than where it was absent. LAI was strongly correlated to fine fuel mass (r 2 = 0.80), indicating higher fuel loads where Melinis was present. The abundance of tree and shrub species in the ground layer was negatively related to LAI and to the presence of Melinis. The greater fuel accumulation and reduced tree regeneration caused by Melinis may cause a net reduction in forest area by increasing fire intensity at the gallery forest edge and slowing the rate of forest expansion.}, number={2}, journal={DIVERSITY AND DISTRIBUTIONS}, author={Hoffmann, WA and Lucatelli, VMPC and Silva, FJ and Azeuedo, INC and Marinho, MD and Albuquerque, AMS and Lopes, AD and Moreira, SP}, year={2004}, month={Mar}, pages={99–103} }
 @article{hoffmann_orthen_do nascimento_2003, title={Comparative fire ecology of tropical savanna and forest trees}, volume={17}, ISSN={["1365-2435"]}, DOI={10.1111/j.1365-2435.2003.00796.x}, abstractNote={Summary
1Fire is important in the dynamics of savanna–forest boundaries, often maintaining a balance between forest advance and retreat.
2We performed a comparative ecological study to understand how savanna and forest species differ in traits related to fire tolerance. We compared bark thickness, root and stem carbohydrates, and height of reproductive individuals within 10 congeneric pairs, each containing one savanna and one forest species.
3Bark thickness of savanna species averaged nearly three times that of forest species, thereby reducing the risk of stem death during fire. The allometric relationship between bark thickness and stem diameter differed between these two tree types, with forest species tending to have a larger allometric coefficient.
4The height of reproductive individuals of forest species averaged twice that of congeneric savanna species. This should increase the time necessary for forest species to reach reproductive size, thereby reducing their capacity to reach maturity in the time between consecutive fires.
5There was no difference in total non-structural carbohydrate content of stems or roots between savanna and forest species, though greater allocation to total root biomass by savanna species probably confers greater capacity to resprout following fire.
6These differences in fire-related traits may largely explain the greater capacity of savanna species to persist in the savanna environment.}, number={6}, journal={FUNCTIONAL ECOLOGY}, author={Hoffmann, WA and Orthen, B and Do Nascimento, PKV}, year={2003}, month={Dec}, pages={720–726} }
 @article{hoffmann_schroeder_jackson_2003, title={Regional feedbacks among fire, climate, and tropical deforestation}, volume={108}, number={D23}, journal={Journal of Geophysical Research. Atmospheres}, author={Hoffmann, W. A. and Schroeder, W. and Jackson, R. B.}, year={2003} }