@article{robbins_xu_jonko_chitra-tarak_fettig_costanza_mortenson_aukema_kueppers_scheller_2023, title={Carbon stored in live ponderosa pines in the Sierra Nevada will not return to pre-drought (2012) levels during the 21st century due to bark beetle outbreaks}, volume={11}, ISSN={["2296-665X"]}, DOI={10.3389/fenvs.2023.1112756}, abstractNote={Outbreaks of several bark beetle species can develop rapidly in response to drought and may result in large transfers of carbon (C) stored in live trees to C stored in dead trees (10s of Tg C yr -1 in the western U.S. alone), which over time will be released back to the atmosphere. The western pine beetle (WPB) outbreak incited by the 2012–2015 mega-drought in the Sierra Nevada, California, U.S., could portend more frequent and/or severe bark beetle outbreaks as the temperature warms and drought frequency and intensity increase in the future. However, changes in the frequency and/or severity (resultant levels of host tree mortality) of beetle outbreaks are difficult to predict as outbreaks are complex with non-linear and eruptive processes primarily driven by interactions among beetle populations, the demography of hosts and other tree species, and climate and weather. Using an insect phenology and tree defense model, we projected the future likelihood of WPB outbreaks in the Sierra Nevada with climate drivers from different Earth System Models. Our goal was to understand how host (ponderosa pine, PIPO) recovery and future warming and drought affect the frequency and severity of WPB outbreaks and their C consequences. Our projections suggested that by 2100 the C stored in live PIPO (mean: 1.98 kg C m -2, 95% CI: 1.74–2.21 kg C m -2 ) will not return to levels that occurred before the 2012–2015 drought (2012: ∼2.30 kg C m -2 ) due to future WPB outbreaks. However, differences in climate models indicate a wide range of possible WPB outbreak frequencies and severities. Our results suggest that total plot basal area is the most significant factor in the mortality rate of PIPO by WPB in any given year, followed by drought severity and temperature. High levels of host basal area, higher temperature, and extreme drought all contribute to the frequency and severity of future WPB outbreaks. While PIPO basal area may decline under increased drought and warming, limiting high-stand basal area (>60 m 2 ha -1 ) may reduce the severity of future WPB outbreaks in the Sierra Nevada.}, journal={FRONTIERS IN ENVIRONMENTAL SCIENCE}, author={Robbins, Zachary J. and Xu, Chonggang and Jonko, Alex and Chitra-Tarak, Rutuja and Fettig, Christopher J. and Costanza, Jennifer and Mortenson, Leif A. and Aukema, Brian H. and Kueppers, Lara M. and Scheller, Robert M.}, year={2023}, month={Mar} }
 @article{robbins_loudermilk_reilly_o'brien_jones_gerstle_scheller_2022, title={Delayed fire mortality has long-term ecological effects across the Southern Appalachian landscape}, volume={13}, ISSN={["2150-8925"]}, url={https://doi.org/10.1002/ecs2.4153}, DOI={10.1002/ecs2.4153}, abstractNote={Fire is a critical ecological process to the forests of the Southern Appalachians. Where fire was excluded from forest types that historically burned frequently, unanticipated changes can occur when fire is reintroduced. For example, the development of new fuel characteristics can change the patterns of fire mortality and associated ecological responses. To test the fire effects of delayed fire mortality (mortality initiated by fire that occurs subsequent to the fire year) in the Southern Appalachians, USA, we developed a fire-effects model using both field studies and remote sensing. We then simulated these effects at a landscape scale to estimate broader ecological effects. Fire-effects models that accounted for delayed mortality increased landscape biomass removed annually (~23%) and increased the number of sites with high light conditions (leaf area index < 4) when compared to simulations that only account for immediate mortality. While delayed mortality occurred across species and age classes, it was especially prevalent among older trees (>100 years old) and fire-resistant species (Quercus spp.). Overall, regeneration (trees <20 years old) changed very little, even with the inclusion of delayed mortality. This evidence suggests that, even when accounting for delayed mortality, individual fires are unlikely to shift the landscape composition toward the conditions of forests prior to fire exclusion and may even increase mesophication long term due to the loss of overstory dominant xeric trees.}, number={6}, journal={ECOSPHERE}, publisher={Wiley}, author={Robbins, Zachary J. and Loudermilk, E. Louise and Reilly, Matthew J. and O'Brien, Joseph J. and Jones, Kate and Gerstle, Christopher T. and Scheller, Robert M.}, year={2022}, month={Jun} }
 @article{mozelewski_robbins_scheller_2022, title={Forecasting the influence of conservation strategies on landscape connectivity}, volume={6}, ISSN={["1523-1739"]}, DOI={10.1111/cobi.13904}, abstractNote={Maintaining and enhancing landscape connectivity reduces biodiversity declines due to habitat fragmentation. Uncertainty remains, however, about the effectiveness of conservation for enhancing connectivity for multiple species on dynamic landscapes, especially over long time horizons. We forecasted landscape connectivity from 2020 to 2100 under four common conservation land-acquisition strategies: acquiring the lowest cost land, acquiring land clustered around already established conservation areas, acquiring land with high geodiversity characteristics, and acquiring land opportunistically. We used graph theoretic metrics to quantify landscape connectivity across these four strategies, evaluating connectivity for four ecologically relevant species guilds that represent endpoints along a spectrum of vagility and habitat specificity: long- versus short-distance dispersal ability and habitat specialists versus generalists. We applied our method to central North Carolina and incorporated landscape dynamics, including forest growth, succession, disturbance, and management. Landscape connectivity improved for specialist species under all conservation strategies employed, although increases were highly variable across strategies. For generalist species, connectivity improvements were negligible. Overall, clustering the development of new protected areas around land already designated for conservation yielded the largest improvements in connectivity; increases were several orders of magnitude beyond current landscape connectivity for long- and short-distance dispersing specialist species. Conserving the lowest cost land contributed the least to connectivity. Our approach provides insight into the connectivity contributions of a suite of conservation alternatives prior to on-the-ground implementation and, therefore, can inform connectivity planning to maximize conservation benefit.Pronóstico de la Influencia de las Estrategias de Conservación sobre la Conectividad del Paisaje Resumen El mantenimiento y la mejora de la conectividad de paisaje reduce las declinaciones de biodiversidad causadas por la fragmentación del hábitat. Sin embargo, todavía existe incertidumbre sobre lo efectiva que es la conservación para la mejora de la conectividad para múltiples especies en paisajes dinámicos, especialmente durante periodos largos. Pronosticamos la conectividad de paisaje desde el 2020 hasta el 2100 bajo cuatro estrategias comunes de adquisición de tierras para conservación: adquisición de las tierras más baratas, adquisición de conjuntos de tierras adyacentes a áreas de conservación ya establecidas, adquisición de tierras con una gran diversidad de características geográficas, y adquisición oportunista de tierras. Después usamos medidas de teoría de grafos para cuantificar la conectividad de paisaje en estas cuatro estrategias y para evaluar la conectividad de cuatro gremios de especies con relevancia ecológica que representan los puntos finales en un espectro de movilidad y especificidad de hábitat: habilidad de dispersión de distancia corta versus larga y especialistas versus generalistas de hábitat. Aplicamos nuestro método en el centro de Carolina del Norte e incorporamos las dinámicas de paisaje, incluyendo el crecimiento, sucesión, alteración y gestión forestales. La conectividad del paisaje mejoró para las especies especialistas bajo todas las estrategias de conservación que se usaron, aunque los incrementos fueron muy variables según la estrategia. Para las especies generalistas, las mejoras en la conectividad fueron insignificantes. En general, agrupar al desarrollo de nuevas áreas protegidas alrededor de tierras ya designadas a la conservación produjo la mayor cantidad de mejoras en la conectividad; los incrementos estuvieron varias magnitudes más allá de la conectividad actual del paisaje para las especies especialistas con dispersión de corta y larga distancia. La conservación de las tierras más baratas contribuyó a la menor conectividad. Nuestra estrategia proporciona información sobre las contribuciones de conectividad de un conjunto de alternativas de conservación previas la implementación in situ y por lo tanto puede servir para orientar la planeación y maximizar el beneficio de conservación.【摘要】维持和提高景观连接度可以减少因生境破碎化导致的生物多样性丧失。然而, 在动态的景观中提高多物种连接度的保护有效性仍存在不确定性, 特别是在较长的时间范围内。本研究预测了 4 种常见的保护性土地征用策略在 2020 年到 2100 年的景观连接度, 这些策略包括征用成本最低的土地、征用已有保护区周围的土地、征用地理多样性高的土地, 以及随机征用土地。我们使用图论指标量化了这 4 种策略的景观连接度, 评估了 4 个有生态价值的物种种群的连接度, 这些物种代表了不同的扩散能力和栖息地特异性:从长距离扩散到短距离扩散, 以及从栖息地专性种到广适种。我们将该方法应用于北卡罗来纳州中部, 并纳入了景观动态, 包括森林生长、演替、干扰和管理。我们发现, 专性种的景观连接度在所有保护策略下都得到了改善, 尽管不同策略之间的效果存在差异。而广适种的连接度则几乎没有提高。总的来说, 将新的保护区集中在已经建立的保护地周围, 可以最大限度地提高连接度;长距离和短距离扩散的专性种连接度的增加比目前的景观连接度要高出几个数量级。保护成本最低的土地对连接度的贡献最小。我们的方法为一系列保护替代方案实施前的连接度贡献评估提供了见解, 因此可以为连接度规划提供信息, 使保护效益最大化。【翻译: 胡怡思; 审校: 聂永刚】.}, journal={CONSERVATION BIOLOGY}, author={Mozelewski, Tina G. and Robbins, Zachary J. and Scheller, Robert M.}, year={2022}, month={Jun} }
 @article{buotte_koven_xu_shuman_goulden_levis_katz_ding_ma_robbins_et al._2021, title={Capturing functional strategies and compositional dynamics in vegetation demographic models}, volume={18}, ISSN={["1726-4189"]}, DOI={10.5194/bg-18-4473-2021}, abstractNote={Abstract. Plant community composition influences carbon, water, and energy fluxes at regional to global scales. Vegetation demographic models (VDMs) allow investigation of the effects of changing climate and disturbance regimes on vegetation composition and fluxes. Such investigation requires that the models can accurately resolve these feedbacks to simulate realistic composition. Vegetation in VDMs is composed of plant functional types (PFTs), which are specified according to plant traits. Defining PFTs is challenging due to large variability in trait observations within and between plant types and a lack of understanding of model sensitivity to these traits. Here we present an approach for developing PFT parameterizations that are connected to the underlying ecological processes determining forest composition in the mixed-conifer forest of the Sierra Nevada of California, USA. We constrain multiple relative trait values between PFTs, as opposed to randomly sampling within the range of observations. An ensemble of PFT parameterizations are then filtered based on emergent forest properties meeting observation-based ecological criteria under alternate disturbance scenarios. A small ensemble of alternate PFT parameterizations is identified that produces plausible forest composition and demonstrates variability in response to disturbance frequency and regional environmental variation. Retaining multiple PFT parameterizations allows us to quantify the uncertainty in forest responses due to variability in trait observations. Vegetation composition is a key emergent outcome from VDMs and our methodology provides a foundation for robust PFT parameterization across ecosystems.}, number={14}, journal={BIOGEOSCIENCES}, author={Buotte, Polly C. and Koven, Charles D. and Xu, Chonggang and Shuman, Jacquelyn K. and Goulden, Michael L. and Levis, Samuel and Katz, Jessica and Ding, Junyan and Ma, Wu and Robbins, Zachary and et al.}, year={2021}, month={Jul}, pages={4473–4490} }
 @article{vakili_shakeri_motahari_farahani_robbins_scheller_2021, title={Resistance and Resilience of Hyrcanian Mixed Forests Under Natural and Anthropogenic Disturbances}, volume={4}, ISSN={["2624-893X"]}, DOI={10.3389/ffgc.2021.640451}, abstractNote={Biological disturbances are integral to forest ecosystems and have pronounced effects on forest resistance, resilience, and diversity. The Hyrcanian mixed forest, in northern Iran, is at risk of declining resistance, resilience, and diversity due to ongoing pressure from land use change, harvesting, and biological disturbances. We analyzed the resistance and resilience of this area under two biological disturbances (i.e., oak charcoal fungus, Biscogniauxia mediterranea , and alder leaf beetle, Galerucella lineola ) and in concert with proposed harvesting. We used a simulation modeling approach whereby we simulated 12 combinations of biological disturbances and harvesting scenarios using the LANDIS-II landscape change model. We estimated the correlation between forest resistance and resilience and tree species diversity to harvesting and biological disturbance. We analyzed the full species composition and age class for 30 and 100 years after disturbances in order to assess resistance as the change in species composition over time. We considered resilience as the ability to recover from a disturbance back to a similar initial state. Results indicate a positive effect of biological disturbances and harvesting on diversity. Our simulations resulted in a negative relationship between diversity-resistance and diversity-resilience within high diversity areas. Our simulation of the Hyrcanian forest reveals that harvesting and biological disturbances, as tested, fulfill the goal of maintaining forest diversity. However, increasing diversity does not always follow by increasing forest resistance and resilience. Scenarios with oak charcoal fungus, both with and without harvesting indicate the lowest decrease in resilient and resistant.}, journal={FRONTIERS IN FORESTS AND GLOBAL CHANGE}, author={Vakili, Mehdi and Shakeri, Zahed and Motahari, Saeed and Farahani, Maryam and Robbins, Zachary James and Scheller, Robert M.}, year={2021}, month={Jul} }
 @article{robbins_xu_aukema_buotte_chitra-tarak_fettig_goulden_goodsman_hall_koven_et al._2021, title={Warming increased bark beetle-induced tree mortality by 30% during an extreme drought in California}, volume={10}, ISSN={["1365-2486"]}, DOI={10.1111/gcb.15927}, abstractNote={Quantifying the responses of forest disturbances to climate warming is critical to our understanding of carbon cycles and energy balances of the Earth system. The impact of warming on bark beetle outbreaks is complex as multiple drivers of these events may respond differently to warming. Using a novel model of bark beetle biology and host tree interactions, we assessed how contemporary warming affected western pine beetle (Dendroctonus brevicomis) populations and mortality of its host, ponderosa pine (Pinus ponderosa), during an extreme drought in the Sierra Nevada, California, United States. When compared with the field data, our model captured the western pine beetle flight timing and rates of ponderosa pine mortality observed during the drought. In assessing the influence of temperature on western pine beetles, we found that contemporary warming increased the development rate of the western pine beetle and decreased the overwinter mortality rate of western pine beetle larvae leading to increased population growth during periods of lowered tree defense. We attribute a 29.9% (95% CI: 29.4%-30.2%) increase in ponderosa pine mortality during drought directly to increases in western pine beetle voltinism (i.e., associated with increased development rates of western pine beetle) and, to a much lesser extent, reductions in overwintering mortality. These findings, along with other studies, suggest each degree (°C) increase in temperature may have increased the number of ponderosa pine killed by upwards of 35%-40% °C-1 if the effects of compromised tree defenses (15%-20%) and increased western pine beetle populations (20%) are additive. Due to the warming ability to considerably increase mortality through the mechanism of bark beetle populations, models need to consider climate's influence on both host tree stress and the bark beetle population dynamics when determining future levels of tree mortality.}, journal={GLOBAL CHANGE BIOLOGY}, author={Robbins, Zachary J. and Xu, Chonggang and Aukema, Brian H. and Buotte, Polly C. and Chitra-Tarak, Rutuja and Fettig, Christopher J. and Goulden, Michael L. and Goodsman, Devin W. and Hall, Alexander D. and Koven, Charles D. and et al.}, year={2021}, month={Oct} }