@article{fischer_katul_noormets_poznikova_domec_orsag_zalud_trnka_king_2023, title={Merging flux-variance with surface renewal methods in the roughness sublayer and the atmospheric surface layer}, volume={342}, ISSN={["1873-2240"]}, DOI={10.1016/j.agrformet.2023.109692}, abstractNote={Two micrometeorological methods utilizing high-frequency sampled air temperature were tested against eddy covariance (EC) sensible heat flux (H) measurements at three sites representing agricultural, agro-forestry, and forestry systems. The two methods cover conventional and newly proposed forms of the flux-variance (FV) and surface renewal (SR) schemes of differing complexities. The sites represent measurements in surface, roughness, and roughness to surface transitional layers. Regression analyzes against EC show that the most reliable FV and SR forms estimate H with slopes within ±10% from unity and coefficient of determination R2>0.9 across all the three sites. The best performance of both FV and SR was found at the agricultural site with measurements well within the surface layer, while the worst was found for the tall forest with measurements within the roughness sublayer where its thickness needed to be additionally estimated. The main variable driving H in FV is the temperature variance, whereas in SR, it is the geometry of ramp-like structures. Since these structures are also responsible for most of the temperature variance, a novel FV-SR approach emerging from combining the methods is proposed and evaluated against EC measurements and conventional FV and SR schemes. The proposed FV-SR approach requiring only a single fast response thermocouple is potentially independent of calibration and ameliorates some of the theoretical objections that arise when combining ramp statistics with similarity arguments. The combination of methods also provides new insights into the contribution of coherent structures to the temperature variance and its dependence on atmospheric stratification. Other potential utility of the new method is to include it in multi-tool assessments of surface energy fluxes, since a convergence or divergence of the results has a high diagnostic value.}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Fischer, Milan and Katul, Gabriel and Noormets, Asko and Poznikova, Gabriela and Domec, Jean-Christophe and Orsag, Matej and Zalud, Zdenek and Trnka, Miroslav and King, John S.}, year={2023}, month={Nov} }
 @article{aguilos_brown_minick_fischer_ile_hardesty_kerrigan_noormets_king_2021, title={Millennial-Scale Carbon Storage in Natural Pine Forests of the North Carolina Lower Coastal Plain: Effects of Artificial Drainage in a Time of Rapid Sea Level Rise}, volume={10}, ISSN={2073-445X}, url={http://dx.doi.org/10.3390/land10121294}, DOI={10.3390/land10121294}, abstractNote={Coastal forested wetlands provide important ecosystem services along the southeastern region of the United States, but are threatened by anthropogenic and natural disturbances. Here, we examined the species composition, mortality, aboveground biomass, and carbon content of vegetation and soils in natural pine forests of the lower coastal plain in eastern North Carolina, USA. We compared a forest clearly in decline (termed “ghost forest”) adjacent to a roadside canal that had been installed as drainage for a road next to an adjacent forest subject to “natural” hydrology, unaltered by human modification (termed “healthy forest”). We also assessed how soil organic carbon (SOC) accumulation changed over time using 14C radiocarbon dating of wood sampled at different depths within the peat profile. Our results showed that the ghost forest had a higher tree density at 687 trees ha−1, and was dominated by swamp bays (Persea palustric), compared to the healthy forest, which had 265 trees ha−1 dominated by pond pine (Pinus serotina Michx). Overstory tree mortality of the ghost forest was nearly ten times greater than the healthy forest (p < 0.05), which actually contributed to higher total aboveground biomass (55.9 ± 12.6 Mg C ha−1 vs. 27.9 ± 8.7 Mg ha−1 in healthy forest), as the dead standing tree biomass (snags) added to that of an encroaching woody shrub layer during ecosystem transition. Therefore, the total aboveground C content of the ghost forest, 33.98 ± 14.8 Mg C ha−1, was higher than the healthy forest, 24.7 ± 5.2 Mg C ha−1 (p < 0.05). The total SOC stock down to a 2.3 m depth in the ghost forest was 824.1 ± 46.2 Mg C ha−1, while that of the healthy forest was 749.0 ± 170.5 Mg C ha−1 (p > 0.05). Carbon dating of organic sediments indicated that, as the sample age approaches modern times (surface layer year 2015), the organic soil accumulation rate (1.11 to 1.13 mm year−1) is unable to keep pace with the estimated rate of recent sea level rise (2.1 to 2.4 mm year−1), suggesting a causative relationship with the ecosystem transition occurring at the site. Increasing hydrologic stress over recent decades appears to have been a major driver of ecosystem transition, that is, ghost forest formation and woody shrub encroachment, as indicated by the far higher overstory tree mortality adjacent to the drainage ditch, which allows the inland propagation of hydrologic/salinity forcing due to SLR and extreme storms. Our study documents C accumulation in a coastal wetland over the past two millennia, which is now threatened due to the recent increase in the rate of SLR exceeding the natural peat accumulation rate, causing an ecosystem transition with unknown consequences for the stored C; however, much of it will eventually be returned to the atmosphere. More studies are needed to determine the causes and consequences of coastal ecosystem transition to inform the modeling of future coastal wetland responses to environmental change and the estimation of regional terrestrial C stocks and flux.}, number={12}, journal={Land}, publisher={MDPI AG}, author={Aguilos, Maricar and Brown, Charlton and Minick, Kevan and Fischer, Milan and Ile, Omoyemeh J. and Hardesty, Deanna and Kerrigan, Maccoy and Noormets, Asko and King, John}, year={2021}, month={Nov}, pages={1294} }
 @article{minick_mitra_li_fischer_aguilos_prajapati_noormets_king_2021, title={Wetland microtopography alters response of potential net CO2 and CH4 production to temperature and moisture: Evidence from a laboratory experiment}, volume={402}, ISSN={["1872-6259"]}, url={https://doi.org/10.1016/j.geoderma.2021.115367}, DOI={10.1016/j.geoderma.2021.115367}, abstractNote={Coastal wetlands store significant amounts of carbon (C) belowground, which may be altered through effects of rising temperature and changing hydrology on CO2 and CH4 fluxes and related microbial activities. Wetland microtopography (hummock-hollow) also plays a critical role in mediating plant growth, microbial activity, and thus cycling of C and nutrients and may interact with rising seas to influence coastal wetland C dynamics. Recent evidence suggests that CH4 production in oxygenated surface soils of freshwater wetlands may contribute substantially to global CH4 production, but comprehensive studies linking potential CH4 production to environmental and microbial variables in temperate freshwater forested wetlands are lacking. This study investigated effects of temperature, moisture, and microtopography on potential net CO2 and CH4 production and extracellular enzyme activity (β-glucosidase, xylosidase, phenol oxidase, and peroxidase) in peat soils collected from a freshwater forested wetland in coastal North Carolina, USA. Soils were retrieved from three microsites (hummock, hollow, and subsurface peat soils (approximately 20–40 cm below surface)) and incubated at two temperatures (27 °C and 32 °C) and soil water contents (65% and 100% water holding capacity (WHC)). Hummocks had the highest cumulative potential net CO2 (13.7 ± 0.90 mg CO2-C g soil−1) and CH4 (1.8 ± 0.42 mg CH4-C g soil−1) production and enzyme activity, followed by hollows (8.7 ± 0.91 mg CO2-C g soil−1 and 0.5 ± 0.12 mg CH4-C g soil−1) and then subsurface soils (5.7 ± 0.70 mg CO2-C g soil−1 and 0.04 ± 0.019 mg CH4-C g soil−1). Fully saturated soils had lower potential net CO2 production (50–80%) and substantially higher potential net CH4 production compared to non-saturated soils (those incubated at 65% WHC). Soils incubated at 32 °C increased potential net CO2 (24–34%) and CH4 (56–404%) production under both soil moisture levels compared to those incubated at 27 °C. The Q10 values for potential net CO2 and CH4 production ranged from 1.5 to 2.3 and 3.3–8.8, respectively, and did not differ between any microsites or soil water content. Enrichment of δ13CO2-C was found in saturated soils from all microsites (−24.4 to − 29.7 ‰) compared to non-saturated soils (−31.1 to − 32.4 ‰), while δ13CH4-C ranged from −62 to −55‰ in saturated soils. Together, the CO2 and CH4 δ13C data suggest that acetoclastic methanogenesis is an important pathway for CH4 production in these wetlands. A positive relationship (Adj. R2 = 0.40) between peroxidase activity and CH4 production was also found, indicating that peroxidase activity may be important in providing fermented C substrates to acetoclastic methanogenic communities and contribute to anaerobic C mineralization. These results suggest that changes in temperature and hydrology could stimulate CO2 and CH4 emissions from surface hummock soils, and to a lesser extent from hollow soils, and provide preliminary evidence that hummocks may be a spatially important and unrecognized hotspot for CH4 production.}, journal={GEODERMA}, author={Minick, Kevan J. and Mitra, Bhaskar and Li, Xuefeng and Fischer, Milan and Aguilos, Maricar and Prajapati, Prajaya and Noormets, Asko and King, John S.}, year={2021}, month={Nov} }
 @article{poznikova_fischer_kesteren_orsag_hlavinka_zalud_trnka_2018, title={Quantifying turbulent energy fluxes and evapotranspiration in agricultural field conditions: A comparison of micrometeorological methods}, volume={209}, ISSN={["1873-2283"]}, DOI={10.1016/j.agwat.2018.07.041}, abstractNote={Accurate estimation of energy fluxes and evapotranspiration (ET) in agricultural systems is critically needed, especially for water resource sustainability, soil moisture monitoring and irrigation. Numerous micrometeorological methods have become commercially available. Considering the eventual trade-off between cost and accuracy, it is important to evaluate these methods to provide recommendations for practical purposes. Therefore, we tested five different techniques at one field in the region of Central Europe dominated by rainfed farming but suffers from drought spells. In an intensive campaign, we used eddy covariance (EC), large aperture and surface layer scintillometers, the Bowen ratio energy balance (BREB), and the surface renewal (SR) methods to estimate the sensible (H) and latent (λET) heat fluxes of winter wheat and bare soil with harvest residues during two months in summer 2015. At the half-hourly level, the methods showed varying agreement under different field conditions. While H estimated by EC and scintillometry agreed well, there was an underestimation of λET by EC compared to the other methods, most likely due to energy balance non-closure. The λET estimated by the BREB method showed good agreement with the λET obtained by scintillometry when the Bowen ratio (β) was high and with the λET obtained by EC when β → 0. Our study confirmed good reliability of scintillometers across wide range of meteorological conditions. Although the SR method provided the most inferior agreement with other methods at half-hourly basis, it was deemed to be valuable when longer averaging periods were used. Over the entire experiment, mean daily ET estimated by scintillometry (2.6 mm d−1), BREB (2.3 mm d−1), and SR (2.9 mm d−1) showed reasonable agreement while EC (1.6 mm d−1) significantly underestimated. This indicates that low cost methods (BREB and SR) are sufficient for water management purposes when a daily and longer time scales are important. Further, parallel deploying of BREB and SR can provide additional diagnostics and increase the confidence in ET estimates.}, journal={AGRICULTURAL WATER MANAGEMENT}, author={Poznikova, Gabriela and Fischer, Milan and Kesteren, Bram and Orsag, Matej and Hlavinka, Petr and Zalud, Zdenek and Trnka, Miroslav}, year={2018}, month={Oct}, pages={249–263} }
 @article{fischer_kelley_ward_boone_ashley_domec_williamson_king_2017, title={A critical analysis of species selection and high vs. low-input silviculture on establishment success and early productivity of model short-rotation wood-energy cropping systems}, volume={98}, ISSN={["1873-2909"]}, DOI={10.1016/j.biombioe.2017.01.027}, abstractNote={Most research on bioenergy short rotation woody crops (SRWC) has been dedicated to the genera Populus and Salix. These species generally require relatively high-input culture, including intensive weed competition control, which increases costs and environmental externalities. Widespread native early successional species, characterized by high productivity and good coppicing ability, may be better adapted to local environmental stresses and therefore could offer alternative low-input bioenergy production systems. To test this concept, we established a three-year experiment comparing a widely-used hybrid poplar (Populus nigra × P. maximowiczii, clone ‘NM6’) to two native species, American sycamore (Platanus occidentalis L.) and tuliptree (Liriodendron tulipifera L.) grown under contrasting weed and pest control at a coastal plain site in eastern North Carolina, USA. Mean cumulative aboveground wood production was significantly greater in sycamore, with yields of 46.6 Mg ha−1 under high-inputs and 32.7 Mg ha−1 under low-input culture, which rivaled the high-input NM6 yield of 32.9 Mg ha−1. NM6 under low-input management provided noncompetitive yield of 6.2 Mg ha−1. Sycamore also showed superiority in survival, biomass increment, weed resistance, treatment convergence, and within-stand uniformity. All are important characteristics for a bioenergy feedstock crop species, leading to reliable establishment and efficient biomass production. Poor performance in all traits was found for tuliptree, with a maximum yield of 1.2 Mg ha−1, suggesting this native species is a poor choice for SRWC. We conclude that careful species selection beyond the conventionally used genera may enhance reliability and decrease negative environmental impacts of the bioenergy biomass production sector.}, journal={BIOMASS & BIOENERGY}, author={Fischer, M. and Kelley, A. M. and Ward, E. J. and Boone, J. D. and Ashley, E. M. and Domec, J. -C. and Williamson, J. C. and King, J. S.}, year={2017}, month={Mar}, pages={214–227} }
 @article{domec_ashley_fischer_noormets_boone_williamson_king_2017, title={Productivity, Biomass Partitioning, and Energy Yield of Low-Input Short-Rotation American Sycamore (Platanus occidentalis L.) Grown on Marginal Land: Effects of Planting Density and Simulated Drought}, volume={10}, ISSN={["1939-1242"]}, DOI={10.1007/s12155-017-9852-5}, number={3}, journal={BIOENERGY RESEARCH}, author={Domec, Jean-Christophe and Ashley, Elissa and Fischer, Milan and Noormets, Asko and Boone, Jameson and Williamson, James C. and King, John S.}, year={2017}, month={Sep}, pages={903–914} }
 @article{tian_cacho_youssef_chescheir_fischer_nettles_king_2017, title={Switchgrass growth and pine-switchgrass interactions in established intercropping systems}, volume={9}, ISSN={["1757-1707"]}, DOI={10.1111/gcbb.12381}, abstractNote={Abstract}, number={5}, journal={GLOBAL CHANGE BIOLOGY BIOENERGY}, author={Tian, Shiying and Cacho, Julian F. and Youssef, Mohamed A. and Chescheir, George M. and Fischer, Milan and Nettles, Jami E. and King, John S.}, year={2017}, month={May}, pages={845–857} }
 @article{trnka_fischer_bartosova_orsag_kyncl_ceulemans_king_buntgen_2016, title={Potential and limitations of local tree ring records in estimating a priori the growth performance of short-rotation coppice plantations}, volume={92}, ISSN={["1873-2909"]}, DOI={10.1016/j.biombioe.2016.05.026}, abstractNote={As bioenergy plantations are a relatively new phenomenon, long-term experimental data on their productivity and tolerance to environmental stress that provides a robust framework for site selection and potential productivity assessment is still lacking. To address this need, we developed a method to correlate the productivity of bioenergy plantations with local climate using tree-ring chronologies. Tree-ring width from 37 Populus nigra (age > 115 y) and 368 poplar hybrid (Populus nigra × Populus maximowiczii) (9–12 y) individuals were collected and analyzed at demonstration sites in the Czech Republic. The growth of mature, naturally grown solitary native trees and young congeneric hybrids grown in high density (∼10,000 ha−1) showed statistically significant correlations (r = 0.71, p < 0.05). Further, we found significant (p < 0.05) and consistent growth responses to changes in key seasonal climatic parameters (e.g., mean air temperature, number of dry days or cumulative heat sum (degree-days) during the growing season) for both natives and their hybrids. The analysis of climate conditions and the tree-ring records revealed a gradual change of climatic conditions since the 1930s, positively affecting poplar growth and indicated that longer rather than shorter harvest cycles are preferable to ensure stable yields at our experimental site.}, journal={BIOMASS & BIOENERGY}, author={Trnka, Miroslav and Fischer, Milan and Bartosova, Lenka and Orsag, Matej and Kyncl, Tomas and Ceulemans, Reinhart and King, John and Buntgen, Ulf}, year={2016}, month={Sep}, pages={12–19} }
 @inproceedings{tripathi_fischer_trnka_orsag_vanbeveren_marek_2015, title={Leaf area index development and radiation use efficiency of a poplar short rotation coppice culture}, booktitle={Global Change: A Complex Challenge}, author={Tripathi, A. M. and Fischer, M. and Trnka, M. and Orsag, M. and Vanbeveren, S. P. P. and Marek, M. V.}, year={2015}, pages={90–93} }
 @inproceedings{orsag_fischer_tripathi_zalud_trnka_2015, title={Long-term productivity of short rotation coppice under decreased soil water availability}, booktitle={Global Change: A Complex Challenge}, author={Orsag, M. and Fischer, M. and Tripathi, A. M. and Zalud, Z. and Trnka, M.}, year={2015}, pages={98–101} }
 @inproceedings{poznikova_fischer_orsag_trnka_zalud_2015, title={The Bowen Ratio/Energy Balance method and detailed temperature profile measurements to improve data quality control}, booktitle={Global Change: A Complex Challenge}, author={Poznikova, G. and Fischer, M. and Orsag, M. and Trnka, M. and Zalud, Z.}, year={2015}, pages={62–65} }