Browsing by Author "Starr, Gregory"
Now showing 1 - 14 of 14
Results Per Page
Sort Options
Item Carbon Dynamics of Pinus palustris Ecosystems Following Drought(MDPI, 2016-04-29) Starr, Gregory; Staudhammer, Christina L.; Wiesner, Susanne; Kunwor, Sujit; Loescher, Henry W.; Baron, Andres F.; Whelan, Andrew; Mitchell, Robert J.; Boring, Lindsay; University of Alabama Tuscaloosa; University of Colorado System; University of Colorado BoulderDrought can affect forest structure and function at various spatial and temporal scales. Forest response and recovery from drought may be a result of position within landscape. Longleaf pine forests in the United States have been observed to reduce their carbon sequestration capacity during drought. We collected eddy covariance data at the ends of an edaphic longleaf pine gradient (xeric and mesic sites) over seven years; two years of normal rainfall were followed by 2.5 years of drought, then 2.5 years of normal or slightly above-average rainfall. Drought played a significant role in reducing the physiological capacity of the sites and was compounded when prescribed fire occurred during the same periods. The mesic site has a 40% greater basal area then the xeric site, which accounts for its larger sequestration capacity; however, both sites show the same range of variance in fluxes over the course of the study. Following drought, both sites became carbon sinks. However, the xeric site had a longer carry-over effect and never returned to pre-drought function. Although this study encompassed seven years, we argue that longer studies with greater spatial variance must be undertaken to develop a more comprehensive understanding of forest response to changing climate.Item Characterizing Growing Season Length of Subtropical Coniferous Forests with a Phenological Model(MDPI, 2021) Gong, Yuan; Staudhammer, Christina L.; Wiesner, Susanne; Starr, Gregory; Zhang, Yinlong; Nanjing Forestry University; University of Alabama Tuscaloosa; University of Wisconsin System; University of Wisconsin MadisonUnderstanding plant phenological change is of great concern in the context of global climate change. Phenological models can aid in understanding and predicting growing season changes and can be parameterized with gross primary production (GPP) estimated using the eddy covariance (EC) technique. This study used nine years of EC-derived GPP data from three mature subtropical longleaf pine forests in the southeastern United States with differing soil water holding capacity in combination with site-specific micrometeorological data to parameterize a photosynthesis-based phenological model. We evaluated how weather conditions and prescribed fire led to variation in the ecosystem phenological processes. The results suggest that soil water availability had an effect on phenology, and greater soil water availability was associated with a longer growing season (LOS). We also observed that prescribed fire, a common forest management activity in the region, had a limited impact on phenological processes. Dormant season fire had no significant effect on phenological processes by site, but we observed differences in the start of the growing season (SOS) between fire and non-fire years. Fire delayed SOS by 10 d +/- 5 d (SE), and this effect was greater with higher soil water availability, extending SOS by 18 d on average. Fire was also associated with increased sensitivity of spring phenology to radiation and air temperature. We found that interannual climate change and periodic weather anomalies (flood, short-term drought, and long-term drought), controlled annual ecosystem phenological processes more than prescribed fire. When water availability increased following short-term summer drought, the growing season was extended. With future climate change, subtropical areas of the Southeastern US are expected to experience more frequent short-term droughts, which could shorten the region's growing season and lead to a reduction in the longleaf pine ecosystem's carbon sequestration capacity.Item Cyclic Occurrence of Fire and Its Role in Carbon Dynamics along an Edaphic Moisture Gradient in Longleaf Pine Ecosystems(PLOS, 2013-01-13) Whelan, Andrew; Mitchell, Robert; Staudhammer, Christina; Starr, Gregory; University of Alabama TuscaloosaFire regulates the structure and function of savanna ecosystems, yet we lack understanding of how cyclic fire affects savanna carbon dynamics. Furthermore, it is largely unknown how predicted changes in climate may impact the interaction between fire and carbon cycling in these ecosystems. This study utilizes a novel combination of prescribed fire, eddy covariance (EC) and statistical techniques to investigate carbon dynamics in frequently burned longleaf pine savannas along a gradient of soil moisture availability (mesic, intermediate and xeric). This research approach allowed us to investigate the complex interactions between carbon exchange and cyclic fire along the ecological amplitude of longleaf pine. Over three years of EC measurement of net ecosystem exchange (NEE) show that the mesic site was a net carbon sink (NEE = -2.48 tonnes C ha 21), while intermediate and xeric sites were net carbon sources (NEE = 1.57 and 1.46 tonnes C ha(-1), respectively), but when carbon losses due to fuel consumption were taken into account, all three sites were carbon sources (10.78, 7.95 and 9.69 tonnes C ha(-1) at the mesic, intermediate and xeric sites, respectively). Nonetheless, rates of NEE returned to pre-fire levels 1-2 months following fire. Consumption of leaf area by prescribed fire was associated with reduction in NEE post-fire, and the system quickly recovered its carbon uptake capacity 30-60 days post fire. While losses due to fire affected carbon balances on short time scales (instantaneous to a few months), drought conditions over the final two years of the study were a more important driver of net carbon loss on yearly to multi-year time scales. However, longer-term observations over greater environmental variability and additional fire cycles would help to more precisely examine interactions between fire and climate and make future predictions about carbon dynamics in these systems.Item Diurnal patterns of gas-exchange and metabolic pools in tundra plants during three phases of the arctic growing season(Wiley, 2013) Patankar, Rajit; Mortazavi, Behzad; Oberbauer, Steven F.; Starr, Gregory; University of Alabama Tuscaloosa; Dauphin Island Sea Lab; Florida International UniversityArctic tundra plant communities are subject to a short growing season that is the primary period in which carbon is sequestered for growth and survival. This period is often characterized by 24-h photoperiods for several months a year. To compensate for the short growing season tundra plants may extend their carbon uptake capacity on a diurnal basis, but whether this is true remains unknown. Here, we examined in situ diurnal patterns of physiological activity and foliar metabolites during the early, mid, and late growing season in seven arctic species under light-saturated conditions. We found clear diurnal patterns in photosynthesis and respiration, with midday peaks and midnight lulls indicative of circadian regulation. Diurnal patterns in foliar metabolite concentrations were less distinct between the species and across seasons, suggesting that metabolic pools are likely governed by proximate external factors. This understanding of diurnal physiology will also enhance the parameterization of process-based models, which will aid in better predicting future carbon dynamics for the tundra. This becomes even more critical considering the rapid changes that are occurring circumpolarly that are altering plant community structure, function, and ultimately regional and global carbon budgets.Item Ecosystem resistance in the face of climate change: a case study from the freshwater marshes of the Florida Everglades(Wiley, 2015-04-17) Malone, Sparkle L.; Keough, Cynthia; Staudhammer, Christina L.; Ryan, Michael G.; Parton, William J.; Olivas, Paulo; Oberbauer, Steven F.; Schedlbauer, Jessica; Starr, Gregory; University of Alabama Tuscaloosa; United States Department of Agriculture (USDA); United States Forest Service; Colorado State University; State University System of Florida; Florida International University; Pennsylvania State System of Higher Education (PASSHE); West Chester University of PennsylvaniaShaped by the hydrology of the Kissimmee-Okeechobee-Everglades watershed, the Florida Everglades is composed of a conglomerate of wetland ecosystems that have varying capacities to sequester and store carbon. Hydrology, which is a product of the region's precipitation and temperature patterns combined with water management policy, drives community composition and productivity. As shifts in both precipitation and air temperature are expected over the next 100 years as a consequence of climate change, CO2 dynamics in the greater Everglades are expected to change. To reduce uncertainties associated with climate change and to explore how projected changes in atmospheric CO2 concentration and climate can alter current CO2 exchange rates in Everglades freshwater marsh ecosystems, we simulated fluxes of carbon among the atmosphere, vegetation, and soil using the DAYCENT model. We explored the effects of low, moderate, and high scenarios for atmospheric CO2 (550, 850, and 950 ppm), mean annual air temperature (+1, +2.5, and +4.2 degrees C) and precipitation (-2, +7, and +14%), as predicted by the IPCC for the year 2100 for the region, on CO2 exchange rates in short- and long-hydroperiod wetland ecosystems. Under 100 years of current climate and atmospheric CO2 concentration, Everglades freshwater marsh ecosystems were estimated to be CO2-neutral. As atmospheric CO2 concentration increased and under climate change projections, there were slight shifts in the start and length of the wet season (-1 to +7 days) and a small enhancement in the sink capacity (by -169 to -573 g C m(-2) century(-1)) occurred at both short- and long-hydroperiod ecosystems compared to CO2 dynamics under the current climate regime. Over 100 years, rising temperatures increased net CO2 exchange rates (+1 to 13 g C m(-2) century(-1)) and shifts in precipitation patterns altered cumulative net carbon uptake by +13 to -46 g C m(-2) century(-1). While changes in ecosystem structure, species composition, and disturbance regimes were beyond the scope of this research, results do indicate that climate change will produce small changes in CO2 dynamics in Everglades freshwater marsh ecosystems and suggest that the hydrologic regime and oligotrophic conditions of Everglades freshwater marshes lowers the ecosystem sensitivity to climate change.Item Effects of drought and prescribed fire on energy exchange in longleaf pine ecosystems(Ecological Society of America, 2015-07-31) Whelan, Andrew; Starr, Gregory; Staudhammer, Christina L.; Loescher, Henry W.; Mitchell, Robert J.; University of Alabama Tuscaloosa; University of Colorado System; University of Colorado BoulderThe structure and function of longleaf pine savanna ecosystems is regulated by cyclic fire, yet there is a lack of understanding about how the frequency of fire influences longleaf pine ecosystem energy dynamics. There are further uncertainties in how predicted changes in temperature and precipitation may affect the interaction between fire and energy exchange in these ecosystems. We investigated energy dynamics in three frequently burned longleaf pine ecosystems along a gradient of soil moisture availability using eddy covariance techniques. We analyzed sensible energy (H), latent energy (LE) and soil heat flux (G) over time since fire, using micrometeorological variables as covariates. Based on statistical tests of autocorrelation, data were analyzed as 30-day averages with general linear models. Over three years of measurement, we found that sensible energy, latent energy and soil heat flux recovered to pre-fire rates within one month following prescribed fire. Changes in water availability associated with drought over the study period had a stronger influence on energy dynamics than did fire. When precipitation was near long-term averages, annual evapotranspiration (ET) was 743, 816 and 666 mm y(-1) at the mesic, intermediate and xeric sites, respectively. During extreme drought, annual ET decreased 4 and 7% at the xeric and intermediate sites, to 754 and 642 mm y(-1), respectively, and decreased 20% at the mesic site, to 594 mm y(-1). Similarly, Bowen ratios were up to two times higher during drought years versus those with average precipitation. These frequently burned longleaf pine ecosystems are known to be well adapted to fire. The more xeric the site, the more resilient they were to drought, suggesting adaptations of this ecosystem maintained higher levels of physiological activity. This three-year study begins to illuminate longleaf pine ecosystem energy dynamics, however long-term observations over a greater range of environmental conditions are necessary to increase our knowledge of the complex interactions between fire, climate and energy dynamics in these ecosystems.Item El Nino Southern Oscillation (ENSO) Enhances CO2 Exchange Rates in Freshwater Marsh Ecosystems in the Florida Everglades(PLOS, 2014-12-19) Malone, Sparkle L.; Staudhammer, Christina L.; Oberbauer, Steven F.; Olivas, Paulo; Ryan, Michael G.; Schedlbauer, Jessica L.; Loescher, Henry W.; Starr, Gregory; University of Alabama Tuscaloosa; United States Department of Agriculture (USDA); United States Forest Service; State University System of Florida; Florida International University; Colorado State University; Pennsylvania State System of Higher Education (PASSHE); West Chester University of Pennsylvania; University of Colorado System; University of Colorado BoulderThis research examines the relationships between El Nino Southern Oscillation (ENSO), water level, precipitation patterns and carbon dioxide (CO2) exchange rates in the freshwater wetland ecosystems of the Florida Everglades. Data was obtained over a 5-year study period (2009-2013) from two freshwater marsh sites located in Everglades National Park that differ in hydrology. At the short-hydroperiod site (Taylor Slough; TS) and the long-hydroperiod site (Shark River Slough; SRS) fluctuations in precipitation patterns occurred with changes in ENSO phase, suggesting that extreme ENSO phases alter Everglades hydrology which is known to have a substantial influence on ecosystem carbon dynamics. Variations in both ENSO phase and annual net CO2 exchange rates co-occurred with changes in wet and dry season length and intensity. Combined with site-specific seasonality in CO2 exchanges rates, El Nino and La Nina phases magnified season intensity and CO2 exchange rates at both sites. At TS, net CO2 uptake rates were higher in the dry season, whereas SRS had greater rates of carbon sequestration during the wet season. As La Nina phases were concurrent with drought years and extended dry seasons, TS became a greater sink for CO2 on an annual basis (-11 to -110 g CO2 m(-2) yr(-1)) compared to El Nino and neutral years (-5 to -43.5 g CO2 m(-2) yr(-1)). SRS was a small source for CO2 annually (1.81 to 80 g CO2 m(-2) yr(-1)) except in one exceptionally wet year that was associated with an El Nino phase (-16 g CO2 m(-2) yr(-1)). Considering that future climate predictions suggest a higher frequency and intensity in El Nino and La Nina phases, these results indicate that changes in extreme ENSO phases will significantly alter CO2 dynamics in the Florida Everglades.Item Fuel dynamics of a longleaf pine (pinus palustris mill.) woodland under a prescribed fire rotation(University of Alabama Libraries, 2020) Emery, Raien K.; Hart, Justin L.; University of Alabama TuscaloosaAs a result of historical logging and fire exclusion, longleaf pine (Pinus palustris Mill.) ecosystems have experienced extensive decline, now occurring on only 2–5% of its native range. Attempts to re-introduce fire into these forests where fuels have been altered by previous fire-exclusion or disturbance may not achieve desired management goals because fire effects are largely dependent on available fuels. To understand how fire impacts longleaf pine woodlands where fuels have been altered, fuel was collected before (2017) and after (2019) a prescribed fire on undisturbed, wind-disturbed, and wind-disturbed and salvage-harvested treatment types. In conjunction with percent consumption values calculated form laboratory burns, decomposition rates, and accumulation rates, fuel dynamics models were created and validated against post-fire fuel loadings. Total fuel loadings for undisturbed plots decreased 43%, wind-disturbed plots decreased 67%, and wind-disturbed and salvage-harvested plots decreased 53%. Fuel dynamics models successfully predicted post-fire fuel loadings for pine needles (rs = 0.782; p < 0.0001) and high flammability fuels (leaves, grass, bracken fern; rs = 0.529; p < 0.001) by plot, and further indicated that percent consumption values for other leafy fuels were accurate. I therefore concluded that laboratory burns can inform fire behavior in the field for leafy fuels. Forest structure models elucidated the varied effects of fire and time on the relationships between forest structures and fuel loading and composition. These models also showed stronger relationships between forest structures and leafy fuels (r2 = 0.655 to 0.811). Both models provide detailed depictions of how diverse longleaf pine woodland fuels change before and after a prescribed fire and may be used to accurately guide fuels management to achieve desired stand conditions.Item A general pattern of trade-offs between ecosystem resistance and resilience to tropical cyclones(American Association for the Advancement of Science, 2022) Patrick, Christopher J.; Kominoski, John S.; McDowell, William H.; Branoff, Benjamin; Lagomasino, David; Leon, Miguel; Hensel, Enie; Hensel, Marc J. S.; Strickland, Bradley A.; Aide, T. Mitchell; Armitage, Anna; Campos-Cerqueira, Marconi; Congdon, Victoria M.; Crowl, Todd A.; Devlin, Donna J.; Douglas, Sarah; Erisman, Brad E.; Feagin, Rusty A.; Geist, Simon J.; Hall, Nathan S.; Hardison, Amber K.; Heithaus, Michael R.; Hogan, J. Aaron; Hogan, J. Derek; Kinard, Sean; Kiszka, Jeremy J.; Lin, Teng-Chiu; Lu, Kaijun; Madden, Christopher J.; Montagna, Paul A.; O'Connell, Christine S.; Proffitt, C. Edward; Reese, Brandi Kiel; Reustle, Joseph W.; Robinson, Kelly L.; Rush, Scott A.; Santos, Rolando O.; Schnetzer, Astrid; Smee, Delbert L.; Smith, Rachel S.; Starr, Gregory; Stauffer, Beth A.; Walker, Lily M.; Weaver, Carolyn A.; Wetz, Michael S.; Whitman, Elizabeth R.; Wilson, Sara S.; Xue, Jianhong; Zou, Xiaoming; William & Mary; Virginia Institute of Marine Science; Florida International University; University of New Hampshire; University of Puerto Rico; University of Puerto Rico Rio Piedras; University of North Carolina; East Carolina University; University of Texas System; University of Texas Austin; Florida Fish & Wildlife Conservation Commission; Texas A&M University College Station; National Taiwan Normal University; South Florida Water Management District; Texas A&M University System; Macalester College; Dauphin Island Sea Lab; University of North Carolina Chapel Hill; University of Louisiana Lafayette; Mississippi State University; North Carolina State University; University of Virginia; University of Alabama Tuscaloosa; Millersville University of PennsylvaniaTropical cyclones drive coastal ecosystem dynamics, and their frequency, intensity, and spatial distribution are predicted to shift with climate change. Patterns of resistance and resilience were synthesized for 4138 ecosystem time series from n = 26 storms occurring between 1985 and 2018 in the Northern Hemisphere to predict how coastal ecosystems will respond to future disturbance regimes. Data were grouped by ecosystems (fresh water, salt water, terrestrial, and wetland) and response categories (biogeochemistry, hydrography, mobile biota, sedentary fauna, and vascular plants). We observed a repeated pattern of trade-offs between resistance and resilience across analyses. These patterns are likely the outcomes of evolutionary adaptation, they conform to disturbance theories, and they indicate that consistent rules may govern ecosystem susceptibility to tropical cyclones.Item How Do Urban Forests Compare? Tree Diversity in Urban and Periurban Forests of the Southeastern US(MDPI, 2016-06-09) Blood, Amy; Starr, Gregory; Escobedo, Francisco; Chappelka, Art; Staudhammer, Christina; University of Alabama Tuscaloosa; Universidad del Rosario; Auburn University System; Auburn UniversityThere is a need to understand how anthropogenic influences affect urban and periurban forest diversity at the regional scale. This study aims to compare urban and periurban tree composition along a geographic gradient, and test hypotheses about species composition and ecological homogeneity. We paired urban forest (UF) data from eight cities across the southeastern US with periurban forest (PF) data from the USDA Forest Service Forest Inventory and Analysis program. We found that tree diversity, as well as both observed and estimated species richness values were greater in UF versus PF. Community size structure analysis also indicated a greater proportion of large trees and greater numbers of non-native, invasive, and unclassified tree species in the UF versus the PF, regardless of location. Both forest type and ecological province had a significant effect on community species composition, with forests closer together in space being more similar to each other than those more distant. While land use change and management has been associated with ecological homogenization in human dominated landscapes, we found that species composition was more dissimilar along latitudinal lines than compared to between forest types, refuting this hypothesis, at least in terms of tree diversity.Item Large loss of CO2 in winter observed across the northern permafrost region(Nature Portfolio, 2019) Natali, Susan M.; Watts, Jennifer D.; Rogers, Brendan M.; Potter, Stefano; Ludwig, Sarah M.; Selbmann, Anne-Katrin; Sullivan, Patrick F.; Abbott, Benjamin W.; Arndt, Kyle A.; Birch, Leah; Bjorkman, Mats P.; Bloom, A. Anthony; Celis, Gerardo; Christensen, Torben R.; Christiansen, Casper T.; Commane, Roisin; Cooper, Elisabeth J.; Crill, Patrick; Czimczik, Claudia; Davydov, Sergey; Du, Jinyang; Egan, Jocelyn E.; Elberling, Bo; Euskirchen, Eugenie S.; Friborg, Thomas; Genet, Helene; Goeckede, Mathias; Goodrich, Jordan P.; Grogan, Paul; Helbig, Manuel; Jafarov, Elchin E.; Jastrow, Julie D.; Kalhori, Aram A. M.; Kim, Yongwon; Kimball, John S.; Kutzbach, Lars; Lara, Mark J.; Larsen, Klaus S.; Lee, Bang-Yong; Liu, Zhihua; Loranty, Michael M.; Lund, Magnus; Lupascu, Massimo; Madani, Nima; Malhotra, Avni; Matamala, Roser; McFarland, Jack; McGuire, A. David; Michelsen, Anders; Minions, Christina; Oechel, Walter C.; Olefeldt, David; Parmentier, Frans-Jan W.; Pirk, Norbert; Poulter, Ben; Quinton, William; Rezanezhad, Fereidoun; Risk, David; Sachs, Torsten; Schaefer, Kevin; Schmidt, Niels M.; Schuur, Edward A. G.; Semenchuk, Philipp R.; Shaver, Gaius; Sonnentag, Oliver; Starr, Gregory; Treat, Claire C.; Waldrop, Mark P.; Wang, Yihui; Welker, Jeffrey; Wille, Christian; Xu, Xiaofeng; Zhang, Zhen; Zhuang, Qianlai; Zona, Donatella; Woods Hole Research Center; University of Bayreuth; University of Alaska Anchorage; Brigham Young University; San Diego State University; University of Gothenburg; National Aeronautics & Space Administration (NASA); NASA Jet Propulsion Laboratory (JPL); California Institute of Technology; Northern Arizona University; Aarhus University; Norwegian Research Centre (NORCE); Columbia University; UiT The Arctic University of Tromso; Stockholm University; University of California Irvine; Pacific Geographical Institute of the Far Eastern Branch of the Russian Academy of Sciences; University of Montana; Dalhousie University; University of Copenhagen; University of Alaska Fairbanks; Max Planck Society; University of California San Diego; Scripps Institution of Oceanography; Queens University - Canada; McMaster University; Universite de Montreal; United States Department of Energy (DOE); Los Alamos National Laboratory; Argonne National Laboratory; University of Hamburg; University of Illinois Urbana-Champaign; Korea Polar Research Institute (KOPRI); Chinese Academy of Sciences; Shenyang Institute of Applied Ecology, CAS; Colgate University; National University of Singapore; Stanford University; United States Department of the Interior; United States Geological Survey; University of Exeter; University of Alberta; University of Oslo; Lund University; NASA Goddard Space Flight Center; Wilfrid Laurier University; University of Waterloo; Saint Francis Xavier University - Canada; Helmholtz Association; Helmholtz-Center Potsdam GFZ German Research Center for Geosciences; University of Colorado Boulder; University of Vienna; Marine Biological Laboratory - Woods Hole; University of Alabama Tuscaloosa; University of Eastern Finland; University of Oulu; University of Maryland College Park; Purdue University; Purdue University West Lafayette Campus; University of SheffieldRecent warming in the Arctic, which has been amplified during the winter(1-3), greatly enhances microbial decomposition of soil organic matter and subsequent release of carbon dioxide (CO2)(4). However, the amount of CO2 released in winter is not known and has not been well represented by ecosystem models or empirically based estimates(5,6). Here we synthesize regional in situ observations of CO2 flux from Arctic and boreal soils to assess current and future winter carbon losses from the northern permafrost domain. We estimate a contemporary loss of 1,662 TgC per year from the permafrost region during the winter season (October-April). This loss is greater than the average growing season carbon uptake for this region estimated from process models (-1,032 TgC per year). Extending model predictions to warmer conditions up to 2100 indicates that winter CO2 emissions will increase 17% under a moderate mitigation scenario-Representative Concentration Pathway 4.5-and 41% under business-as-usual emissions scenario-Representative Concentration Pathway 8.5. Our results provide a baseline for winter CO2 emissions from northern terrestrial regions and indicate that enhanced soil CO2 loss due to winter warming may offset growing season carbon uptake under future climatic conditions.Item Obtaining Improved Estimates of Soil Moisture, Evapotranspiration and its Components Using Physical Modeling and Big Data Analysis(University of Alabama Libraries, 2023) Raghav, Pushpendra; Kumar, MukeshThe Earth's climate-land-atmosphere (CLA) system is currently undergoing rapid and unprecedented transformations. These changes stem from a variety of factors, including the heightened release of greenhouse gases, widespread deforestation, rapid urbanization, expanding agriculture, and the alarming loss of wetlands. While significant progress has been made in predicting hydrologic states and fluxes within the CLA system, the accurate estimation of critical variables like root zone soil moisture (RZSM), evapotranspiration (ET), and its components, such as evaporation (E) and plant transpiration (T), remains a significant challenge. This dissertation utilizes physical models and data analytics to (i) elucidate the limitations of conventional methods for estimating RZSM, ET, its components, and plant evaporative stress, and (ii) introduce a novel approach to enhance RZSM estimates. The outcomes of this research establish the foundation for more reliable predictions of water and energy budgets, which will contribute to better-informed decisions regarding the management of water, forest, and food resources.Item A range-wide disturbance history for Quercus alba in the eastern US(University of Alabama Libraries, 2011) Buchanan, Megan Lindsay; Hart, Justin; University of Alabama TuscaloosaThroughout much of the eastern US, forests are undergoing a transition from Quercus to Acer-Fagus dominance. While the pattern has been reported in many site-specific analyses and is often linked to changes in disturbance regimes, a landscape-level analysis of historical establishment and disturbance throughout the region has not been conducted. I used tree-ring chronologies to analyze the disturbance history from old-growth Q. alba sites located throughout the species' range with the ultimate goal of determining the environmental conditions and disturbance dynamics that existed throughout the latter period of Quercus dominance and early period of Quercus decline. My analysis provided regional- and range-wide data regarding the frequency of disturbance throughout the development of old-growth Q. alba stands. In general, the temporal distribution of tree establishment dates was bimodal and corresponded to the period of Native American depopulation and the period following European settlement. Drought, Castanea dentata decline, and logging activities also significantly contributed to the long-term, range-wide disturbance regime. Regional discrepancies in release characteristics were identified. The Northern Hardwood Forest Region featured the highest level of disturbance as compared to all other regions. The Central Hardwood Forest Region exhibited the second lowest rate of disturbance (as evidenced by the relativized release descriptors). In general, high-magnitude disturbances occurred throughout the Q. alba range every 234-556 years. My findings confirm that Quercus dominance throughout the latter part of the Holocene was maintained, in part, by high magnitude disturbance events ca. every 400 years. Such high magnitude disturbances remove many disturbance-intolerant species, fragment large areas of the canopy, cause significant damage to subcanopy individuals, and allow disturbance-oriented and mid-successional taxa, such as Quercus, to establish. This return interval for high magnitude disturbance events can be imitated by land managers throughout the region in effort to promote Quercus regeneration.Item Seasonal patterns in energy partitioning of two freshwater marsh ecosystems in the Florida Everglades(American Geophysical Union, 2014-08-05) Malone, Sparkle L.; Staudhammer, Christina L.; Loescher, Henry W.; Olivas, Paulo; Oberbauer, Steven F.; Ryan, Michael G.; Schedlbauer, Jessica; Starr, Gregory; University of Alabama Tuscaloosa; United States Department of Agriculture (USDA); United States Forest Service; University of Colorado System; University of Colorado Boulder; State University System of Florida; Florida International University; Colorado State UniversityWe analyzed energy partitioning in short- and long-hydroperiod freshwater marsh ecosystems in the Florida Everglades by examining energy balance components (eddy covariance derived latent energy (LE) and sensible heat (H) flux). The study period included several wet and dry seasons and variable water levels, allowing us to gain better mechanistic information about the control of and changes in marsh hydroperiods. The annual length of inundation is similar to 5 months at the short-hydroperiod site (25 degrees 2616.5N, 80 degrees 3540.68W), whereas the long-hydroperiod site (25 degrees 336.72N, 80 degrees 4657.36W) is inundated for similar to 12 months annually due to differences in elevation and exposure to surface flow. In the Everglades, surface fluxes feed back to wet season precipitation and affect the magnitude of seasonal change in water levels through water loss as LE (evapotranspiration (ET)). At both sites, annual precipitation was higher than ET (1304 versus 1008 at the short-hydroperiod site and 1207 versus 1115 mm yr(-1) at the long-hydroperiod site), though there were seasonal differences in the ratio of ET:precipitation. Results also show that energy balance closure was within the range found at other wetland sites (60 to 80%) and was lower when sites were inundated (60 to 70%). Patterns in energy partitioning covaried with hydroperiods and climate, suggesting that shifts in any of these components could disrupt current water and biogeochemical cycles throughout the Everglades region. These results suggest that the complex relationships between hydroperiods, energy exchange, and climate are important for creating conditions sufficient to maintain Everglades ecosystems.