Browsing by Author "Loescher, Henry W."
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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 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 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.