Browsing by Author "Malone, Sparkle L."

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    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 Pennsylvania
    Shaped 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.
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    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 Boulder
    This 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.
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    Modeling Relationships among 217 Fires Using Remote Sensing of Burn Severity in Southern Pine Forests
    (MDPI, 2011-09-07) Malone, Sparkle L.; Kobziar, Leda N.; Staudhammer, Christina L.; Abd-Elrahman, Amr; State University System of Florida; University of Florida; University of Alabama Tuscaloosa
    Pine flatwoods forests in the southeastern US have experienced severe wildfires over the past few decades, often attributed to fuel load build-up. These forest communities are fire dependent and require regular burning for ecosystem maintenance and health. Although prescribed fire has been used to reduce wildfire risk and maintain ecosystem integrity, managers are still working to reintroduce fire to long unburned areas. Common perception holds that reintroduction of fire in long unburned forests will produce severe fire effects, resulting in a reluctance to prescribe fire without first using expensive mechanical fuels reduction techniques. To inform prioritization and timing of future fire use, we apply remote sensing analysis to examine the set of conditions most likely to result in high burn severity effects, in relation to vegetation, years since the previous fire, and historical fire frequency. We analyze Landsat imagery-based differenced Normalized Burn Ratios (dNBR) to model the relationships between previous and future burn severity to better predict areas of potential high severity. Our results show that remote sensing techniques are useful for modeling the relationship between elevated risk of high burn severity and the amount of time between fires, the type of fire (wildfire or prescribed burn), and the historical frequency of fires in pine flatwoods forests.
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    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 University
    We 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.