DSpace Repository :: Browsing by Author "Staudhammer, Christina L."

Browsing by Author "Staudhammer, Christina L."

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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 Boulder
Drought 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.
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 Madison
Understanding 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.
Comparative models disentangle drivers of fruit production variability of an economically and ecologically important long-lived Amazonian tree
(Nature Portfolio, 2021) Staudhammer, Christina L.; Wadt, Lucia Helena O.; Kainer, Karen A.; da Cunha, Thiago Augusto; University of Alabama Tuscaloosa; Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA); University of Florida; Universidade Federal do Acre (UFAC)
Trees in the upper canopy contribute disproportionately to forest ecosystem productivity. The large, canopy-emergent Bertholletia excelsa also supports a multimillion-dollar commodity crop (Brazil nut), harvested almost exclusively from Amazonian forests. B. excelsa fruit production, however is extremely variable within populations and years, destabilizing local harvester livelihoods and the extractive economy. To understand this variability, data were collected in Acre, Brazil over 10 years at two sites with similar climate and forest types, but different fruit production levels, despite their proximity (similar to 30 km). One site consistently produced more fruit, showed less individual- and population-level variability, and had significantly higher soil P and K levels. The strongest predictor of fruit production was crown area. Elevation and sapwood area also significantly impacted fruit production, but effects differed by site. While number of wet days and dry season vapor pressure prior to flowering were significant production predictors, no climatic variables completely captured annual observed variation. Trees on the site with higher available P and K produced nearly three times more fruits, and appeared more resilient to prolonged drought and drier atmospheric conditions. Management activities, such as targeted fertilization, may shield income-dependent harvesters from expected climate changes and production swings, ultimately contributing to conservation of old growth forests where this species thrives.
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.
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 Boulder
The 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.
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.
The importance of multimodel projections to assess uncertainty in projections from simulation models
(Wiley, 2019-01-10) Valle, Denis; Staudhammer, Christina L.; Cropper, Wendell P., Jr.; van Gardingen, Paul R.; State University System of Florida; University of Florida; Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA); University of Edinburgh; University of Alabama Tuscaloosa
Simulation models are increasingly used to gain insights regarding the long-term effect of both direct and indirect anthropogenic impacts on natural resources and to devise and evaluate policies that aim to minimize these effects. If the uncertainty from simulation model projections is not adequately quantified and reported, modeling results might be misleading, with potentially serious implications. A method is described, based on a nested simulation design associated with multimodel projections, that allows the partitioning of the overall uncertainty in model projections into a number of different sources of uncertainty: model stochasticity, starting conditions, parameter uncertainty, and uncertainty that originates from the use of key model assumptions. These sources of uncertainty are likely to be present in most simulation models. Using the forest dynamics model SYMFOR as a case study, it is shown that the uncertainty originated from the use of alternate modeling assumptions, a source of uncertainty seldom reported, can be the greatest source of uncertainty, accounting for 66-97% of the overall variance of the mean after 100 years of stand dynamics simulation. This implicitly reveals the great importance of these multimodel projections even when multiple models from independent research groups are not available. Finally, it is suggested that a weighted multimodel average (in which the weights are estimated from the data) might be substantially more precise than a simple multimodel average (equivalent to equal weights for all models) as models that strongly conflict with the data are given greatly reduced or even zero weights. The method of partitioning modeling uncertainty is likely to be useful for other simulation models, allowing for a better estimate of the uncertainty of model projections and allowing researchers to identify which data need to be collected to reduce this uncertainty.
Integrating field and remote sensing analyses of aboveground biomass dynamics during secondary forest regeneration in Costa Rica
(University of Alabama Libraries, 2017) Davis, Kelsi Lyn; Senkbeil, Jason C.; University of Alabama Tuscaloosa
The process tropical aboveground biomass (AGB) plays in the global carbon cycle is imperative to preserve in the efforts to combat the effects of climate change through climate mitigation strategies. However, there is currently an insufficient understanding of AGB distribution and dynamics in tropical forests, and a lack of time and cost-effective means of estimating AGB. Species identification, location, diameter-at-breast-height (DBH), and AGB were determined at the stem-level in four 0.5 ha plots in a Costa Rican tropical wet forest to assess the distributional patterns of AGB, and its partitioning among various forest stand ages. Remotely-sensed data of the plots was collected utilizing a PrecisionHawk Rev4 unmanned aerial system (UAS) equipped with a dual-return light detection and ranging (LiDAR) sensor to calibrate with field data to determine if it could accurately estimate AGB in a densely forested environment. Species richness varied among forest stand ages, and had a slight negative impact on AGB at a fine spatial scale. Tree stems 5 – 24 cm in DBH represent over 80% of all stems included in the AGB analyses, yet contribute less than half of the total AGB represented among the plots. Vegetation distribution and characteristics of biomass clustering evolved with forest stand age. Height metrics were extracted from a LiDAR-derived digital elevation model (DEM) and digital surface model (DSM), and predictive calibration models were generated to estimate AGB from the remotely-sensed data. However, extracting height metrics from the LiDAR data emphasized the challenges associated with accurate spatial modeling of a dense tropical forest.
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.
Population Structure and Fruit Production of Carapa guianensis (Andiroba) in Amazonian Floodplain Forests: Implications for Community-Based Management
(Sage, 2017) Londres, Marina; Schulze, Mark; Staudhammer, Christina L.; Kainer, Karen A.; State University System of Florida; University of Florida; Oregon State University; University of Alabama Tuscaloosa
Andiroba (Carapa guianensis) is a multiple-use tree species that plays a crucial socioeconomic role across thousands of Amazonian traditional and indigenous communities. In the floodplain forests of the Amazon estuary, we partnered with local forest managers to investigate C. guianensis ecological parameters, addressing seed production rates, tree density, and size class structure across a range of environmental conditions and forest use history. C. guianensis population structure was measured in three forest types: baixio, restinga, and terra preta, differentiated by tidal influence, species dominance and composition, and edaphic conditions. We found significant differences across forest types, whereby seedling and sapling densities were higher in terra preta and adult densities were higher in baixio. Adult densities were 28.7, 23.0, and 19.5 trees/ha, and seedling densities were 22.9, 105, and 151 trees/ha in baixio, restinga, and terra preta forest types, respectively. Seed production rates varied significantly across forest types, year, size class, crown form, and crown illumination. There were higher numbers of viable seeds in terra preta versus baixio (5.5 kg and 2.6 seeds/tree/year, respectively) as well as more trees with better crown forms, more light, and larger diameter sizes. Long-term patterns of community timber management intensity by forest type significantly influenced both population structure and population-level seed production. Nonetheless, assessment of seed production for the total population suggests that the local community was collecting less than 1% of the viable C. guianensis seeds produced annually within community forest lands. This study illustrates the potential of management to impact the sustainability of an important multiple use species and shows the impact that community conservation planning and action can have on future natural resource availability.
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.
Towards an empirical relationship between root length density and root number in windbreak-grown cadaghi (Corymbia torelliana) trees
(2011-11-30) Tamang, Bijay; Andreu, Michael G.; Staudhammer, Christina L.; Rockwood, Donald L.; Jose, Shibu; University of Alabama Tuscaloosa
Because windbreaks are planted for sustainable agriculture but may lower crop yields near them due to competition, suitable competition mitigation methods must be applied at the windbreak-crop interface to increase crop yields. Effective underground competition management requires information on important root variables such as preferential root growth direction and root length density (RLD, root length per unit volume of soil). This study examined root isotropy (i.e., uniformity in all directions) in windbreak- grown cadaghi (Corymbia torelliana) trees in south Florida and developed an empirical relationship between RLD and number of roots (N) per unit of surface of soil exiting the trench face. Numbers of roots exiting the frontal face parallel to the windbreak (NX), vertical face perpendicular to the frontal face (NY), and basal horizontal face (NZ) of 10 x 10 x 10 cm soil cubes were counted. Cadaghi roots were anisotropic and had horizontal growth preference. Average root numbers were ranked NX>NY>NZ. Both NX and the average root number exiting X, Y and Z faces of the soil cube (NAVG) were significant variables for estimating RLD. The coefficients of NX and NAVG were 1.1 and 3.1. These results should be helpful to manage underground competition effectively at the windbreak-crop interface to improve crop yields.

Browsing by Author "Staudhammer, Christina L."

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