Search

Wetlands are the largest natural source of methane (CH4); however, the contribution of subtropical wetlands to global CH4 budgets is still unclear due to difficulties in accurately quantifying CH4 emissions from these complex ecosystems. Both direct (water management strategies) and indirect (altered weather patterns associated with climate change) anthropogenic influences are also leading to greater uncertainties in our ability to determine changes in CH4 emissions from these ecosystems. This study compares CH4 fluxes from two freshwater marshes with different hydroperiods (short versus long) in the Florida Everglades to examine temporal patterns and biophysical drivers of CH4 fluxes. Both sites showed similar seasonal patterns across years with higher CH4 release during wet seasons versus dry seasons. The long hydroperiod site showed stronger seasonal patterns and overall, emitted more CH4 than the short hydroperiod site; however, no distinctive diurnal patterns were observed. We found that air temperature was a significant positive driver of CH4 fluxes for both sites regardless of season. In addition, gross ecosystem exchange was a significant negative predictor of CH4 emissions in the dry season at the long hydroperiod site. CH4 fluxes were impacted by water level and its changes over site and season, and time scales, which are influenced by rainfall and water management practices. Thus with increasing water distribution associated the Comprehensive Everglades Restoration Plan we expect increases in CH4 emissions, and when couple with increased with projected higher temperatures in the region, these increases may be enhanced, leading to greater radiative forcing. [ABSTRACT FROM AUTHOR]

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 (~ 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. [ABSTRACT FROM AUTHOR]

Amphibian life history traits are affected by temperature and precipitation. Yet, connecting these relationships to population growth, especially for multiple populations within a species, is lacking and precludes our understanding of amphibian population dynamics and distributions. Therefore, we constructed integral projection models for five populations along an elevational gradient to determine how climate and season affect population growth of a terrestrial salamander Plethodon montanus and the importance of demographic vital rates to population growth under varying climate scenarios. We found that population growth was typically higher at the highest elevation compared to the lower elevations, whereas varying inactive season conditions, represented by the late fall, winter and early spring, produced a greater variation in population growth than varying active season conditions (late spring, summer, and early fall). Furthermore, survival and growth were consistently more important, as measured by elasticity, compared to fecundity, and large females had the greatest elasticity compared to all other body sizes. Our results suggest that changing inactive season conditions, especially those that would affect the survival of large individuals, may have the greatest impact on population growth. We recommend future experimental studies focus on the inactive season to better elucidate the mechanisms by which these conditions can affect survival. [ABSTRACT FROM AUTHOR]

In sum, the more sapwood, the more likely any individual tree could continue producing fruits even in the face of a drier atmosphere." now reads: "Model 2 revealed that higher VAP levels (more moist air) limited fruit production, but this was mitigated when trees had more sapwood area, particularly in Cachoeira (Fig. "Model 2 revealed that higher VAP levels (drier air) limited fruit production, but this was mitigated when trees had more sapwood area, particularly in Cachoeira (Fig. [Extracted from the article]

Globally, soil CO2 efflux rates (Fs) have been linked to changes in soil water content (SWC), rainfall and temperature and/or productivity. However, within an ecosystem, Fs can vary based on site structure and function, which can be affected by a combination of abiotic and biotic factors. This becomes particularly important when an ecosystem is faced with disturbances, such as drought or fire. Site-specific compensatory responses to disturbances may therefore alter C mineralization, as well as root respiration. Hence, single location Fs estimates may not be a representative for ecosystems across their distributional ranges. We conducted a 6-year study along an edaphic moisture gradient of longleaf pine ecosystems that were maintained with prescribed fire, using eddy covariance and soil respiration measurements to address how Fs varies with changes in ecosystem structure and function, as well as disturbances. Lower air temperatures (Tair) decreased Fs at all sites, but that response was also affected by productivity and SWC. Productivity significantly altered Fs rates at all sites, especially when we accounted for changes in temperature and SWC. Plant regrowth post-fire temporarily increased Fs (10-40%), whereas drought reduced Fs at all sites. Our results show that site productivity, Fs and the degree to which ecosystems adapt to climate variations and disturbance can be site specific. Hence, model forecasting of carbon dynamics would strongly benefit from multi-location measurements of Fs across the distributional range of an ecosystem. [ABSTRACT FROM AUTHOR]

We examined the spatial distribution, occurrence, and socioecological predictors of woody invasive plants (WIP) in two subtropical, coastal urban ecosystems: San Juan, Puerto Rico and Miami-Dade, United States. These two cities have similar climates and ecosystems typical of subtropical regions but differ in socioeconomics, topography, and urbanization processes. Using permanent plot data, available forest inventory protocols and statistical analyses of geographic and socioeconomic spatial predictors, we found that landscape level distribution and occurrence of WIPs was not clustered. We also characterized WIP composition and occurrence using logistic models, and found they were strongly related to the proportional area of residential land uses. However, the magnitude and trend of increase depended on median household income and grass cover. In San Juan, WIP occurrence was higher in areas of high residential cover when incomes were low or grass cover was low, whereas the opposite was true in Miami-Dade. Although Miami-Dade had greater invasive shrub cover and numbers of WIP species, San Juan had far greater invasive tree density, basal area and crown cover. This study provides an approach for incorporating field and available census data in geospatial distribution models of WIPs in cities throughout the globe. Findings indicate that identifying spatial predictors of WIPs depends on site-specific factors and the ecological scale of the predictor. Thus, mapping protocols and policies to eradicate urban WIPs should target indicators of a relevant scale specific to the area of interest for their improved and proactive management. [ABSTRACT FROM AUTHOR]

This research examines the relationships between El Niño 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 Niño and La Niña 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 Niña 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 Niño 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 Niño phase (−16 g CO2 m−2 yr−1). Considering that future climate predictions suggest a higher frequency and intensity in El Niño and La Niña phases, these results indicate that changes in extreme ENSO phases will significantly alter CO2 dynamics in the Florida Everglades. [ABSTRACT FROM AUTHOR]

In aquatic environments around the globe, rooted macrophytes have been replaced by filamentous macroalgae. The consequences of such shifts in vegetative habitat for fauna are poorly understood. Given differences in morphology and life history characteristics of rooted macrophytes and filamentous macroalgae, we hypothesized that these habitat types were not functionally redundant for small-bodied fishes and macroinvertebrates. We examined this hypothesis in spring-fed Florida rivers characterized by decreases in native rooted macrophytes and concomitant increases in filamentous macroalgae. Although faunal densities were generally greater in filamentous macroalgae than in rooted macrophytes, differences in the community assemblage structure suggest that the two types of vegetative habitat do not function interchangeably. Accordingly, continued replacement of rooted macrophytes with filamentous macroalgae is expected to affect the small fish and macroinvertebrate community, as well as higher trophic levels that depend on it. [ABSTRACT FROM AUTHOR]

Few studies within the native range of loblolly (Pinus taeda L.) and slash pine (Pinus elliottii Engelm. var. elliottii) have compared yield and stand dynamics in pure-family block versus mixed-family block plantings under a range of silvicultural treatments. Understanding intergenotypic competitive interactions is important for predicting phenotypic performance, defining growth strategies and ideotypes, and deploying the correct mix of families that possess complementary characteristics for enhanced yield and pest resistance. In 2000, replicated experimental trials were installed in the southeastern United States, controlling for genotype (pure- and mixed-family plantings; consisting of seven full-sibling loblolly and six full-sibling slash pine families), planting density (1334 vs. 2990 trees/ha), [ABSTRACT FROM AUTHOR]

Premise: Wetland plants regularly experience physiological stresses resulting from inundation; however, plant responses to the interacting effects of water level and inundation duration are not fully understood. Methods: We conducted a mesocosm experiment on two wetland species, sawgrass (Cladium jamaicense) and muhly grass (Muhlenbergia filipes), that co‐dominate many freshwater wetlands in the Florida Everglades. We tracked photosynthesis, respiration, and growth at water levels of −10 (control), 10 (shallow), and 35 cm (deep) with reference to soil surface over 6 months. Results: The response of photosynthesis to inundation was nonlinear. Specifically, photosynthetic capacity (Amax) declined by 25% in sawgrass and by 70% in muhly grass after 1–2 months of inundation. After 4 months, Amax of muhly grass in the deep‐water treatment declined to near zero. Inundated sawgrass maintained similar leaf respiration and growth rates as the control, whereas inundated muhly grass suppressed both respiration and growth. At the end of the experiment, sawgrass had similar nonstructural carbohydrate pools in all treatments. By contrast, muhly grass in the deep‐water treatment had largely depleted sugar reserves but maintained a similar starch pool as the control, which is critical for post‐stress recovery. Conclusions: Overall, the two species exhibited nonlinear and contrasting patterns of carbon uptake and use under inundation stress, which ultimately defines their strategies of surviving regularly flooded habitats. The results suggest that a future scenario with more intensive inundation, due to the water management and climate change, may weaken the dominance of muhly grass in many freshwater wetlands of the Everglades. [ABSTRACT FROM AUTHOR]

Non-timber forest product ( NTFP) harvest is frequently accompanied by resource management practices that interact with the harvesting itself, other disturbances and abiotic conditions. These interactions, in turn, lead to diverse environmental effects. Few studies focus on these practices in the context of harvesting NTFPs, product properties and environmental impacts, including biological invasions., In Pine woodlands in Eastern Bhutan, Cymbopogon flexuosus East Indian Lemon Grass is harvested and distilled to obtain essential oil, an economically important NTFP. Prescribed fires are applied in late winter (before annual harvest in summer) to induce regeneration of new tillers with increased essential oil content. This practice is based on local ecological knowledge and renders the utilization of C. flexuosus economically viable. On two sites with contrasting stand structure, we evaluated the effects of different prescribed burning regimes (no burning vs. burning with two levels of frequency and intensity) on the sustainability of annually harvested C. flexuosus, regarding cover, biomass yield, essential oil yield and quality. At the same time, we evaluated the effects of prescribed burning on the spread of the invasive shrub Chromolaena odorata., Cymbopogon flexuosus biomass declined over time, likely as a result of harvesting. In more closed stands, it was moreover marginally negatively influenced by fire. We confirmed local ecological knowledge regarding significantly higher essential oil yield on burned plots, without differences between fire regimes., In open stands, fire led to rapid expansion of C. odorata, specifically with frequently applied, higher intensity fires. Additionally, the spread of C. odorata showed adverse effects on C. flexuosus cover., Synthesis and applications. Our results highlight the importance of studying the wider impacts of non-timber forest product ( NTFP) harvest. We confirmed local ecological knowledge that fire increases lemon grass essential oil yield, making prescribed burning an attractive land management tool for farmers. Nevertheless, the practice of annual harvesting may lead to resource decline that may be exacerbated by fire in closed stands. Caution needs to be practiced on open sites where invasive C. odorata may spread rapidly after fires. Management needs to focus on preventing concentration of annual harvesting and associated prescribed burning in the same areas. Amending national forestry rules to legalize fire as a land management tool can support local economies and potentially prevent wildfires that regularly devastate human infrastructure across eastern Bhutan. [ABSTRACT FROM AUTHOR]

How aquatic primary productivity influences the carbon (C) sequestering capacity of wetlands is uncertain. We evaluated the magnitude and variability in aquatic C dynamics and compared them to net ecosystem CO2 exchange (NEE) and ecosystem respiration (Reco) rates within calcareous freshwater wetlands in Everglades National Park. We continuously recorded 30-min measurements of dissolved oxygen (DO), water level, water temperature (Twater), and photosynthetically active radiation (PAR). These measurements were coupled with ecosystem CO2 fluxes over 5 years (2012–2016) in a long-hydroperiod peat-rich, freshwater marsh and a short-hydroperiod, freshwater marl prairie. Daily net aquatic primary productivity (NAPP) rates indicated both wetlands were generally net heterotrophic. Gross aquatic primary productivity (GAPP) ranged from 0 to − 6.3 g C m−2 day−1 and aquatic respiration (RAq) from 0 to 6.13 g C m−2 day−1. Nonlinear interactions between water level, Twater, and GAPP and RAq resulted in high variability in NAPP that contributed to NEE. Net aquatic primary productivity accounted for 4–5% of the deviance explained in NEE rates. With respect to the flux magnitude, daily NAPP was a greater proportion of daily NEE at the long-hydroperiod site (mean = 95%) compared to the short-hydroperiod site (mean = 64%). Although we have confirmed the significant contribution of NAPP to NEE in both long- and short-hydroperiod freshwater wetlands, the decoupling of the aquatic and ecosystem fluxes could largely depend on emergent vegetation, the carbonate cycle, and the lateral C flux. [ABSTRACT FROM AUTHOR]

Lianas or woody vines can be detrimental to the trees that support them. Research on liana cutting for tropical timber management has demonstrated positive yet costly benefits, but liana cutting to enhance commercial outputs of nontimber forest products has not been examined. We implemented a controlled experiment to quantify the effects of cutting lianas on Brazil nut Bertholletia excelsa Bonpl. fecundity., We conducted our 10-year experiment in a Brazilian extractive reserve where local harvesters collect fruits from this Amazonian canopy-emergent species as part of their forest-based livelihood system. We cut 454 lianas with a total basal area of 2·41 m2 from 78 of 138 host trees ≥50 cm diameter at breast height., Treated trees were significantly better producers 3 ½ years after liana cutting, and these differences increased dramatically in subsequent years, with consistent proportionally higher production in treated versus untreated individuals., The number of lianas rooted within 5 m of the host tree significantly explained production levels, suggesting both above- and below-ground liana-host tree competition. Once host crowns were liana-free, branch regrowth was highly visible, particularly in heavily infested trees, and crown reassessments suggested that liana cutting improved crown form. Additionally, liana cutting may induce some nonproducing trees to become producers and may circumvent mortality of trees heavily infested with lianas (> 75% crown covered)., Liana removal can be implemented easily when harvesting Brazil nut fruits. Only lianas associated with B. excelsa trees should be cut to conserve liana ecosystem functions., Synthesis and applications. We quantified effects of liana cutting on Brazil nut host tree fecundity and provided estimates of increased commercial yields. Our long-term (10-year) study permits understanding of biological variation and informs related management decisions. Findings suggest that liana cutting reduces above- and below-ground competition with individual trees, ultimately allowing mature host crowns to recover such that 9-10 years after liana cutting, treated trees produced on average three times more fruits than untreated trees. Application of liana cutting to other tropical species would likely boost fruit and seed production, increase host tree fecundity and potentially enhance future recruitment. [ABSTRACT FROM AUTHOR]

Hydrology drives the carbon balance of wetlands by controlling the uptake and release of CO2 and CH4. Longer dry periods in between heavier precipitation events predicted for the Everglades region, may alter the stability of large carbon pools in this wetland's ecosystems. To determine the effects of drought on CO2 fluxes and CH4 emissions, we simulated changes in hydroperiod with three scenarios that differed in the onset rate of drought (gradual, intermediate, and rapid transition into drought) on 18 freshwater wetland monoliths collected from an Everglades short-hydroperiod marsh. Simulated drought, regardless of the onset rate, resulted in higher net CO2 losses net ecosystem exchange ( NEE) over the 22-week manipulation. Drought caused extensive vegetation dieback, increased ecosystem respiration ( Reco), and reduced carbon uptake gross ecosystem exchange ( GEE). Photosynthetic potential measured by reflective indices (photochemical reflectance index, water index, normalized phaeophytinization index, and the normalized difference vegetation index) indicated that water stress limited GEE and inhibited Reco. As a result of drought-induced dieback, NEE did not offset methane production during periods of inundation. The average ratio of net CH4 to NEE over the study period was 0.06, surpassing the 100-year greenhouse warming compensation point for CH4 (0.04). Drought-induced diebacks of sawgrass (C3) led to the establishment of the invasive species torpedograss (C4) when water was resupplied. These changes in the structure and function indicate that freshwater marsh ecosystems can become a net source of CO2 and CH4 to the atmosphere, even following an extended drought. Future changes in precipitation patterns and drought occurrence/duration can change the carbon storage capacity of freshwater marshes from sinks to sources of carbon to the atmosphere. Therefore, climate change will impact the carbon storage capacity of freshwater marshes by influencing water availability and the potential for positive feedbacks on radiative forcing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Climate change has altered global precipitation patterns and has led to greater variation in hydrological conditions. Wetlands are important globally for their soil carbon storage. Given that wetland carbon processes are primarily driven by hydrology, a comprehensive understanding of the effect of inundation is needed. In this study, we evaluated the effect of water level (WL) and inundation duration (ID) on carbon dioxide (CO2) fluxes by analysing a 10‐year (2008–2017) eddy covariance dataset from a seasonally inundated freshwater marl prairie in the Everglades National Park. Both gross primary production (GPP) and ecosystem respiration (ER) rates showed declines under inundation. While GPP rates decreased almost linearly as WL and ID increased, ER rates were less responsive to WL increase beyond 30 cm and extended inundation periods. The unequal responses between GPP and ER caused a weaker net ecosystem CO2 sink strength as inundation intensity increased. Eventually, the ecosystem tended to become a net CO2 source on a daily basis when either WL exceeded 46 cm or inundation lasted longer than 7 months. Particularly, with an extended period of high‐WLs in 2016 (i.e., WL remained >40 cm for >9 months), the ecosystem became a CO2 source, as opposed to being a sink or neutral for CO2 in other years. Furthermore, the extreme inundation in 2016 was followed by a 4‐month postinundation period with lower net ecosystem CO2 uptake compared to other years. Given that inundation plays a key role in controlling ecosystem CO2 balance, we suggest that a future with more intensive inundation caused by climate change or water management activities can weaken the CO2 sink strength of the Everglades freshwater marl prairies and similar wetlands globally, creating a positive feedback to climate change. [ABSTRACT FROM AUTHOR]

The eddy covariance (EC) technique has been widely used to measure ecosystem surface energy fluxes. However, with a relatively small representative area (footprint), errors are often introduced when upscaling EC data based on variables derived from large-footprint satellite products. Furthermore, EC measurements often fail to close the energy balance in ecosystems such as wetlands. As an alternative to EC, large aperture scintillometers (LAS) have been used to measure sensible heat fluxes (H) over representative areas comparable to the resolution of large-scale satellite images. However, because LAS measurements are based on semi-empirical simulations, their accuracy needs further evaluation across ecosystems. Changes in hydrology on the land surface significantly alter measurement conditions as well as the processes of energy transfer, and thus, may affect the accuracy of energy measurements from LAS. To address this issue, we compared the LAS-measured H (H LAS ) to EC-derived H (H EC ) in a seasonally inundated wetland within Everglades National Park. Overall, the H LAS was 7.1 ± 0.3 (SE) % greater than H EC , and the ratio of H LAS to H EC remained similar between the wet season, when the ecosystem was inundated, and the dry season. However, inundation, as a thermal buffer in the system, reduced the magnitude of H in the wet season and resulted in a smaller difference of seasonal H budget estimates between LAS and EC measurements. Because of the homogenous land surface at our site, the discrepancies between H LAS and H EC could not be explained by footprint mismatch. Compared to the energy balance closure calculated with H EC , the closure calculated with H LAS was improved by 6% during the dry season but remained similar during the wet season. Overall, we conclude that LAS can be a reliable approach to measure H in wetland ecosystems and its measurements were stable with seasonal hydrological changes. [ABSTRACT FROM AUTHOR]

The high utility of eddy covariance (EC) data has made it the cornerstone of carbon dynamics research for more than two decades. However, a substantial number of measurements from EC data can be missing for various reasons. Robust gap-filling methods are required to estimate carbon budgets from net ecosystem exchange measurements of CO 2 (NEE) with high precision and accuracy. While the gap-filled methods used have provided unbiased estimates of annual NEE, little research has been done on preserving the variance structures associated with gap-filled flux data. In this project, we used EC data from a longleaf pine ecosystem located in the southeast US to investigate variance preservation in gap-filling methods. We used three non-linear regression approaches to impute artificially created gaps of different sizes via light and temperature response curves: 1) “traditional” fixed monthly window, 2) moving window, and 3) moving window with parameter prediction using physiological drivers. The results of gap-filling simulations showed that the variability of NEE estimates made with moving window and parameter prediction methods were closer to that of observed NEE, whereas the traditional method had overall lower variability. The average root mean square errors (RMSE) of predictions was lower for moving window and parameter prediction (3.38 and 3.22, respectively), versus that of the traditional method (3.42) over one year, including both daytime and nighttime data across all gap sizes. The variances associated with moving window and parameter prediction methods were 52% and 57%, respectively, of the observed variance, versus that of the traditional (51%), while the average of first-order autocorrelation coefficients was 0.76 for each method compared to 0.58 for observed. The results showed that the moving window approaches provided better estimates (lower RMSEs and more similar variance) at annual scales, yet underestimated the observed variance. These results contribute toward the development of a framework of standardized gap-filling approaches which maintain variation inherent in EC data. Moreover, these results call for further research on potential environmental drivers and their interactions for inclusion in gap-filling models, as well as exploration of sampling size of estimation windows and averaging time (half hour) of flux data to promote variance maintenance and decrease the autocorrelation of predictions. [ABSTRACT FROM AUTHOR]

To quantify the effect of oysters on sediment N cycling, oyster-free cages and cages with adult or juvenile oysters [Crassostrea virginica (Gmelin, 1791)] were suspended above the sediments at two sites in Mobile Bay, Alabama, located in the northern Gulf of Mexico. While hydrogen sulfide (HS-) was below detection limits at Site 2, HS- exceeded 500 μM prior to the deployment at Site 1 and remained detectable in sediments in the oyster treatments. Oyster mediated N inputs were estimated at 11.4 (SE 0.4) g N m-2 and 3.2 (SE 0.2) g N m-2 in the juvenile and adult treatments, respectively. The abundances of genes associated with denitrifiers (nirK), sulfate reducers (dsrB), and bacterial and archaeal nitrifiers (bac_amoA, arc_amoA, respectively) varied over the course of the study, but were not affected by the treatments. Similarly, potential denitrification rates measured during the study were similar in all treatments. Net N2 fluxes, determined from N2: Ar ratios using a membrane inlet mass spectrometer were similar among treatments, despite significantly higher sediment chlorophyll-a content in the juvenile treatment. We conclude that the commonly assumed enhanced rates of N2 loss from sediments in response to deployment of oysters is not guaranteed and may depend on site-specific biogeochemistry. [ABSTRACT FROM AUTHOR]

Forests are experiencing simultaneous changes in climate, disturbance regimes, and management, all of which affect ecosystem function. Climate change is shifting ranges and altering forest productivity. Disturbance regimes are changing with the potential for novel interactions among disturbance types. In some areas, forest management practices are intensifying, whereas in other areas, lower-impact ecological methods are being used. Interactions among these changing factors are likely to alter ecosystem structure and function at regional to continental scales. A macrosystems approach is essential to assessing the broadscale impacts of these changes and quantify cross-scale interactions, emergent patterns, and feedbacks. A promising line of analysis is the assimilation of data with ecosystem models to scale processes to the macrosystem and generate projections based on alternative scenarios. Analyses of these projections can characterize the range of future variability in forest function and provide information to guide policy, industry, and science in a changing world. [ABSTRACT FROM PUBLISHER]

One of the most important changes in high-latitude ecosystems in response to climatic warming may be the thawing of permafrost soil. In upland tundra, the thawing of ice-rich permafrost can create localized surface subsidence called thermokarst, which may change the soil environment and influence ecosystem carbon release and uptake. We established an intermediate scale (a scale in between point chamber measurements and eddy covariance footprint) ecosystem carbon flux study in Alaskan tundra where permafrost thaw and thermokarst development had been occurring for several decades. The main goal of our study was to examine how dynamic ecosystem carbon fluxes [gross primary production (GPP), ecosystem respiration ( R), and net ecosystem exchange (NEE)] relate to ecosystem variables that incorporate the structural and edaphic changes that co-occur with permafrost thaw and thermokarst development. We then examined how these measured ecosystem carbon fluxes responded to upscaling. For both spatially extensive measurements made intermittently during the peak growing season and intensive measurements made over the entire growing season, ecosystem variables including degree of surface subsidence, thaw depth, and aboveground biomass were selected in a mixed model selection procedure as the 'best' predictors of GPP, R, and NEE. Variables left out of the model (often as a result of autocorrelation) included soil temperature, moisture, and normalized difference vegetation index. These results suggest that the structural changes (surface subsidence, thaw depth, aboveground biomass) that integrate multiple effects of permafrost thaw can be useful components of models used to estimate ecosystem carbon exchange across thermokarst affected landscapes. [ABSTRACT FROM AUTHOR]

• Thermodynamics were used quantify ecosystem responses to extreme temperatures. • Longleaf pine energy reserves are built during low precipitation and mild temperatures. • Human modification to an ecosystem slows their metabolic recovery. • Modification of the natural environment can reduce the "memory" of the ecosystem. The southeastern US has experienced an increase in the number of extreme heat events since the 1970s, due in part to global change. Despite rising temperatures, greater variability in weather has also led to more freeze events across parts of the Southeast, particularly during El Niño winters. Structural variation in forest stands and plant functional diversity can lead to localized micrometeorological differences that may alter the recovery of different forests from these temperature-induced disturbances. This variation can lead to differences in energy and entropy dynamics, which drive the metabolic response of these systems. Using thermodynamic metrics, we quantified metabolic energy and entropy production in response to extreme heat and freeze events at three longleaf pine savanna sites spanning an edaphic moisture gradient (i.e., xeric, intermediate, mesic). The sites also differed in anthropogenic legacy, with soil tillage occurring at the intermediate site, resulting in greater woody species abundance in the understory and overstory. We found that energy reserves in this ecosystem were built during low precipitation periods and when temperatures were below 20°C. The mesic site, which had the highest plant functional diversity, exhibited an adaptive capacity to temperature extremes by maintaining low metabolic activity throughout temperature disturbances, while the intermediate and xeric sites started with high metabolic activity that gradually declined by ~15% with prolonged temperature extremes. Response to these temperature extremes was a function of hydrological drivers, as lower water availability reduced energy reserves during cold periods and photosynthetic activity during heatwaves – especially at the intermediate and xeric sites as a result of the high energy demand of oaks in the overstory. As climate change continues to alter weather patterns across the globe, it becomes increasingly important to assess metabolic resilience to greater weather variability as a function of ecosystem structure. [ABSTRACT FROM AUTHOR]