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The landscape structure of emergent wetlands in undeveloped portions of the southeastern coastal Everglades is comprised of two distinct components: scattered forest fragments, or tree islands, surrounded by a low matrix of marsh or shrub-dominated vegetation. Changes in the ma- trix, including the inland transgression of salt-tolerant man- groves and the recession of sawgrass marshes, have been attributed to the combination of sea level rise and reductions in fresh water supply. In this study we examined concurrent changes in the composition of the region's tree islands over a period of almost three decades. No trend in species com- position toward more salt-tolerant trees was observed any- where, but species characteristic of freshwater swamps increased in forests in which fresh water supply was aug- mented. Tree islands in the coastal Everglades appear to be buffered from some of the short term effects of salt water intrusion, due to their ability to build soils above the surface of the surrounding wetlands, thus maintaining mesophytic conditions. However, the apparent resistance of tree islands to changes associated with sea level rise is likely to be a temporary stage, as continued salt water intrusion will even- tually overwhelm the forests' capacity to maintain fresh water in the rooting zone.

Recently, evapotranspiration has been hypothesized to promote the secondary formation of calcium carbonate year-round on tree islands in the Everglades by influencing groundwater ions concentrations. However, the role of recharge and evapotranspiration as drivers of shallow groundwater ion accumulation has not been investigated. The goal of this study is to develop a hydrologic model that predicts the chloride concentrations of shallow tree island groundwater and to determine the influence of overlying biomass and underlying geologic material on these concentrations. Groundwater and surface water levels and chloride concentrations were monitored on eight constructed tree islands at the Loxahatchee Impoundment Landscape Assessment (LILA) from 2007 to 2010. The tree islands at LILA were constructed predominately of peat, or of peat and limestone, and were planted with saplings of native tree species in 2006 and 2007. The model predicted low shallow groundwater chloride concentrations when inputs of regional groundwater and evapotranspiration-to-recharge rates were elevated, while low evapotranspiration-to-recharge rates resulted in a substantial increase of the chloride concentrations of the shallow groundwater. Modeling results indicated that evapotranspiration typically exceeded recharge on the older tree islands and those with a limestone lithology, which resulted in greater inputs of regional groundwater. A sensitivity analysis indicated the shallow groundwater chloride concentrations were most sensitive to alterations in specific yield during the wet season and hydraulic conductivity in the dry season. In conclusion, the inputs of rainfall, underlying hydrologic properties of tree islands sediments and forest structure may explain the variation in ion concentration seen across Everglades tree islands. Copyright © 2012 John Wiley & Sons, Ltd.

Everglades tree islands are patches of woody vegetation ranging in size from 0.1 to 70 ha embedded in a marsh matrix. Tree islands are an essential component of the tree island–ridge–slough topographic continuum and the trees provide a mechanism for the accumulation of phosphorus in the landscape, enhancing landscape biocomplexity. This article reviews the literature of tree island ecology and describes the predicted effects of five ecosystem restoration scenarios on tree islands. Elevations of the highest points on 404 islands across the Everglades were used to assess the effects of the scenarios at a landscape level, while the plant communities of nine islands were modeled to assess local effects. Evaluation of the restoration scenarios were based on three critical components needed to maintain and restore tree islands: hydrology that allows the survival of woody species, seasonally appropriate water flow to move nutrients off the heads of islands, and oligotrophy. All restoration options generally improved water conditions for tree growth, although flooding of islands in some areas was predicted to increase. Scenarios with the greatest amount of decompartmentalization and largest capacity to remove phosphorus from water entering the Everglades provided the best chance of delivering vigorous pulses of sheet flow in directions parallel to historic flows and maintaining oligotrophy. Tree islands are “bellwethers” of restoration actions because their maintenance on the landscape requires multiple ecosystem functions.

Knowledge of the spatial and temporal changes caused by episodic disturbances and seasonal variability is essential for understanding the dynamics of mangrove forests at the landscape scale, and for building a baseline that allows detection of the effects of future environmental change. In combination with LiDAR data, we calculated four vegetation indices from 150 Landsat TM images from 1985 to 2011 in order to detect seasonal changes and distinguish them from disturbances due to hurricanes and chilling events in a mangrove‐dominated coastal landscape. We found that normalized difference moisture index (NDMI) performed best in identifying both seasonal and event‐driven episodic changes. Mangrove responses to chilling and hurricane events exhibited distinct spatial patterns. Severe damage from intense chilling events was concentrated in the interior dwarf and transition mangrove forests with tree heights less than 4 m, while severe damage from intense hurricanes was limited to the mangrove forest near the coast, where tree heights were more than 4 m. It took 4–7 months for damage from intense chilling events and hurricanes to reach their full extent, and took 2–6 yr for the mangrove forest to recover from these disturbances. There was no significant trend in the vegetation changes represented by NDMI over the 27‐yr period, but seasonal signals from both dwarf and fringe mangrove forests were discernible. Only severe damage from hurricanes and intense chilling events could be detected in Landsat images, while damage from weak chilling events could not be separated from the background seasonal change.

The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associate canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000 mm.yr−1 (water-limited forests) and to radiation otherwise (light-limited forests); on the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. Precipitation first-order control indicates an overall decrease in tropical forest productivity in a drier climate.

Made available in DSpace on 2018-12-11T17:02:44Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-04-28 The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000ĝ€-mmĝ€-yrĝ'1 (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest, and in current light-limited forest with future rainfall < 2000ĝ€-mmĝ€-yrĝ'1. Author(s) 2016. Remote Sensing Division National Institute for Space Research - INPE São José Dos Campos CIRAD UMR Ecologie des Forêts de Guyane INRA UMR EEF 1137 INRA UMR Ecologie des Forêts de Guyane Department of Biology University of Antwerp National Center for Monitoring and Early Warning of Natural Disasters - CEMADEN São José Dos Campos School of Geography University of Leeds Institute of Botany University of Hohenheim Laboratory for Wood Biology and Xylarium Royal Museum for Central Africa Programa de Pós-graduação em Ciências de Florestas Tropicais Instituto Nacional de Pesquisas da Amazônia Embrapa Florestas Brazilian Agricultural Research Corporation School of Biological Sciences University of Tasmania Institute of Geography University of Erlangen-Nuremberg Laboratory of Geo-information Science and Remote Sensing Wageningen University Centro de Ciências Biológicas e da Natureza Laboratóio de Botânica e Ecologia Vegetal Universidade Federal Do Acre Instituto Pirenaico de Ecologia Consejo Superior de Investigaciones Cientificas (IPE-CSIC) Instituto Boliviano de Investigacion Forestal (IBIF) Santa Cruz de la Sierra Centro de Energia Nuclear Na Agricultura Laboratóio de Ecologia Isotópica Universidade de SÃo Paulo Departamento de Botânica Universidade Federal Do Paraná Departamento de Botânica Universidade Federal de Juiz de Fora (UFJF) Programa de Pós-Graduação Ecologia e Manejo de Recursos Naturais Universidade Federal Do Acre Departamento de Ecologia Do Instituto de Biociências Universidade de São Paulo (USP) UMR 5174 Laboratoire Evolution et DiversitéBiologique CNRS and UniversitéPaul Sabatier Biological Sciences Department University of Zambia Department of Biology University of Missouri-St. Louis Coordenação de Pesquisas em Biodiversidade Instituto Nacional de Pesquisas da Amazônia Departamento de Engenharia Florestal Universidade Federal de Viçosa (UFV) Departamento de Engenharia Florestal Universidade Federal Do Paraná Centro de Ciêcias Biológicas e da Natureza Laboratório de Botânica e Ecologia Vegetal Universidade Federal Do Acre Prefeitura Municipal de Rio Branco Département Hommes Natures Sociétés Centre National de la Recherche Scientifique (CNRS) et UMR 208 Patrimoines Locaux et Gouvernance, Cedex 05 Dept. Forest and Wood Science University of Stellenbosch Meisterschule Ebern für das Schreinerhandwerk Floresta Estadual de Assis Tanzania Forestry Research Institute (TAFORI), P.O. Box Departamento de Ciências Florestais Universidade de São Paulo Escola Superior de Agricultura Luiz de Queiroz Departamento de Engenharia Florestal - DEF Universidade Estadual Do Centro-Oeste Departamento de Ciências Florestais Centro de Ciências Rurais Universidade Federal de Santa Maria Departamento de Botânica Laboratório de Fisiologia Vegeta Universidade de Brasília Instituto de Ciências Biológicas World Agroforestry Centre (ICRAF), P.O. Box Coordenação de Pesquisa em Ecologia Instituto Nacional de Pesquisas da Amazônia, C.P. 478 Departement of Land Resource Management Northern Territory Government Research Institute for Environment and Livelihoods Charles Darwin University Department of Biological Sciences Mount Holyoke College Department of Earth System Science Stanford University Department of Natural Resources and Environmental Sciences University of Illinois at Urbana Champaign Department of Plant Ecology Albrecht von Haller Institute of Plant Sciences University of Göttingen Departamento de Engenharia Florestal Universidade Do Estado de Santa Catarina - UDESC Tropical Peat Research Institute Biological Research Division Malaysian Palm Oil Board Departamento de Botânica Instituto de Ciências Biologicas Universidade Federal de Minas Gerais Division of Science and Environmental Policy California State University Monterey Bay Departamento de Biologia Universidade Federal de Sergipe Programa Forestal Colegio de Postgraduados Department of Geosciences and Geography University of Helsinki School of Geography and the Environment University of Oxford Departamento de Solos e Engenharia Agrícola Universidade Federal Do Paraná Laboratoria de Dendrochronologia y Anatomia de Maderas Espinoza Universidad Nacional de Loja Research Institute for the Environment and Livelihoods Charles Darwin University Center for Forest Disturbance Science USDA Forest Service Department of Biological Sciences Florida International University Graduate School of Agriculture Kyoto University Institut Français de Pondicherry UMR AMAP (BotAnique et BioinforMatique de l'Architecture des Plantes) IRD Tree Ring and Environmental History Laboratory Instituto Argentino de Nivología Glaciología y Ciencias Ambientales - CONICET Department of Earth and Environment Southeast Environmental Research Center Florida International University Departamento de Biologia Aplicada FCAV Universidade Estadual Paulista UNESP UR BandSEF (Biens et Services des Écosystèmes Forestiers Tropicaux) CIRAD School of Geosciences University of Edinburgh CarboForExpert HJ Andrews Experimental Forest Oregon State University Ibama PRONAT - Programa de Pós-Graduação em Recurso Naturais Universidade Federal de Roraima - UFRR School of Biological Sciences University of Aberdeen Departamento de Ciências Ambientais Universidade Federal Do Amapá Embrapa Cocais Brazilian Agricultural Research Corporation Instituto Boliviano de Investigacion Forestal (IBIF) Universidad Autonoma Gabriel René Moreno Department of Forest Vegetation Forestry and Forest Products Research Institute (FFPRI) Núcleo de Estudos e Pesquisas Ambientais (NEPAM) Universidade Estadual de Campinas (UNICAMP) Embrapa Roraima Brazilian Agricultural Research Corporation Crop Production Systems in the Tropics Georg-August-Universit Departamento de Engenharia Florestal Centro de Educação Superior Norte Universidade Federal de Santa Maria College of Life and Environmental Sciences University of Exeter Departamento de Biologia Aplicada FCAV Universidade Estadual Paulista UNESP

The Everglades is a low-nutrient ecosystem occupied by marsh plant species adapted to low avail- ability of phosphorus. Recently, however, tree islands that are scattered throughout the marsh have been recognized as biogeochemical hotspots. The goal of this study was to determine the general patterns of response by common tree species when conditions limiting to optimal growth were improved by fertilization in an experimentally con- structed and managed Everglades wetland. Thirty-six trees of two species, Annona glabra and Chrysobalanus icaco, were randomly selected on two peat- and two limestone-based islands. Each tree was treated with one of three nutrient regimes: Nitrogen (N), Phosphorus (P), or Control (no addition of nutrients). Positive highly significant P-treatment effects on leaf total P and leaf N:P were observed in both species in comparison to Control trees, but neither species exhibited a similar response to N-fertilization. However, among the two species, only A. glabra responded to P-fertilization with increased growth. Both fertilized and unfertilized trees of each species exhibited a highly significant growth re- sponse to hydrological condition, with growth enhanced on less persistently flooded sites. Our experimental results identify a clear difference in species growth responses to substrate type in the two species, but do not support the idea that a single critical N:P ratio can be used to indicate nutrient limitation for all wetland trees.

Low-elevation islands face threats from sea level rise (SLR) and increased storm intensity. Evidence of endangered species’ population declines and shifts in vegetation communities are already underway in the Florida Keys. SLR predictions indicate large areas of these habitats may be eliminated in the next century. Using the Florida Keys as a model system, we present a process for evaluating conservation options for rare and endemic taxa. Considering species characteristics and habitat, we assess central issues that influence conservation options. We contrast traditional and controversial options for two animal and two plant species giving special emphasis to perceptions of ecological risk and safety from SLR and suggest courses of action. Multiple strategies will be required to spread extinction risk and will be effective for different time periods. Global climate change presents an uncertain, perhaps no-analog future that will challenge land managers and practitioners to re-evaluate equilibrium-state-conceived laws and policies not only for these taxa, but for many facing similar threats. To embrace conservation in a changing world will require a new dialogue that includes controversial ideas, a review of existing laws and policies, and preparation for the oncoming change.

The potential impacts of sea level rise (SLR) on 95% of the land areas of the Florida Keys were estimated through analysis of a digital elevation model (DEM) derived from airborne light detection and ranging (LiDAR) measurements in a geographic information system. The topographic detail of the LiDAR DEM allowed projections of land, population, and property inundation in 0.15 m increments across a broad range of SLR scenarios for the next century. The results showed that a 0.6 m SLR by 2100 would inundate about 70% of the total land surface, but smaller percentages of the population (17%) and real property (12%). A 1.5 m rise in sea level during the same period would inundate 91% of the land surface, 71% of the population and 68% of property in the study area. Comparison of inundation dynamics indicates that the Lower Florida Keys are more susceptible to SLR than the Upper Florida Keys. The inundation dynamics exhibit non-linear behavior and demonstrate tipping points in inundation processes beyond which the inundation of land, population, and property speeds up. Acceleration of SLR will amplify the non- linear inundation, causing tipping points to be reached sooner.

We investigate the effects of Hurricane Wilma’s storm surge (23–24 October 2005) on the dominant tree Pinus elliottii var densa (South Florida slash pine) and rare plant species in subtropical pine rocklands of the Lower Florida Keys. We examine the role of elevation on species abundance in 1995 (Hurricane Betsy in 1965), 2005 (Hurricane Georges in 1998), and 2008 (Hurricane Wilma in 2005) to investigate if hurricanes influence abundance by eliminating plants at lower elevation on Big Pine Key, the largest island in the Lower Florida Keys. We compare densities before and after Hurricane Wilma over the 2005–2008 sampling period and examine the role of elevation on changes in pine and rare species densities three years after Hurricane Wilma. We use elevation to assess the impact of hurricanes because elevation determined whether a location was influenced by storm surge (maximum surge of 2 m) in the Lower Florida Keys, where pine rocklands occur at a maximum elevation of 3 m. In 1995 (30 years after a major storm), elevation did not explain the abundance of South Florida slash pine or Chamaecrista lineata, but explained significant variation in abundance of Chamaesyce deltoidea. The latter two species are rare herbaceous plants restricted to pine rocklands. In 2008, 3 years after Hurricane Wilma, the positive relationship between elevation and abundance was strongest for South Florida slash pine, C. deltoidea, and C. lineata. Effects of Hurricane Wilma were not significant for rare species with wider distribution, occurring in plant communities adjacent to pine rocklands and in disturbed rocklands. Our results suggest that hurricanes drive population dynamics of South Florida slash pine and rare species that occur exclusively in pine rocklands at higher elevations. Rare species restricted to pine rocklands showed dramatic declines after Hurricane Wilma and were eliminated at elevations

Coastal ecosystems lie at the forefront of sea level rise. We posit that before the onset of actual inundation, sea level rise will influence the species composition of coastal hardwood hammocks and buttonwood (Conocarpus erectus L.) forests of the Everglades National Park based on tolerance to drought and salinity. Precipitation is the major water source in coastal hammocks and is stored in the soil vadose zone, but vadose water will diminish with the rising water table as a consequence of sea level rise, thereby subjecting plants to salt water stress. A model is used to demonstrate that the constraining effect of salinity on transpiration limits the distribution of freshwater-dependent communities. Field data collected in hardwood hammocks and coastal buttonwood forests over 11 years show that halophytes have replaced glycophytes. We establish that sea level rise threatens 21 rare coastal species in Everglades National Park and estimate the relative risk to each

We address the relative importance of nutrient availability in relation to other physical and biological factors in determining plant community assemblages around Everglades Tree Islands (Everglades National Park, Florida, USA). We carried out a one-time survey of elevation, soil, water level and vegetation structure and composition at 138 plots located along transects in three tree islands in the Park’s major drainage basin. We used an RDA variance partitioning technique to assess the relative importance of nutrient availability (soil N and P) and other factors in explaining herb and tree assemblages of tree island tail and surrounded marshes. The upland areas of the tree islands accumulate P and show low N concentration, producing a strong island-wide gradient in soil N:P ratio. While soil N:P ratio plays a significant role in determining herb layer and tree layer community assemblage in tree island tails, nevertheless part of its variance is shared with hydrology. The total species variance explained by the predictors is very low. We define a strong gradient in nutrient availability (soil N:P ratio) closely related to hydrology. Hydrology and nutrient availability are both factors influencing community assemblages around tree islands, nevertheless both seem to be acting together and in a complex mechanism. Future research should be focused on segregating these two factors in order to determine whether nutrient leaching from tree islands is a factor determining community assemblages and local landscape pattern in the Everglades, and how this process might be affected by water management.

Spatial heterogeneity in soils is often characterized by the presence of resource-enriched patches ranging in size from a single shrub to wooded thickets. If the patches persist long enough, the primary constraint on production may transition from one limiting environmental factor to another. Tree islands that are scattered throughout the Florida Everglades basin comprise nutrient-enriched patches, or resource islands, in P-limited oligotrophic marshes. We used principal component analysis and multiple regressions to characterize the belowground environment (soil, hydrology) of one type of tree island, hardwood hammocks, and examined its relationship with the three structural variables (basal area, biomass, and canopy height) indicative of site productivity. Hardwood hammocks in the southern Everglades grow on two distinct soil types. The first, consisting of shallow, organic, relatively low-P soils, is common in the seasonally flooded Marl Prairie landscape. In contrast, hammocks on islands embedded in long hydroperiod marsh have deeper, alkaline, mineral soils with extremely high P concentrations. However, this edaphic variation does not translate simply into differences in forest structure and production. Relative water depth was unrelated to all measures of forest structure and so was soil P, but the non-carbonate component of the mineral soil fraction exhibited a strong positive relationship with canopy height. The development of P-enriched forest resource islands in the Everglades marsh is accompanied by the buildup of a mineral soil; however, limitations on growth in mature islands appear to differ substantively from those that dominate incipient stages in the transformation from marsh to forest.

The authors summarize the main findings of the Florida Coastal Everglades Long-Term Ecological Research (FCE-LTER) program in the EMER, within the context of the Comprehensive Everglades Restoration Plan (CERP), to understand how regional processes, mediated by water flow, control population and ecosystem dynamics across the EMER landscape. Tree canopies with maximum height

Mosaic freshwater landscapes exhibit tree-dominated patches —or tree islands—interspersed in a background of marshes and wet prairies. In the Florida Everglades, these patterned landscapes provide habitat for a variety of plant and animal species and are hotspots of biodiversity. Even though the emergence of patchy freshwater systems has been associated with climate histories, fluctuating hydrologic conditions, and internal feedbacks, a process-based quantitative understanding of the underlying dynamics is still missing. Here, we develop a mechanistic framework that relates the dynamics of vegetation, nutrients and soil accretion/loss through ecogeomorphic feedbacks and interactions with hydrologic drivers. We show that the stable coexistence of tree islands and marshes results as an effect of their both being (meta-) stable states of the system. However, tree islands are found to have only a limited resilience, in that changes in hydrologic conditions or vegetation cover may cause an abrupt shift to a stable marsh state. The inherent non-linear and discontinuous dynamics determining the stability and resilience of tree islands should be accounted for in efforts aiming at the management, conservation and restoration of these features.

The hydrodynamics of tree islands during the growth of newly planted trees has been found to be influenced by both vegetation biomass and geologic conditions. From July 2007 through June 2009, groundwater and surface-water levels were monitored on eight recently planted tree islands at the Loxahatchee Impoundment Landscape Assessment (LILA) facility in Boynton Beach, Florida, USA. Over the 2-year study, stand development coincided with the development of a water-table depression in the center of each of the islands that was bounded by a hydraulic divide along the edges. The water-table depression was greater in islands composed of limestone as compared to those composed of peat. The findings of this study suggest that groundwater evapotranspiration by trees on tree islands creates complex hydrologic interactions between the shallow groundwater in tree islands and the surrounding surface water and groundwater bodies.

Questions: How are the early survival and growth of seedlings of Everglades tree species planted in an experimental setting on artificial tree islands affected by hydrology and substrate type? What are the implications of these responses for broader tree island restoration efforts? Location: Loxahatchee Impoundment Landscape Assessment (LILA), Boynton Beach, Florida, USA. Methods: An experiment was designed to test hydrological and substrate effects on seedling growth and survivorship. Two islands – a peat and a limestonecore island representing two major types found in the Everglades – were constructed in four macrocosms. A mixture of eight tree species was planted on each island in March of 2006 and 2007. Survival and height growth of seedlings planted in 2006 were assessed periodically during the next two and a half years. Results: Survival and growth improved with increasing elevation on both tree island substrate types. Seedlings’ survival and growth responses along a moisture gradient matched species distributions along natural hydrological gradients in the Everglades. The effect of substrate on seedling performance showed higher survival of most species on the limestone tree islands, and faster growth on their peat-based counterparts. Conclusions: The present results could have profound implications for restoration of forests on existing landforms and artificial creation of tree islands. Knowledge of species tolerance to flooding

We present results of a rock-magnetic study of soils that were affected by wildfires that burned portions of the Everglades in the Spring of 2008. Soils at sites that were extensively burned exhibit a pronounced surface magnetic enhancement effect with magnetizations of surface samples up to 16 times greater than that observed at depth (>7 cm) at these sites. The increase in magnetization results from an increased abundance of a low-coercivity phase (maghemite) that occurs at the expense of the abundance of a high-coercivity phase (goethite). These results indicate that fire-induced heating caused goethite in the surface soils to convert into a more magnetic, low-coercivity phase, such as maghemite. Goethite is an excellent adsorber of phosphorus, and therefore we hypothesize that the destruction of goethite as a result of burning may have important implications for phosphorus cycling in the Everglades ecosystem. Copyright © 2010 John Wiley & Sons, Ltd.

The tree island hammock communities in the Florida Everglades provide one of many examples of self-organized wetland landscape. However, little is understood about why these elevated tree island communities have higher nutrient concentration than the surrounding freshwater marshes. Here we used stable isotopes and elemental analysis to compare dry season water limitation and soil and foliar nutrient status in upland hammock communities of 18 differ- ent tree islands located in the Shark River Slough and adjacent prairie landscapes. We observed that prairie tree islands, having a shorter hydroperiod, suffer greater water deficits during the dry season than slough tree islands by examining shifts in foliar d 13 C values. We also found that prairie tree islands have lower soil total phosphorus concentration and higher foliar N/P ratio than slough tree islands. Foliar d 15 N values, which often increase with greater P availabil- ity, was also found to be lower in prairie tree islands than in slough tree islands. Both the elemental N and P and foliar d 15 N results indicate that the upland hammock plant communities in slough tree islands have higher amount of P available than those in prairie tree islands. Our findings are consistent with the transpiration driven nutrient harvesting chemo- hydrodynamic model. The water limited prairie tree islands hypothetically transpire less and harvest less P from the surrounding marshes than slough tree islands during the dry season. These findings suggest that hydroperiod is important to nutrient accumula- tion of tree island habitats.

Tree islands in the Everglades wetlands are centers of biodiversity and targets of restoration, yet little is known about the pattern of water source utilization by the constituent woody plant communities: upland hammocks and flooded swamp forests. Two potential water sources exist: (1) entrapped rainwater in the vadose zone of the organic soil (referred to as upland soil water), that becomes enriched in phosphorus, and (2) phosphorus-poor groundwater/surface water (referred to as regional water). Using natural stable isotope abundance as a tracer, we observed that hammock plants used upland soil water in the wet season and shifted to regional water uptake in the dry season, while swamp forest plants used regional water throughout the year. Consistent with the previously observed phosphorus concentrations of the two water sources, hammock plants had a greater annual mean foliar phosphorus concentration over swamp forest plants, thereby supporting the idea that tree island hammocks are islands of high phosphorus concentrations in the oligotrophic Everglades. Foliar nitrogen levels in swamp forest plants were higher than those of hammock plants. Linking water sources with foliar nutrient concentrations can indicate nutrient sources and periods of nutrient uptake, thereby linking hydrology with the nutrient regimes of different plant communities in wetland ecosystems. Our results are consistent with the hypotheses that (1) over long periods, upland tree island communities incrementally increase their nutrient concentration by incorporating marsh nutrients through transpiration seasonally, and (2) small differences in micro-topography in a wetland ecosystem can lead to large differences in water and nutrient cycles.

The distribution of mangrove biomass and forest structure along Shark River estuary in the Florida Coastal Everglades (FCE) has been correlated with elevated total phosphorus concentration in soils thought to be associated with storm events. The passage of Hurricane Wilma across Shark River estuary in 2005 allowed us to quantify sediment deposition and nutrient inputs in FCE mangrove forests associated with this storm event and to evaluate whether these pulsing events are sufficient to regulate nutrient biogeochemistry in mangrove forests of south Florida. We sampled the spatial pattern of sediment deposits and their chemical properties in mangrove forests along FCE sites in December 2005 and October 2006. The thickness (0.5 to 4.5 cm) of hurricane sediment deposits decreased with distance inland at each site. Bulk density, organic matter content, total nitrogen (N) and phosphorus (P) concentrations, and inorganic and organic P pools of hurricane sediment deposits differed from surface (0–10 cm) mangrove soils at each site. Vertical accretion resulting from this hurricane event was eight to 17 times greater than the annual accretion rate (0.30 ± 0.03 cm year−1) averaged over the last 50 years. Total P inputs from storm-derived sediments were equivalent to twice the average surface soil nutrient P density (0.19 mg cm−3). In contrast, total N inputs contributed 0.8 times the average soil nutrient N density (2.8 mg cm−3). Allochthonous mineral inputs from Hurricane Wilma represent a significant source of sediment to soil vertical accretion rates and nutrient resources in mangroves of southwestern Everglades. The gradient in total P deposition to mangrove soils from west to east direction across the FCE associated with this storm event is particularly significant to forest development due to the P-limited condition of this carbonate ecosystem. This source of P may be an important adaptation of mangrove forests in the Caribbean region to projected impacts of sea-level rise.

Sea-level rise presents an imminent threat to freshwater-dependent ecosystems on small oceanic islands, which often harbor rare and endemic taxa. Conservation of these assemblages is complicated by feedbacks between sea level and recurring pulse disturbances (eg hurricanes, fire). Once sea level reaches a critical level, the transition from a landscape characterized by mesophytic upland forests and freshwater wetlands to one dominated by mangroves can occur suddenly, following a single storm-surge event. We document such a trajectory, unfolding today in the Florida Keys. With sea level projected to rise substantially during the next century, ex-situ actions may be needed to conserve individual species of special concern. However, within existing public conservation units, managers have a responsibility to conserve extant biodiversity. We propose a strategy that combines the identification and intensive management of the most defensible core sites within a broader reserve system, in which refugia for biota facing local extirpation may be sought.

Freeze events significantly influence landscape structure and community composition along subtropical coastlines. This is particularly true in south Florida, where such disturbances have historically contributed to patch diversity within the mangrove forest, and have played a part in limiting its inland transgression. With projected increases in mean global temperatures, such instances are likely to become much less frequent in the region, contributing to a reduction in heterogeneity within the mangrove forest itself. To understand the process more clearly, we explored the dynamics of a Dwarf mangrove forest following two chilling events that produced freeze-like symptoms, i.e., leaf browning, desiccation, and mortality, and interpreted the resulting changes within the context of current winter temperatures and projected future scenarios. Structural effects from a 1996 chilling event were dramatic, with mortality and tissue damage concentrated among individuals comprising the Dwarf forest’s low canopy. This disturbance promoted understory plant development and provided an opportunity for Laguncularia racemosa to share dominance with Rhizophora mangle. Mortality due to the less severe 2001 event was greatest in the understory, probably because recovery of the protective canopy following the earlier freeze was still incomplete. Stand dynamics were static over the same period in nearby unimpacted sites. The probability of reaching temperatures as low as those recorded at a nearby meteorological station ( 31C) under several warming scenarios was simulated by applying 11 incremental temperature increases to a model developed from a 42-year temperature record. According to the model, the frequency of similar chilling events decreased from once every 1.9 years at present to once every 3.4 and 32.5 years with 1 and 41C warming, respectively. The large decrease in the frequency of these events would eliminate an important mechanism that maintains Dwarf forest structure, and promotes compositional diversity.

Sal (Shorea robusta) forest is found in an extensive array of conditions in lowland Nepal, and has been heavily used by both government and local people. Thus, we did a study to provide information on sal forests occupying a broad range of historical and environmental influences across anextensiverangeinthewesternTerai ofNepaland explorefactors‐bothenvironmentaland anthropogenic‐that mayberesponsibleforvariation of forest structure. Trees, saplings, seedlings and shrubs were sampled along transects (2 km long) in two protected areas and two proposed community forests. The protected areas had three transects each, and a single transect covered two proposed community forests. Samplings were done every 200 m along the transects, a plotless technique sampled trees (>5 cm dbh). With tree sampling point as the center, shrubs and saplings (1‐5 cm dbh and >1 m height) were sampled in 5 m radius circular plots and herbs and seedlings (

Extensive portions of the southern Everglades are characterized by series of elongated, raised peat ridges and tree islands oriented parallel to the predominant flow direction, separated by intervening sloughs. Tall herbs or woody species are associated with higher elevations and shorter emergent or floating species are associated with lower elevations. The organic soils in this “Ridge-and-Slough” landscape have been stable over millennia in many locations, but degrade over decades under altered hydrologic conditions. We examined soil, pore water, and leaf phosphorus (P) and nitrogen (N) distributions in six Ridge and Slough communities in Shark Slough, Everglades National Park. We found P enrichment to increase and N to decrease monotonically along a gradient from the most persistently flooded sloughs to rarely flooded ridge environments, with the most dramatic change associated with the transition from marsh to forest. Leaf N:P ratios indicated that the marsh communities were strongly P-limited, while data from several forest types suggested either N-limitation or co-limitation by N and P. Ground water stage in forests exhibited a daytime decrease and partial nighttime recovery during periods of surface exposure. The recovery phase suggested re-supply from adjacent flooded marshes or the underlying aquifer, and a strong hydrologic connection between ridge and slough. We therefore developed a simple steady-state model to explore a mechanism by which a phosphorus conveyor belt driven by both evapotranspiration and the regional flow gradient can contribute to the characteristic Ridge and Slough pattern. The model demonstrated that evapotranspiration sinks at higher elevations can draw in low concentration marsh waters, raising local soil and water P concentrations. Focusing of flow and nutrients at the evapotranspiration zone is not strong enough to overcome the regional gradient entirely, allowing the nutrient to spread downstream and creating an elongated concentration plume in the direction of flow. Our analyses suggest that autogenic processes involving the effects of initially small differences in topography, via their interactions with hydrology and nutrient availability, can produce persistent physiographic patterns in the organic sediments of the Everglades.

We determined the rate of migration of coastal vegetation zones in response to salt-water encroachment through paleoecological analysis of mollusks in 36 sediment cores taken along transects perpendicular to the coast in a 5.5 km2 band of coastal wetlands in southeast Florida. Five vegetation zones, separated by distinct ecotones, included freshwater swamp forest, freshwater marsh, and dwarf, transitional and fringing mangrove forest. Vegetation composition, soil depth and organic matter content, porewater salinity and the contemporary mollusk community were determined at 226 sites to establish the salinity preferences of the mollusk fauna. Calibration models allowed accurate inference of salinity and vegetation type from fossil mollusk assemblages in chronologically calibrated sediments. Most sediments were shallow (20–130 cm) permitting coarse-scale temporal inferences for three zones: an upper peat layer (zone 1) representing the last 30–70 years, a mixed peat-marl layer (zone 2) representing the previous ca. 150–250 years and a basal section (zone 3) of ranging from 310 to 2990 YBP. Modern peat accretion rates averaged 3.1 mm yr−1 while subsurface marl accreted more slowly at 0.8 mm yr−1. Salinity and vegetation type for zone 1 show a steep gradient with freshwater communities being confined west of a north–south drainage canal constructed in 1960. Inferences for zone 2 (pre-drainage) suggest that freshwater marshes and associated forest units covered 90% of the area, with mangrove forests only present along the peripheral coastline. During the entire pre-drainage history, salinity in the entire area was maintained below a mean of 2 ppt and only small pockets of mangroves were present; currently, salinity averages 13.2 ppt and mangroves occupy 95% of the wetland. Over 3 km2 of freshwater wetland vegetation type have been lost from this basin due to salt-water encroachment, estimated from the mollusk-inferred migration rate of freshwater vegetation of 3.1 m yr−1 for the last 70 years (compared to 0.14 m yr−1 for the pre-drainage period). This rapid rate of encroachment is driven by sea-level rise and freshwater diversion. Plans for rehydrating these basins with freshwater will require high-magnitude re-diversion to counteract locally high rates of sea-level rise.

Over the last one hundred years, compartmentalization and water management activities have reduced water flow to the ridge and slough landscape of the Everglades. As a result, the once corrugated landscape has become topographically and vegetationally uniform. The focus of this study was to quantify variation in surface flow in the ridge and slough landscape and to relate flow conditions to particulate transport and deposition. Over the 2002–2003 and 2003–2004 wet seasons, surface velocities and particulate accumulation were measured in upper Shark River Slough in Everglades National Park. Landscape characteristics such as elevation, plant density and biomass also were examined to determine their impact on flow characteristics and material transport. The results of this study demonstrate that the release of water during the wet season not only increases water levels, but also increased flow speeds and particulate transport and availability. Further, flow speeds were positively and significantly correlated with water level thereby enhancing particulate transport in sloughs relative to ridges especially during peak flow periods. Our results also indicate that the distribution of biomass in the water column, including floating plants and periphyton, affects velocity magnitude and shape of vertical profiles, especially in the sloughs where Utricularia spp. and periphyton mats are more abundant. Plot clearing experiments suggest that the presence of surface periphyton and Utricularia exert greater control over flow characteristics than the identity (i.e., sawgrass or spike rush) or density of emergent macrophytes, two parameters frequently incorporated into models describing flow through vegetated canopies. Based on these results, we suggest that future modeling efforts must take the presence of floating biomass, such as Utricularia, and presence of periphyton into consideration when describing particulate transport.

Summary Tree islands in the Shark River Slough of the Everglades National Park (ENP), in the southern state of Florida in the United States, are part of a wetland system of densely vegetated ridges interspersed within relatively open sloughs. Human alteration of this system has had dramatic negative effects on the landscape of the region and restoration efforts will require adjusting the hydrology of the region to assure the preservation of these important ecologic features. The primary objectives of this study were to document the hydrology in the vicinity of tree islands in ENP by measuring velocities in time and space and by characterizing suspended sediments. The results of such measurements were interpreted with respect to factors that may limit tree island growth. The measurements were conducted in the vicinity of three tree islands known as Black Hammock (BH), Gumbo Limbo (GL), and an unnamed island that was named for this study as Satin Leaf (SL). Acoustical Doppler Velocity (ADV) meters were used for measuring the low velocities of the Everglades water flow. Properties of suspended sediments were characterized through measurements of particle size distribution, turbidity, concentration and particle density. Mean velocities observed at each of the tree islands varied from 0.9 to 1.4 cm/s. Slightly higher mean velocities were observed during the wet season (1.2–1.6 cm/s) versus the dry season (0.8–1.3 cm/s). Maximum velocities of more than 4 cm/s were measured in areas of Cladium jamaicense die-off and at the hardwood hammock (head) of the islands. At the island’s head, water is channelized around obstructions such as tree trunks in relatively rapid flow, which may limit the lateral extent of tree island growth. Channelization is facilitated by shade from the tree canopy, which limits the growth of underwater vegetation thereby minimizing the resistance to flow and limiting sediment deposition. Suspended sediment concentrations were low (0.5–1.5 mg/L) at all study sites and were primarily of organic origin. The mean particle size of the suspended sediments was 3 μm with a distribution that was exponential. Critical velocities needed to cause re-suspension of these particles were estimated to be above the actual velocities observed. Sediment transport within the water column appears to be at a near steady state during the conditions evaluated with low rates of sediment loss balanced by presumably the release of equivalent quantities of particles of organic origin. Existing hydrologic conditions do not appear to transport sufficient suspended sediments to result in the formation of tree islands. Of interest would be to collect hydrologic and sediment transport data during extreme hydrologic events to determine if enough sediment is transported under these conditions to promote sufficient sediment accumulations.

We analyzed the dynamics of freshwater marsh vegetation of Taylor Slough in eastern Everglades National Park for the 1979 to 2003 period, focusing on cover of individual plant species and on cover and composition of marsh communities in areas potentially influenced by a canal pump station (“S332”) and its successor station (“S332D”). Vegetation change analysis incorporated the hydrologic record at these sites for three intervals: pre-S332 (1961–1980), S332 (1980–1999), post-S332 (1999–2002). During S332 and post-S332 intervals, water level in Taylor Slough was affected by operations of S332 and S332D. To relate vegetation change to plot-level hydrological conditions in Taylor Slough, we developed a weighted averaging regression and calibration model (WA) using data from the marl prairies of Everglades National Park and Big Cypress National Preserve. We examined vegetation pattern along five transects. Transects 1–3 were established in 1979 south of the water delivery structures, and were influenced by their operations. Transects 4 and 5 were established in 1997, the latter west of these structures and possibly under their influence. Transect 4 was established in the northern drainage basin of Taylor Slough, beyond the likely zones of influence of S332 and S332D. The composition of all three southern transects changed similarly after 1979. Where muhly grass (Muhlenbergia capillaris var. filipes) was once dominant, sawgrass (Cladium jamaicense), replaced it, while where sawgrass initially predominated, hydric species such as spikerush (Eleocharis cellulosa Torr.) overtook it. Most of the changes in species dominance in Transects 1–3 occurred after 1992, were mostly in place by 1995–1996, and continued through 1999, indicating how rapidly vegetation in seasonal Everglades marshes can respond to hydrological modifications. During the post-S332 period, these long-term trends began reversing. In the two northern transects, total cover and dominance of both muhly grass and sawgrass increased from 1997 to 2003. Thus, during the 1990’s, vegetation composition south of S332 became more like that of long hydroperiod marshes, but afterward it partially returned to its 1979 condition, i.e., a community characteristic of less prolonged flooding. In contrast, the vegetation change along the two northern transects since 1997 showed little relationship to hydrologic status.

Twelve tree species common in Everglades tree islands were subjected to three hydrologic regimes under controlled conditions for 25 weeks and assessed for growth and physiological responses. Treatments representing high, low, and no flood were maintained in pools of water to mimic seasonal variation in water depths at different positions in tree islands. Soil inundation under the high flood treatment resulted in reduced tree growth (height, basal diameter, crown volume) that was more pronounced and occurred earlier in mesic forest species than in swamp forest species. Physiological responses differed less among species, although stomatal conductance was a better predictor of the effects of flood stress on growth than either relative water content or chlorophyll fluorescence (Fv/Fm). Some swamp species appeared to be better adapted to rising water levels than others; Annona glabra, Morella cerifera, and Salix caroliniana responded more positively to flooding, while Magnolia virginiana, Persea borbonia, Chrysobalanus icaco, and Ilex cassine were less flood-tolerant. The highest mortalities and lowest growth were observed in the five upland species: Bursera simaruba, Coccoloba diversifolia, Eugenia axillaris, Sideroxylon foetidissimum, and Simarouba glauca. Of these, Sideroxylon and Simarouba did not survive to the end of the study under the high flood treatment. The moist soil conditions simulated by the low flood treatment resulted in greater growth in all species compared to soil inundation under high flood, except for the most flood-tolerant (Annona, Morella, Salix). The arrangement of species according to their responses to experimental flooding roughly paralleled their spatial distribution in the tree islands. The gradient in species responses demonstrated in this experiment may help guide responsible water management and tree island restoration in the Everglades.

Modifications of the hydrology of the Florida Everglades began in the 1880s. Impacts due to changes in the hydrological regime, as well as nutrient enrichment are clear in the northern Everglades. Although these changes were more subtle in the southern Everglades, altered hydroperiods and plant communities are targeted for restoration. Identification of restoration goals requires knowledge of past conditions, but detailed vegetation surveys prior to the pre-drainage era are lacking. Palynological studies can help fill this void. Interpretations based upon pollen and plant spores alone are limited by low pollen production of the dominant marsh species and low plant diversity in the ecosystem. In some regions the occurrence of other microfossils present in palynological preparations has been used to help interpret hydrological regimes and nutrient status and here we explore that potential for paleoecological records from the Everglades. In this study we report the distribution of various microfossils found within pollen zones identified in sediments cored from three tree islands in Shark River Slough, Everglades National Park. Using published modern pollen analogues we classified paleovegetation zones as slough, sawgrass marsh, tree island or tree island edge and documented the abundances of microfossils of algae, fungi, cyanobacteria and testate amoebae. Tree island zones, indicative of relatively short hydroperiods, were characterized by highest abundances of fungal material, testate amoebae and the base of the deposits, by the cyanobacterium, Gloeotrichia. Much of the fungal material appears to be associated with plant roots, and the mycorrhizal Glomus is locally abundant. The taxonomic affinity of the testate amoebae has not been determined, but some were arcellaceous forms that included charcoal particles in their tests. Gloeotrichia also is found in marsh and slough deposits. Its occurrence in the latter probably signals minimal water depth. Botryococcus and Zynemataceae zygospores are found in all deposits, but are less abundant in the tree island deposits. Both groups are probably part of the periphyton flora, but Botryococcus has not been recorded in phycological studies of the Everglades. Observation of these algae in the seasonally dry Everglades is consistent with other studies where they have been reported to represent shallow, slow moving waters, but inconsistent with the assumptions of meso- or eutrophic conditions commonly made in other studies. Our observation of the alga Botryoccocus and the meroplanktonic cyanobacterium Gloeotrichia in the historically oligotrophic Everglades challenges their status as indicators of nutrient enrichment.

We examined the immediate effects of a hurricane (Hurricane Andrew, August 1992) in a coastal landscape in sub-tropical Florida, and then monitored stand recovery in Fringe mangrove sites of different productive capacity for 9 years after the disturbance. Structural impacts of the hurricane were confined almost entirely to forests within 200–300 m of the coast. Mortality and damage were concentrated on canopy individuals. Following the hurricane, rapid canopy recovery and the early onset of competition among Fringe forest stems, as evidenced by relatively high mortality of smaller individuals, magnified the initial dominance of hurricane survivors and early-established seedlings over later cohorts, and limited recruitment to the brief period prior to canopy closure. Changes in the relative abundance of the two dominant mangrove species following disturbance varied strongly along the productivity gradient. The shade-tolerant Rhizophora mangle L. generally became the overwhelming canopy dominant in the competitive environment of the recovering Coastal Fringe forest following hurricane, but the shade-intolerant Laguncularia racemosa (L.) C.F. Gaertn was better represented in less productive Interior Fringe sites, where canopy closure was delayed. Site productivity is an important determinant of the success of mangrove species during post-hurricane stand development, and consequently of the zonation of communities in the coastal landscape.

We produced a landscape scale map of mean tree height in mangrove forests in Everglades National Park (ENP) using the elevation data from the Shuttle Radar Topography Mission (SRTM). The SRTM data was calibrated using airborne lidar data and a high resolution USGS digital elevation model (DEM). The resulting mangrove height map has a mean tree height error of 2.0 m (RMSE) over a pixel of 30 m. In addition, we used field data to derive a relationship between mean forest stand height and biomass in order to map the spatial distribution of standing biomass of mangroves for the entire National Park. The estimation showed that most of the mangrove standing biomass in the ENP resides in intermediate-height mangrove stands around 8 m. We estimated the total mangrove standing biomass in ENP to be 5.6 � 10 9 kg.

Species-specific allometric equations that provide estimates of biomass from measured plant attributes are currently unavailable for shrubs common to South Florida pine rocklands, where fire plays an important part in shaping the structure and function of ecosystems. We developed equations to estimate total aboveground biomass and fine fuel of 10 common hardwood species in the shrub layer of pine forests of the lower Florida Keys. Many equations that related biomass categories to crown area and height were significant (p < 0.05), but the form and variables comprising the best model varied among species. We applied the best-fit regression models to structural information from the shrub stratum in 18 plots on Big Pine Key, the most extensive pine forest in the Keys. Estimates based on species-specific equations indicated clearly that total aboveground shrub biomass and shrub fine fuel increased with time since last fire, but the relationships were non-linear. The relative proportion of biomass constituted by the major species also varied with stand age. Estimates based on mixed-species regressions differed slightly from estimates based on species-specific models, but the former could provide useful approximations in similar forests where speciesspecific regressions are not yet available. # 2004 Elsevier B.V. All rights reserved.

Recent research makes clear that much of the Everglade’s flora and fauna have evolved to tolerate or require frequent fires. Nevertheless, restoration of the Everglades has thus far been conceptualized as primarily a water reallocation project. These two forces are directly linked by the influence of water flows on fire fuel moisture content, and are indirectly linked through a series of complex feedback loops. This interaction is made more complex by the alteration and compartmentalization of current water flows and fire regimes, the lack of communication between water and fire management agencies, and the already imperiled state of many local species. It is unlikely, therefore, that restoring water flows will automatically restore the appropriate fire regimes, leaving the prospect of successful restoration in some doubt. The decline of the Cape Sable seaside sparrow, and its potential for recovery, illustrates the complexity of the situation.

The hydrologic regime of Shark Slough, the most extensive long hydroperiod marsh in Everglades National Park, is largely controlled by the location, volume, and timing of water delivered to it through several control structures from Water Conservation Areas north of the Park. Where natural or anthropogenic barriers to water flow are present, water management practices in this highly regulated system may result in an uneven distribution of water in the marsh, which may impact regional vegetation patterns. In this paper, we use data from 569 sampling locations along five cross-Slough transects to examine regional vegetation distribution, and to test and describe the association of marsh vegetation with several hydrologic and edaphic parameters. Analysis of vegetation:environment relationships yielded estimates of both mean and variance in soil depth, as well as annual hydroperiod, mean water depth, and 30-day maximum water depth within each cover type during the 1990's. We found that rank abundances of the three major marsh cover types (Tall Sawgrass, Sparse Sawgrass, and Spikerush Marsh) were identical in all portions of Shark Slough, but regional trends in the relative abundance of individual communities were present. Analysis also indicated clear and consistent differences in the hydrologic regime of three marsh cover types, with hydroperiod and water depths increasing in the order Tall Sawgrass < Sparse Sawgrass < Spikerush Marsh. In contrast, soil depth decreased in the same order. Locally, these differences were quite subtle; within a management unit of Shark Slough, mean annual values for the two water depth parameters varied less than 15 cm among types, and hydroperiods varied by 65 days or less. More significantly, regional variation in hydrology equaled or exceeded the variation attributable to cover type within a small area. For instance, estimated hydroperiods for Tall Sawgrass in Northern Shark Slough were longer than for Spikerush Marsh in any of the other regions. Although some of this regional variation may reflect a natural gradient within the Slough, a large proportion is the result of compartmentalization due to current water management practices within the marsh. We conclude that hydroperiod or water depth are the most important influences on vegetation within management units, and attribute larger scale differences in vegetation pattern to the interactions among soil development, hydrology and fire regime in this pivotal portion of Everglades.

Soils and aboveground production in five types of upland forest in the Florida Keys were examined. Throughout the habitat gradient represented by these forest types, the soils were predominantly shallow and organic, forming in place directly on the limestone bedrock. However, the well-drained soils in the most productive broadleaved forests were deep enough to qualify as Histosols (Folists). Soils decreased in electrical conductivity and increased in nutrient content with increasing aboveground production. At 3–12 Mg ha−1 yr−1, production was within the range reported for dry tropical forests. Measured rates of decomposition were moderate or fast, and estimates of the organic C turnover of several soils based on their bomb radiocarbon signature were 100 years or less. In the face of these rapid turnover rates, we attribute the development of organic soils to the absence of mineral residues from weathering of the underlying limestone bedrock. Fast turnover of organic matter, and rapid and efficient cycling of nutrients are necessary to sustain the high production rates obtained on these shallow organic soils.

Total above-ground production isusually estimated by a combination of allometry andlitter collection. However, in coastal sites that aretidally influenced, or in juvenile or dwarf forestswhere the crown bases of dominant individuals maybegin within a few decimeters of ground level,estimates of community leaf production that depend onlitter collection may not be feasible. Thus, in thispaper, we present 1) allometric equations that allowaccurate estimation of total above-ground biomass ofthree mangrove species (Rhizophora mangle, Laguncularia racemosa, and Avicennia germinans)in very small to medium size classes, and 2) analternative method of estimating total above-groundproduction that overcomes the limitations of littercollection. The method we employ to estimate mangroveproductivity is an adaptation for woody plantcommunities of a procedure introduced by Dai andWeigert (1996) for grasslands. It incorporates adetailed census of all individuals within fixedsampling plots, along with periodic observations ofmarked leaf cohorts. The method allows the comparisonof biomass allocation patterns among forests thatdiffer widely in physiognomy and physiographicsetting.The method was applied to a South Florida fringemangrove forest in the early stages of recovery fromHurricane Andrew (August 1992), and an adjacent dwarfforest which was not substantially damaged by thestorm. Total above-ground production in the fringeforest from July 1996 through June 1997 was about 3times higher than dwarf forest production,26.1 Mg·ha-1·yr-1 vs.8.1 Mg·ha-1·yr-1, respectively. Furthermore, when compared to the dwarf forest, fringeproduction rates were approximately eight, six, six,and two times as high as dwarf forest rates forproproots, branches, stems, and leaves, respectively. Calculations of leaf production were based on mean redmangrove leaf longevities that ranged from about 189days to 281 days, depending on cohort and site.Repeated measures analysis of variance indicated thatleaf life spans did not differ significantly betweendwarf and fringe forests, but did differ among leafcohorts.Based on reported values for similar mangrove forests,the method provided reasonable estimates ofabove-ground biomass and production, while furnishingrelevant auxiliary information on spatial and temporalvariation in leaf demographic patterns. Furthermore,the partitioning of annual production between woodytissues and leaves followed the reported trend in mostforest ecosystems.

To help define nitrogen (N) sources and patterns of N processing in mangrove ecosystems, mangrove leaf nitrogen contents and δ15N values were assayed in three marshes along the south Florida coast. In each marsh, leaf samples were collected from dwarf mangroves at interior locations and taller mangroves at the ocean fringe. Leaf % N and δ15N values did not differ consistently between dwarf and tall mangroves, even though there were large variations in δ15N (18‰ range, −5 to +13‰) and % N (1·2% range, 0·9–2·1%). Highest % N and δ15N values occurred along the western margin of Biscayne Bay where canals draining agricultural lands deliver high-nitrate waters to fringing mangrove marshes. High mangrove δ15N values may be good biomonitors of anthropogenic N loading to south Florida estuaries. Lower values likely reflect less anthropogenic N entering the mangrove marshes, as well as differences in plant physiology that occur along the fringe-dwarf gradient.

We examined the vegetation of the Southeast Saline Everglades (SESE), where water management and sea level rise have been important ecological forces during the last 50 years. Marshes within the SESE were arranged in well-defined compositional zones parallel to the coast, with mangrove-domi- nated shrub communities near the coast giving way to graminoid- mangrove mixtures, and then Cladium marsh. The compositional gradient was accompanied by an interiorward decrease in total aboveground biomass, and increases in leaf area index and periphyton biomass. Since the mid-1940s, the boundary of the mixed graminoid-mangrove and Cladium communities shifted inland by 3.3 km. The interior boundary of a low-productivity zone appearing white on both black-and-white and CIR photos moved inland by 1.5 km on average. A smaller shift in this 'white zone' was observed in an area receiving fresh water overflow through gaps in one of the SESE canals, while greater change occurred in areas cut off from upstream water sources by roads or levees. These large-scale vegetation dynamics are appar- ently the combined result of sea level rise - ca. 10 cm since 1940 - and water management practices in the SESE.

Forests dominated by Pinus elliottii var densa have undergone a reduction in area in the Florida Keys (USA). A previous investigation interpreted the presence of halophytic species in a former pine forest in Key Largo as evidence of sea-level rise. We therefore examined aerial photos and field evidence to learn how the 15-cm rise in local sea level over the last 70 yr had affected the distribution of pines on a second island, where intact pine forests still remained in 1991. The distribution of in situ dead pine stems showed that the area occupied by pines on Sugarloaf Key was 88 ha at some time prior to the earliest available aerial photographs, in 1935. The area of pine forest was reduced to 46 ha by 1935, and continued to decrease through 1991, when it covered 30 ha. The pattern of pine mortality was related to topographic position, with the areas where pines died earliest occupying the lowest elevations. Our analysis of current vegetation patterns showed that the areas of earliest pine mortality are now populated by a higher proportion of halophytic plant assemblages than areas of more recent pine mortality. We also compared the physiological responses of pines in two portions of the island: one where pine forest reduction had been most pronounced, and a second where the extent of the forest had changed little over the past 50 yr. Both groundwater and soil water salinity were higher in the area of rapid pine forest reduction, and the pines sampled there exhibited higher physiological stress, as indicated by pre-dawn water potential and stemwood carbon isotope ratios. These results suggest that the salinization of ground- and soil water that occurs as sea level rises is a major factor in the reduction of pine forests of Sugarloaf Key. If sea level continues to increase, the Florida Keys will experience a decline in both landscape and species diversity, as species-rich upland communities are replaced by simpler mangrove communities. This pattern may also occur in other low-lying island ecosystems with limited freshwater resources.

In south Florida, tropical hardwood forests (hammocks) occur in Everglades tree islands and as more extensive forests in coastal settings in the nearby Florida Keys. Keys hammocks have been less disturbed by humans, and many qualify as “old-growth,” while Everglades hammocks have received much heavier use. With improvement of tree island condition an important element in Everglades restoration efforts, we examined stand structure in 23 Keys hammocks and 69 Everglades tree islands. Based on Stand Density Index and tree diameter distributions, many Everglades hammocks were characterized by low stocking and under-representation in the smaller size classes. In contrast, most Keys forests had the dense canopies and open understories usually associated with old-growth hardwood hammocks. Subject to the same caveats that apply to off-site references elsewhere, structural information from mature Keys hammocks can be helpful in planning and implementing forest restoration in Everglades tree islands. In many of these islands, such restoration might involve supplementing tree stocking by planting native trees to produce more complete site utilization and a more open understory.

In fire-dependent forests, managers are interested in predicting the consequences of prescribed burning on postfire tree mortality. We examined the effects of prescribed fire on tree mortality in Florida Keys pine forests, using a factorial design with understory type, season, and year of burn as factors. We also used logistic regression to model the effects of burn season, fire severity, and tree dimensions on individual tree mortality. Despite limited statistical power due to problems in carrying out the full suite of planned experimental burns, associations with tree and fire variables were observed. Post-fire pine tree mortality was negatively correlated with tree size and positively correlated with char height and percent crown scorch. Unlike post-fire mortality, tree mortality associated with storm surge from Hurricane Wilma was greater in the large size classes. Due to their influence on population structure and fuel dynamics, the size-selective mortality patterns following fire and storm surge have practical importance for using fire as a management tool in Florida Keys pinelands in the future, particularly when the threats to their continued existence from tropical storms and sea level rise are expected to increase.

Predawn water potential of representative plant species, together with stable isotope composition of stem water and potential water sources were investigated in four low-elevation tropical hardwood hammocks in the Lower Florida Keys, during a one year period. Hammock species had the lowest water potentials when soil water content was low and/or soil salinity was high, but differences in groundwater salinity had no effect on the water potential. Comparison of D/H ratio of plant stem water with soil and ground water corroborates the conclusion that they are primarily utilizing soil water and not groundwater. Thus, tropical hardwood hammocks are buffered from saline groundwater, and are able to thrive in areas where groundwater salinity is as high as 25‰. The effect of sea level rise on these forests may depend more on changes in the frequency of tidal inundation of the soil surface than on changes in groundwater salinity.

Salinity and isotope ratios were determined in water from several wells in the Florida Keys, and tidal inlets. Both D/H and 18O/16O ratios of water from wells and tidal inlets were highly correlated to their salinity. Water from standing pools was enriched in deuterium and oxygen-18 relative to their salinity because of evaporation processes. 18O/16O and D/H ratios of stem water from plants of several different communities at Sugar Loaf Key, ranging from hardwood hammocks to mangroves, were highly correlated to their predawn water potential. The correlation was consistent with the presence of high salinity in waters with high 18O and D content. Most individuals from each community were either utilizing water with isotopic characteristics typical of freshwater or of ocean water, while only a few individuals had stem water with isotopic ratios intermediate to these two water sources.

Airborne light detection and ranging (LIDAR) measurements derived before and after Hurricanes Katrina and Wilma (2005) were used to quantify the impact of hurricanes and lightning strikes on the mangrove forest at two sites in Everglades National Park (ENP). Analysis of LIDAR measurements covering 61 and 68 ha areas of mangrove forest at the Shark River and Broad River sites showed that the proportion of high tree canopy detected by the LIDAR after the 2005 hurricane season decreased significantly due to defoliation and breakage of branches and trunks, while the proportion of low canopy and the ground increased drastically. Tall mangrove forests distant from tidal creeks suffered more damage than lower mangrove forests adjacent to the tidal creeks. The hurricanes created numerous canopy gaps, and the number of gaps per square kilometer increased from about 400~500 to 4000 after Katrina and Wilma. The total area of gaps in the forest increased from about 1~2% of the total forest area to 12%. The relative contribution of hurricanes to mangrove forest disturbance in ENP is at least 2 times more than that from lightning strikes. However, hurricanes and lightning strikes disturb the mangrove forest in a related way. Most seedlings in lightning gaps survived the hurricane impact due to the protection of trees surrounding the gaps, and therefore provide an important resource for forest recovery after the hurricane. This research demonstrated that LIDAR is an effective remote sensing tool to quantify the effects of disturbances such as hurricanes and lightning strikes in the mangrove forest.

Remote sensing technologies have provided valuable data for landscape modeling, vegetation mapping and comprehensive studies of ecosystems. Airborne laser mapping or LIDAR (Light Detection and Ranging) can directly measure the three dimensional structure of plant canopies, as well as, provide accurate digital terrain models (DTM). While temperate and boreal pine forests have been studied using these methods, very limited work has been done in subtropical pine forests. In this study, airborne LIDAR was used to characterize the three dimensional structure of the forest on Long Pine Key at Everglades National Park. Analysis of the vertical distribution of airborne LIDAR data points has shown that distinctive patterns can be described which are characteristic of the vegetation communities and transition zones for pine forests , hammocks and marshes. This information is a valuable resource for forest managers by providing landscape structural data over large areas.

In this paper we describe a methodology to map mangrove forests in 3D in the Caribbean region. We used shuttle radar topography mission (SRTM) elevation, lidar and field data to estimate mangrove mean tree height at the landscape scale. This paper emphasizes two regions which are undergoing ecosystem restoration activities: The Everglades National Park, USA and Cienaga Grande de Santa Marta, Colombia. In these regions we used, respectively, airborne and spaceborne (ICEsat (ice, cloud,and land elevation satellite )) lidar data to calibrate SRTM data and estimate mean tree height. Our results show the method is accurate if mangrove forest canopy vertical structure is well characterized.

In this paper we present a method using airborne laser mapping data to describe the vertical structure of a coastal mangrove forest in southeastern Florida. Mangroves are critical to coastal processes and the maintenance of vital habitats; however they are also highly threatened due to coastal development and rising sea levels. Access to mangroves for detailed ground surveys is extremely difficult due to dense vegetation and lack of stable ground in the tidal zone. Airborne laser mapping can provide accurate measurements of vegetation structure over large areas without the logistical difficulties of extensive ground surveys. In our method we derive frequency height histograms from the laser mapping data followed by the creation of image objects from areas sharing similar vertical height profiles. These image objects are classified based on their vertical height profiles and related to heights of mangrove forest communities obtained from field surveys. We show that airborne laser mapping technology can be used to classify mangrove forests and to study the spatial relationships among the different forest types.