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Naturally formed forest patches known as tree islands are found within lower-statured wetland matrices throughout the world, where they contrast sharply with the surrounding vegetation. In some coastal wetlands they are embedded in former freshwater marshes that are currently exposed to saltwater intrusion and mangrove encroachment associated with accelerating sea-level rise. In this study we resurveyed tree composition and determined environmental conditions in tree islands of the coastal Florida Everglades that had been examined two decades earlier. We asked whether tree islands in this coastal transition zone were differentiated geomorphologically as well as compositionally, and whether favorable geomorphology enabled coastal forest type(s) to maintain their compositional integrity against rising seas. Patterns of variation in geomorphology and soils among forest types were evident, but were dwarfed by differences between forest and adjacent wetlands. Tree island surfaces were elevated by 12–44 cm, and 210Pb analyses indicated that their current rates of vertical accretion were more rapid than those of surrounding ecosystems. Tree island soils were deeper and more phosphorus-rich than in the adjoining matrix. Salinity decreased interiorward in both tree island and marsh, but porewater was fresher in forest than marsh in Mixed Swamp Forest, midway along the coastal gradient where tropical hardwoods were most abundant. Little decrease in the abundance of tropical hardwood species nor increase in halophytes was observed during the study period. Our data suggest that geomorphological differences between organic tree island and marl marsh, perhaps driven by groundwater upwelling through more transmissive tree island soils, contributed to the forests’ compositional stability, though this stasis may be short-lived despite management efforts.

High-resolution satellite imaging represents a potentially effective technique to monitor cyclone-caused environmental damage and recovery over large areas at a high spatial scale. This study utilized a 10-m resolution Sentinel satellite image series to document vegetation changes in a portion of the Florida Keys, USA, over which the core of Category 4 Hurricane Irma passed on 10 September 2017. A previously assembled field survey was used to establish land-cover patterns in the satellite data, and concurrent field measurements verified post-hurricane changes. Normalized difference vegetation index (NDVI) was utilized as a tracer for pre-storm baseline patterns and through 19 post-storm months. NDVI patterns show that the severity of vegetation damage varied appreciably across the area, with the least damage on islands in the western sector of the hurricane’s eye and around its center, and greatest damage on islands just east of the eye. The data reveal that for 2.5 months after the storm, multiple inland vegetation classes showed substantial early regrowth. However, mangrove forests were more negatively affected. The storm caused extensive mortality of black mangrove (Avicennia germinans) and red mangrove (Rhizophora mangle), corresponding to more than 40% of the total mangrove area on some islands. The full extent of mangrove die-off was not immediately evident, and increased progressively through the first few months after the storm. In addition to demonstrating the utility of high-resolution satellite image series for post-hurricane environmental assessment, this study reveals high-resolution links between vegetation types, their location within the cyclone, and the extent of post-storm recovery.

Animals and plants on low elevation oceanic islands often rely on a thin lens of fresh groundwater and this lens is vulnerable to seawater contamination from storm surge. Documentation of the impact of the storm surge on the freshwater lens and its subsequent recovery is limited. In September 2017, Hurricane Irma made landfall in the Florida Keys as a category 4 storm with storm surge heights in excess of 2 m. This study used Electrical Resistivity Tomography (ERT) to investigate the effect of the storm surge on the freshwater lens of Big Pine Key, FL. The study compared ERT images along three profiles ranging between 220 and 280 m length collected in 2011 with post storm data collected about 3 to 4 months (November 2017/January 2018) and eight (May 2018) months after Irma. The post storm data documented that the storm surge impacted the freshwater lens on all three profiles with low resistivity (i.e., high salinity) zones in the upper 2 m of the groundwater. The increase in salinity was most pronounced in the lower elevations of the profiles. The May 2018 data were collected immediately after 2 weeks of intense precipitation. These data showed 40% recovery of the freshwater lens, most pronounced in the lower elevation of the profiles. This suggests that both the impact of storm surge and the freshwater recovery due to precipitation are most pronounced in low elevation regions where both saline and freshwater can collect at the surface.

Hurricanes are a frequent disturbance in the western Atlantic impacting coastal forest structure and persistence. This study addressed the hypothesis that periodic hurricane-associated winds and storm surges can interact with sea-level rise to cause the demise of coastal pine forests, based on the response of the Florida Keys’ last extensive tract of slash pine (Pinus elliottii var. densa) following Hurricane Irma (September 2017). Irma’s winds reached Category 4 strength in the study area on Big Pine Key, and storm surge flooded the island’s low limestone surface with salt water for the third time in 20 years, including Hurricanes Georges in 1998 and Wilma in 2005. Total mortality was 32% and was concentrated in the largest trees. Broken and uprooted trees that died immediately were distributed randomly across the elevation gradient, but trees without major stem damage that succumbed later occupied lower elevations. The extensive salt water flooding at low elevations was likely an agent of the mortality of slash pine, a fresh water–dependent species. Mortality due to Hurricane Irma contributed to a 1998–2018 decline in pine tree density and biomass of 74% and 80%, respectively. These dynamics were characterized by pine recruitment that was minimal in comparison with the three hurricane-driven mortality episodes. The data suggest that the 6 cm sea-level rise over the period exacerbated storm surge mortality by ponding salt water over more of the land surface, and the resulting scarcity of mature trees contributed to recruitment failure. In effect, the population declined at each disturbance, sea-level rise magnified these losses, and the local resilience of the population, i.e., its capacity to recover, was exceeded.

Critical resources for birds nesting in cities can support populations in spite of the challenges imposed by urbanization, and the identification of such resources can shed light on how species are able to adapt to novel environments. In the case of woodpeckers, these resources also support the conservation of secondary cavity-nesters. Woodpecker nesting has been well-studied in temperate regions, including within urban areas, but in subtropical and tropical regions, less is known. Here we ask what types of trees and what habitats woodpeckers use most, and which species of woodpeckers create the most nest cavities. We recorded information from 967 woodpecker nest trees in the region surrounding Miami, Florida, USA, which contained 1864 nest cavities excavated by four woodpecker species. Palm trees were used more than all other tree categories, and royal palms (Roystonea regia) were the most-used species overall. Woodpeckers preferentially excavated palm snags in every habitat where they were available and three of the four woodpecker species used palms snags over all other categories of trees. Red-bellied Woodpeckers (Melanerpes carolinus) were the most prolific cavity excavators, creating 78.1% of holes. Remnant patches of two native forest types contained the highest densities of woodpecker nest trees. We found a higher density of nest trees in moderately-developed suburban areas than either rural, agricultural areas or in the highly-developed urban core. We consider how these results can inform conservation efforts in the developing tropics, and especially within similar urbanizing environments in the nearby Caribbean.

As sea level rises in low-lying coastal islands, salt-tolerant (halophytic) coastal vegetation communities may be able to migrate inland, replacing the freshwater vegetation that is unable to tolerate salt stress. The pace of such shifts may be accelerated by a self-reinforcing feedback between the halophytic vegetation and salinity, as well as by frequent and intensified salinity pulses associated with the increasing impact of storm surges as a consequence of sea-level rise. We used a modification of a previously published spatially explicit individual-based model that simulates impacts on upland freshwater hammock communities from sea-level rise and storm surge to predict the interaction between three coastal communities: mangroves, hammocks, and pinelands. The model simulation predicted two qualitative characteristics regarding the interaction between these three different coastal communities: (1) mangroves and hammock communities tend to have ground water with high salinities, while at the same time pineland ground water salinity is low, and (2) pineland located at lower elevation relative to adjacent hammock will be negatively influenced by higher ground water salinities in hammocks, as it flows toward the lower elevation pineland. We tested these predictions using foliar δ13C of Conocarpus erectus collected from Big Pine Key as a proxy for ground water salinity. Measurements of ground water salinity via this proxy confirmed the two predictions of the model. Our approach provides an approximation of the impacts of sea-level rise on terrestrial vegetation communities, including threatened pineland communities, and can be used as a tool for management decisions.

Digital elevation models (DEMs) derived from remote sensing data provide a valuable and consistent data source for mapping coastal flooding at local and global scales. Mapping of flood risk requires quantification of the error in DEM elevations and its effect on delineation of flood zones. The ASTER, SRTM, ALOS, and TanDEM-X (TDX) DEMs for the island of Hispaniola were examined by comparing them with GPS and LiDAR measurements. The comparisons were based on a series of error measures including root mean square error (RMSE) and absolute error at 90% quantile (LE90). When compared with >2000 GPS measurements with elevations below 7 m, RMSE and LE90 values for ASTER, SRTM, ALOS, TDX DEMs were 8.44 and 14.29, 3.82 and 5.85, 2.08 and 3.64, and 1.74 and 3.20 m, respectively. In contrast, RMSE and LE90 values for the same DEMs were 4.24 and 6.70, 4.81 and 7.16, 4.91 and 6.82, and 2.27 and 3.66 m when compared to DEMs from 150 km2 LiDAR data, which included elevations as high as 20 m. The expanded area with LiDAR coverage included additional types of land surface, resulting in differences in error measures. Comparison of RMSEs indicated that the filtering of TDX DEMs using four methods improved the accuracy of the estimates of ground elevation by 20–43%. DTMs generated by interpolating the ground pixels from a progressive morphological filter, using an empirical Bayesian kriging method, produced an RMSE of 1.06 m and LE90 of 1.73 m when compared to GPS measurements, and an RMSE of 1.30 m and LE90 of 2.02 m when compared to LiDAR data. Differences in inundation areas based on TDX and LiDAR DTMs were between −13% and −4% for scenarios of 3, 5, 10, and 15 m water level rise, a much narrower range than inundation differences between ASTER, SRTM, ALOS and LiDAR. The TDX DEMs deliver high resolution global DEMs with unprecedented elevation accuracy, hence, it is recommended for mapping coastal flood risk zones on a global scale, as well as at a local scale in developing countries where data with higher accuracy are unavailable.

In response to warming winter air temperatures, freeze-sensitive mangrove forests are expected to expand at the expense of freeze-tolerant salt marshes. To better anticipate and prepare for mangrove range expansion, there is a need to advance understanding of the modulating role of microclimate. Here, we synthesized hypotheses regarding the effects of microclimatic variation on temperature gradients and mangrove freeze damage. Temperature data from the literature and from temperature loggers were used to quantify ecologically relevant temperature gradients. Then, literature-derived mangrove freeze damage data were used to quantify the ecological effects of these temperature gradients. Six microclimatic factors are described that produce air temperature gradients that modulate mangrove responses to winter temperature extremes: (1) distance from the ocean; (2) distance from wind buffers; (3) mangrove canopy cover; (4) height above the soil surface; (5) local slope concavity; and (6) tidal inundation. Variation in these factors produces local temperature differences that range from 2 to 14 °C, with concomitant effects on horizontal and vertical patterns of biological damage from freezing. Collectively, our results elucidate the influence of microclimate on spatial patterns of biological damage and mortality due to winter temperature extremes. As mangrove ranges expand in response to climate change, we anticipate that microclimatic variation will produce adverse environments where mangrove expansion is prohibited as well as expansion hot spots where mangroves are protected. Subsequent expansion into newly available habitat will occur from protection zones, and microclimatic gradients may even produce positive feedback cycles that ultimately accelerate the rate of range expansion in response to warming.

Mangroves can store more sediment organic carbon (SOC) than freshwater and salt marshes. Understanding how mangroves have responded to historical sea-level rise (SLR) is fundamental to assessing their resilience and capacity to store carbon as SLR accelerates. We quantified landscape-level temporal and spatial trends in historical coastal wetland sediment accumulation and associated SOC content (i.e., storage) along coastal-to-inland gradients in Southeast Florida. The observed trends were transgressive and attributed to the historical rise in sea level. Our results indicate an overall significant increase in the SOC content of the historic wetland sediment succession caused by the vertical accumulation and landward migration of carbon-rich mangrove-dominated plant communities (mean = 0.08 g cm−3) into and over carbon-poor wet prairie plant communities (mean = 0.02 g cm−3). The observed historical increase in SOC is predicted to diminish over time as the difference between rates of SLR and vertical sediment accumulation increases and because the landward migration of mangrove-dominated plant communities is now obstructed by a shore-parallel flood-control levee. These results are likely to unfold in other low-latitude coastal wetlands where they are sandwiched between rising seas and an urbanized landscape.

Multiple invasive cavity-nesting bird species can be present in a nest web, the network linking birds using cavities. We investigated the nest preferences and breeding phenologies of the cavity-nesting guild in the region surrounding Miami, Florida, USA, where invasive starlings, mynas, and parrots potentially usurp cavities from native woodpeckers and secondary cavity-nesters. We asked if the timing of reproduction determines which invasive species will usurp cavities from native birds with similar nest preferences. Nest usurpations between European Starlings (Sturnus vulgaris) and the woodpecker species present in Miami is well documented, but we predicted that a recently arrived sturnid species and introduced psittacids would also usurp nests. European Starlings had the largest breeding population of any species in our nest web, breeding during the peak of nesting season, and usurped the largest number of active nest cavities. We found that a small population of Common Mynas (Acridotheres tristis) usurped nests, sharing the peak-season nesting period with starlings and native woodpeckers. Parrots bred later than we expected, avoiding nest-site overlap with similarly large native birds that use cavities with similar characteristics. Parrots did not usurp any active nest cavities from native birds. Our results demonstrate how to use analysis of cavity characteristics and reproductive timing to evaluate threats to a cavity nest web posed by multiple invasive species. Common Myna currently usurp few nests; if they increase greatly in population, they could pose a problem for native cavity-nesters.

In pioneering works of Meyer and of McMullen in the early 1970s, the set of Minkowski summands of a polytope was shown to be a polyhedral cone called the type cone. Explicit computations of type cones are in general intractable. Nevertheless, we show that the type cone of the product of simplices is the cone over a simplex. This remarkably simple result derives from insights about rainbow point configurations and the work of McMullen., Comment: 12 pages, 4 figures. Incorporated referee suggestions, minor edits throughout. This version focuses more on type cones of products of simplices than the previous version. Introduction has been partially rewritten to reflect this change. To appear in the Bulletin of the London Mathematical Society

The hardwood forests of south Florida, commonly referred to as hammocks, persist as well‐drained patches of broadleaf forest, embedded in a matrix of brackish water swamp, freshwater marsh, or pineland. Little is known about the patterns of community assembly of these subtropical forest communities in the landscape mosaic of south Florida. We used a functional trait approach to understand the composition of these communities and their responses to environmental variation across four areas of south Florida: the pine rocklands and freshwater marshes in Everglades National Park, and the lower and upper Florida Keys, where the hammocks are surrounded by halophytic swamp communities. These sites represent an environmental gradient from less‐productive, more xeric sites in the lower Florida Keys, to more‐productive, wetter sites in the Everglades marshes. We examined the patterns of trait variation at three levels (individual, population, and community) to examine the underlying processes driving assembly in these hammock communities. To understand processes governing community composition in each site, we used methods that partition variance in six traits (maximum tree height, specific leaf area, wood specific gravity, leaf nitrogen, leaf phosphorus, and leaf stable carbon isotope ratios) into internal and external filtering components. Community‐weighted mean trait values for three traits (specific leaf area, height, and leaf phosphorus) increased significantly from dry, less‐productive coastal sites in the Florida Keys to the moist, more‐productive areas on the mainland, while wood specific gravity and leaf δ13C showed the opposite pattern. For one or more traits per site, standardized effect sizes differed significantly from null expectation. Processes such as competition for resources (e.g., water, nutrients, light) and species sorting across microhabitats (i.e., within site) operate to increase local functional trait variation within communities and among species across sites. External filtering on individuals for height and leaf phosphorus differed significantly from null expectations across sites, while external filtering on species was only observed for specific leaf area, maximum tree height, and leaf phosphorus. These results are consistent with strong environmental filtering across the region, among local communities differing in freshwater accessibility or that occupy different positions along strong edaphic gradients. Our results confirm the importance of intraspecific variation among species and reflect a high degree of trait plasticity across the environmental gradient.

Plant communities arranged along a gradient are a product of underlying physico-chemical drivers that vary on both spatial and temporal scales. Spatial variation in the underlying drivers along the gradient usually results in the formation of boundaries between adjacent plant communities. However, the structure and composition of these communities may change over time resulting in boundary shifts. In the Everglades, tree islands are complex ecosystems, where plant communities are arranged along hydrologic and soil nutrient gradients. In these islands, temporal changes in hydrologic regime often result in a spatial shift in community composition along the gradient and determine the trajectory of community succession. We examined the interaction between hydrology and vegetation over a 12-year period in three southern Everglades tree islands. We hypothesized that drier conditions in recent decades would result in an increase in the dominance of flood in-tolerant woody plants over herbaceous and flood-tolerant woody species, ultimately causing a shift in the boundaries between plant communities. The boundary between adjacent communities varied from sharp, clearly defined peaks of Bray-Curtis dissimilarity to more gradual, diffuse transition zones. In the head portion of tree island, there was little change in vegetation composition. However, in the tail portion of the islands, the relative abundance of flood-tolerant species declined, while that of moderately flood-tolerant species increased over the study period. In these islands, the effects of relatively dry conditions in recent decades resulted in small shifts in the boundaries among communities. These results suggest that tree islands are dynamic successional communities whose expansion or contraction over time depends on the strength and duration of changes in hydrologic conditions.

Tree species in coastal forests may exhibit specialization or plasticity in coping with drought through changes in their stomatal morphology or activity, allowing for a balance between gas exchange and water loss in a periodically stressful environment. To examine these responses, we sought to answer two primary research questions: a) how is variation in B. simaruba’s stomatal traits partitioned across hierarchical levels, i.e., site, tree, and leaf; and b) is variation in stomatal traits an integrated response to physiological stress expressed across the habitat gradient of Florida Keys forests? At eight sites distributed throughout the Keys, five leaves were collected from three mature trees for stomatal analysis. Leaf carbon stable isotope ratio (δ13C) was determined to infer the changes in water use efficiency caused by physiological stress experienced by each tree. The results showed that substantial proportions of the total variance in three traits (stomatal density, stomatal size, and δ13C) were observed at all levels, suggesting that processes operating at each scale are important in determining trait values. A significant negative correlation between stomatal density and size across scales was observed. Path model analysis showed that environmental variables, distance to ground water and ground water salinity, affect leaf δ13C indirectly, via its effects on stomatal traits, not directly to leaf δ13C. Therefore, the combination of small and densely distributed stomata seems to represent a strategy that allows B. simaruba to conserve water under conditions of physiological drought induced by either higher ground water salinity or flooding stress at very low elevation.

The Everglades is a low-gradient floodplain predominantly on organic soil that undergoes seasonally pulsing sheetflow through a network of deepwater sloughs separated by slightly higher elevation ridges. The seasonally pulsing flow permitted the coexistence of ridge and slough vegetation, including the persistence of productive, well-connected sloughs that seasonally concentrated prey and supported wading bird nesting success. Here we review factors contributing to the origin and to degradation of the ridge and slough ecosystem in an attempt to answer “How much flow is needed to restore functionality”? A key restoration objective is to increase sheetflow lost during the past century to reestablish interactions between flow, water depth, vegetation production and decomposition, and transport of flocculent organic sediment that build and maintain ridge and slough distinctions. Our review finds broad agreement that perturbations of water level depth and its fluctuations were primary in the degradation of landscape functions, with critical contributions from perturbed water quality, and flow velocity and direction. Whereas water levels are expected to be improved on average across a range of restoration scenarios that replace between 79 and 91% of predrainage flows, the diminished microtopography substantially decreases the probability of timely improvements in some areas whereas others that retain microtopographic differences are poised for restoration benefits. New advances in predicting restoration outcomes are coming from biophysical modeling of ridge–slough dynamics, system-wide measurements of landscape functionality, and large-scale flow restoration experiments, including active management techniques to kick-start slough regeneration.

Separating the effects of anthropogenic changes in freshwater delivery from that of sea level rise on the rate of salt water encroachment in the low relief Southeast Saline Everglades is important for understanding how the Anthropocene Marine Transgression might be best managed. We use stratigraphic and paleoecologic methods to calculate rates of salt water encroachment and biogenic sediment accumulation in the Southeast Saline Everglades. Our results suggest that sea level rise during the last century was accompanied by salt water encroachment, which is ultimately controlled by the elevation of high tide and varied by a factor of 14.8 in the five watersheds studied. These differences are attributed primarily to differences in freshwater delivery. The delivery of freshwater mitigated salt water encroachment in only one of the five watersheds. This difference is attributed to sufficient freshwater delivery to maintain a plant community with more rapid rate of sediment accumulation than other sites. Under conditions of diminishing freshwater availability and increasing rate of sea level rise, our data suggest that little can be done at a scale large enough to prevent loss of the Southeast Saline Everglades within the next 50–200 years.

As an outcome of natural selection, animals are probably adapted to select territories economically by maximizing benefits and minimizing costs of territory ownership. Theory and empirical precedent indicate that a primary benefit of many territories is exclusive access to food resources, and primary costs of defending and using space are associated with competition, travel and mortality risk. A recently developed mechanistic model for economical territory selection provided numerous empirically testable predictions. We tested these predictions using location data from grey wolves ( Canis lupus ) in Montana, USA. As predicted, territories were smaller in areas with greater densities of prey, competitors and low-use roads, and for groups of greater size. Territory size increased before decreasing curvilinearly with greater terrain ruggedness and harvest mortalities. Our study provides evidence for the economical selection of territories as a causal mechanism underlying ecological patterns observed in a cooperative carnivore. Results demonstrate how a wide range of environmental and social conditions will influence economical behaviour and resulting space use. We expect similar responses would be observed in numerous territorial species. A mechanistic approach enables understanding how and why animals select particular territories. This knowledge can be used to enhance conservation efforts and more successfully predict effects of conservation actions.

Transpiration-driven ion accumulation in soil has been invoked as a biological and physical feedback mechanism in wetlands that governs topographic differences by regulating soil accretion—with greater transpiration, ion accumulation and soil accretion occurring on tree islands as compared to the surrounding marsh. The strength of this mechanism is hypothesized to be controlled by the ratio of evapotranspiration (ET) to precipitation (P), where under greater ET to P conditions soil accretion may move from organic to mineral in nature. We tested the existence of this mechanism on tree islands in a subtropical wetland, determined if it supports mineral soil formation, and assessed its control on the development of nutrient resource contrasts (tree islands–marsh). To test our hypotheses, biannual measurements of groundwater, surface water and aboveground biomass were made from 2007 to 2012. Water samples were analyzed for water isotopes, concentrations of major ions, and total and dissolved nutrients on constructed tree islands. We found that tree transpiration led to the advective movement of water and associated ions toward the center of the tree islands, supporting CaCO3 precipitation. CaCO3 accretion on the tree islands was estimated at roughly 1 mm per decade, and represented 5 % of the total soil accretion since the islands’ planting. We also observed depletion in groundwater nutrient concentrations as tree biomass accumulated, indicative of tight nutrient cycling. This work provides direct evidence that trees can act as powerful geomorphic agents in wetland systems, forming mineral soils that support landscape heterogeneity on time scales of centuries to millennia.

Canopy gaps create a temporary spatial heterogeneity, often allowing pioneer species to establish and grow in mature forests. In this study, we asked whether the above model holds for tropical dry forests in the Florida Keys. Six hundred and forty-eight canopy gaps in an extensive Key Largo forest were identified with a LiDAR digital canopy model. The structure and composition of juvenile trees were examined in 45 selected gaps in three stands of known age, and weighted averaging calibration and regression were applied to the data to determine the successional age optimum for each tree species, and the inferred age for each gap based on its sapling composition. Less than 1% of the forest area was recorded as canopy gaps in the LiDAR model. The inferred stand ages were about 70 y greater in canopy gaps in young forest than in the surrounding, unimpacted forest. This suggested that gap formation advanced succession rather than reversing or resetting it. The apparent lack of recruitment by early-successional species may be due to the small size of canopy gaps in this forest, and the minimal contrast between gap and understorey environments; light and water conditions in the small gaps may favour late-successional rather than pioneer species. Establishment of pioneer species may not take place without intense, large-scale disturbances such as fires and hurricanes that remove the entire canopy and consume or erode soils.

Differential distribution of nutrients within an ecosystem can offer insight of ecological and physical processes that are otherwise unclear. This study was conducted to determine if enrichment of phosphorus (P) in tree island soils of the Florida Everglades can be explained by bird guano deposition. Concentrations of total carbon, nitrogen (N), and P, and N stable isotope ratio (δ(15)N) were determined on soil samples from 46 tree islands. Total elemental concentrations and δ(15)N were determined on wading bird guano. Sequential chemical extraction of P pools was also performed on guano. Guano contained between 53.1 and 123.7 g-N kg(-1) and 20.7 and 56.7 g-P kg(-1). Most of the P present in guano was extractable by HCl, which ranged from 82 to 97% of the total P. Total P of tree islands classified as having low or high P soils averaged 0.71 and 40.6 g kg(-1), respectively. Tree island soil with high total P concentration was found to have a similar δ(15)N signature and total P concentration as bird guano. Phosphorus concentrations and δ(15)N were positively correlated in tree island soils (r = 0.83, p0.0001). Potential input of guano with elevated concentrations of N and P, and (15)N enriched N, relative to other sources suggests that guano deposition in tree island soils is a mechanism contributing to this pattern.

Increases in the rate of sea level rise are likely to result in changes to disturbance-adapted coastal forests and associated freshwater resources over the next several decades. In this study, we investigated how the press disturbance of two decades of sea level rise altered island hydrology and interacted with pulse disturbances (frequent hurricane impacts) to alter coastal forest composition and structure. The research was conducted on two low-elevation islands located within the lower Florida Keys: Big Pine and Upper Sugarloaf Keys. Groundwater salinity and vegetation structure and composition were sampled in the early 1990s prior to impact from two hurricanes – Hurricanes Georges (1998) and Wilma (2005) – and again in 2012/2013 in permanent plots inside and outside the boundaries of the islands’ freshwater lenses. Using linear mixed effects modeling, we examined whether groundwater salinity varied over time among locations, and investigated whether this variation was reflected in changes in forest structure and composition in three height strata. The results of this analysis revealed that groundwater salinity underlying plots outside the freshwater lens increased over the two decades, while salinity of groundwater at plots inside the freshwater lens remained stable. The greatest shift in composition occurred in the understory strata along a gradient of increasing salinity, and plots located outside the freshwater lens gained species typical of tidally-influenced buttonwood forest and lost glycophytic species. Viewed against the background of recurring hurricane impacts, these findings suggest that sea level rise is currently altering both groundwater resources and the composition of coastal forests in the Florida Keys. Similar dynamics should be observed in low-lying coastal forests within ocean basins subject to increased tropical cyclone activity. Management of these island coastal forests must now consider the continually shifting nature of the resource in light of acceleration in sea level rise.

© 2018 The Authors. Journal of Biogeography Published by John Wiley & Sons Ltd Aim: Seasonally dry tropical forest (SDTF) of the Caribbean Islands (primarily West Indies) is floristically distinct from Neotropical SDTF in Central and South America. We evaluate whether tree species composition was associated with climatic gradients or geographical distance. Turnover (dissimilarity) in species composition of different islands or among more distant sites would suggest communities structured by speciation and dispersal limitations. A nested pattern would be consistent with a steep resource gradient. Correlation of species composition with climatic variation would suggest communities structured by broad-scale environmental filtering. Location: The West Indies (The Bahamas, Cuba, Hispaniola, Jamaica, Puerto Rico, US Virgin Islands, Guadeloupe, Martinique, St. Lucia), Providencia (Colombia), south Florida (USA) and Florida Keys (USA). Taxon: Seed plants—woody taxa (primarily trees). Methods: We compiled 572 plots from 23 surveys conducted between 1969 and 2016. Hierarchical clustering of species in plots, and indicator species analysis for the resulting groups of sites, identified geographical patterns of turnover in species composition. Nonparametric analysis of variance, applied to principal components of bioclimatic variables, determined the degree of covariation in climate with location. Nestedness versus turnover in species composition was evaluated using beta diversity partitioning. Generalized dissimilarity modelling partitioned the effect of climate versus geographical distance on species composition. Results: Despite a set of commonly occurring species, SDTF tree community composition was distinct among islands and was characterized by spatial turnover on climatic gradients that covaried with geographical gradients. Greater Antillean islands were characterized by endemic indicator species. Northern subtropical areas supported distinct, rather than nested, SDTF communities in spite of low levels of endemism. Main conclusions: The SDTF species composition was correlated with climatic variation. SDTF on large Greater Antillean islands (Hispaniola, Jamaica and Cuba) was characterized by endemic species, consistent with their geological history and the biogeography of plant lineages. These results suggest that both environmental filtering and speciation shape Caribbean SDTF tree communities.

Zero forcing is a process on a graph that colors vertices blue by starting with some of the vertices blue and applying a color change rule. Throttling minimizes the sum of the size of the initial blue vertex set and the number of the time steps needed to color the graph. We study throttling for positive semidefinite zero forcing. We establish a tight lower bound on the positive semidefinite throttling number as a function of the order, maximum degree, and positive semidefinite zero forcing number of the graph, and determine the positive semidefinite throttling numbers of paths, cycles, and full binary trees. We characterize the graphs that have extreme positive semidefinite throttling numbers., Comment: 20 pages, 7 figures, in press, Discrete Appl. Math

Hurricane-caused tree mortality in tropical dry forests occurs predominantly in early successional species. Consequently, hurricanes may accelerate succession in these forests. Forest regeneration, however, must be measured over an extended posthurricane time period to demonstrate this pattern. In this study, we recorded tree seedlings in 19 Florida Keys forests during May–August 1995, 3 years after Hurricane Andrew. For these forests—spanning a chronosequence from 14 to over 100 years since the most recent clearing—we used weighted averaging regression on relative abundances of pre-hurricane trees to calculate a successional age optimum for each species; and used weighted averaging calibration to calculate inferred successional ages for stands based on pre-hurricane trees and on posthurricane seedlings. To test the hypothesis that successional stage of seedlings exceeded successional stage of pre-hurricane trees, we compared inferred stand ages based on posthurricane seedlings with those based on pre-hurricane trees. Across the study area, inferred stand ages based on posthurricane seedlings were greater than those based on pre-hurricane trees (P

Tree islands are habitat for wading birds and a characteristic landscape feature in the Everglades. A total of 93 surface soil and 3 soil core samples were collected from 7 degraded/ghost and 34 live tree islands. The mean Hg concentration in surface soils of ghost tree islands was low and similar to marsh soil. For live tree islands, Hg concentrations in the surface head region were considerably greater than those in mid and tail region, and marsh soils. Hg concentrations in bird guano (286 μg kg −1 ) were significantly higher than those in mammal droppings (105 μg kg −1 ) and plant leaves (53 μg kg −1 ). In addition, Hg concentrations and δ 15 N values displayed positive correlation in soils influenced by guano. During 1998–2010, estimated annual Hg deposition by guano was 148 μg m −2 yr −1 and ∼8 times the atmospheric deposition.

Transpiration-driven nutrient accumulation has been identified as a potential mechanism governing the creation and maintenance of wetland vegetation patterning. This process may contribute to the formation of nutrient-rich tree islands within the expansive oligotrophic marshes of the Everglades (Florida, United States). This study presents hydrogeochemical data indicating that tree root water uptake is a primary driver of groundwater ion accumulation across one of these islands. Sap flow, soil moisture, water level, water chemistry, and rainfall were measured to identify the relationships between climate, transpiration, and groundwater uptake by phreatophytes and to examine the effect this uptake has on groundwater chemistry and mineral formation in three woody plant communities of differing elevations. During the dry season, trees relied more on groundwater for transpiration, which led to a depressed water table and the advective movement of groundwater and dissolved ions, including phosphorus, from the surrounding marsh towards the centre of the island. Ion exclusion during root water uptake led to elevated concentrations of all major dissolved ions in the tree island groundwater compared with the adjacent marsh. Groundwater was predominately supersaturated with respect to aragonite and calcite in the lower-elevation woody communities, indicating the potential for soil formation. Elevated groundwater phosphorous concentrations detected in the highest-elevation woody community were associated with the leaching of inorganic sediments (i.e. hydroxyapatite) in the vadose zone. Understanding the complex feedback mechanisms regulating plant/groundwater/surface water interactions, nutrient dynamics, and potential soil formation is necessary to manage and restore patterned wetlands such as the Everglades. Copyright © 2013 John Wiley & Sons, Ltd.

Within the marl prairie grasslands of the Florida Everglades, USA, the combined effects of fire and flooding usually lead to very significant changes in tree island structure and composition. Depending on fire severity and post-fire hydroperiod, these effects vary spatially and temporally throughout the landscape, creating a patchy post-fire mosaic of tree islands with different successional states. Through the use of the Normalized Difference Vegetation Index (NDVI) and three predictor variables (marsh water table elevation at the time of fire, post-fire hydroperiod, and tree island size), along with logistic regression analysis, we examined the probability of tree island burning and recovering following the Mustang Corner Fire (May to June 2008) in Everglades National Park. Our data show that hydrologic conditions during and after fire, which are under varying degrees of management control, can lead to tree island contraction or loss. More specifically, the elevation of the marsh water table at the time of the fire appears to be the most important parameter determining the severity of fire in marl prairie tree islands. Furthermore, in the post-fire recovery phase, both tree island size and hydroperiod during the first year after the fire played important roles in determining the probability of tree island recovery, contraction, or loss.

Ecosystem management practices that modify the major drivers and stressors of an ecosystem often lead to changes in plant community composition. This paper exam- ines how closely the trajectory of vegetation change in seasonally-flooded wetlands tracks management-induced al- terations in hydrology and soil characteristics. We used trajectory analysis, a multivariate method designed to test hypotheses about rates and directions of community change, to examine vegetation shifts in response to changes in water management practices within the Taylor Slough basin of Everglades National Park. We summarized vegetation data by non-metric multidimensional scaling ordination, and ex- amined the time trajectory of each site along environmental vectors representing hydrology and soil phosphorus gradi- ents. In the Taylor Slough basin, vegetation change trajec- tories closely followed the hydrologic changes caused by the operation of water pumps and detention ponds adjacent to the canals. We also observed a shift in vegetation com- position along a vector of increasing soil phosphorus, which suggests the need for implementing measures to avoid P- enrichment in southern Everglades marl prairies. This study indicates that shifts in vegetation composition in response to changes in hydrologic conditions and associated parameters may be detected through trajectory analysis, thereby provid- ing feedback for adaptive management of wetland ecosystems.