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Abstract Rockland habitat in South Florida, USA, is a threatened ecosystem that has been lost, fragmented, or degraded because of urbanization or other anthropogenic disturbance. Furthermore, low‐lying islands and coastal areas are experiencing sea level rise (SLR) and an increased frequency and intensity of tidal flooding, putting rockland habitats there at increasing risk of ecological change. We evaluated changes in the extent of rockland habitat under various scenarios of future SLR, tidal flooding, and human development for two endemic state‐listed threatened species of snakes, the Rim Rock Crowned Snake (Tantilla oolitica) and the Key Ring‐necked Snake (Diadophis punctatus acricus). Both snakes are restricted to South Florida. We used recent and historical species' records to determine each species' habitat range. We then estimated the extent of future habitat loss due to SLR and continued human development, as well as degradation of the remaining habitat. We also asked whether the future potential drivers of habitat loss and degradation differ between the two species and across their habitat ranges. We predicted that saltwater intrusion could negatively affect rocklands by 2050, resulting in degradation of 80% of the existing habitat because of an anticipated 42 cm of SLR. Moreover, our model suggests short‐term stochastic events such as storm surge and high tides may increasingly saturate the root zone of rockland vegetation before complete inundation. Under the extreme scenario, we predict most of the rockland habitat used by these two species of snakes may be inundated by 2080. Under the extreme SLR scenario, current rocklands are likely to convert to more halophytic habitat (mangrove or salt marsh wetland) within 50–60 years. Under the low scenario, 31% of rockland habitat may be lost due to human development by 2030. Therefore, mitigation actions may help to conserve specialist species within rockland habitat threatened by human activities and climate change.

Abstract Tree islands, a prominent feature of wetland landscapes worldwide, are patches of forest scattered throughout a matrix of herbaceous marsh. In the Florida Everglades, their development over millennia as elevated, relatively well‐drained features above the wetland surface has made them cultural centers for indigenous people and refugia for a rich assortment of plants and animals. However, since the early years of the twentieth century, the number and area of tree islands have been roughly halved in Everglades National Park and Water Conservation Areas due to scarce or excessive water levels, leading to fires or persistent flooding, respectively. This loss has prompted a need for tree island rehabilitation or reconstruction within the ongoing state–federal partnership to bring about Everglades restoration. In this paper, we present results of a field‐scale experiment that examined the effects of flooding, planting density, and the size and proximity of neighbors on the performance of native tree species on constructed tree islands. Hypotheses derived using the stress‐gradient hypothesis as a framework were tested at the neighborhood level. Flooding reduced survival and mean tree size 7–8 years after initial planting, while planting seedlings at spacings as close as 1 m apart resulted in higher total biomass, with no significant cost in tree survival. Flood‐tolerant species increased in relative abundance during the study period along the entire hydrologic gradient, while flood‐intolerant species were able to survive only at higher elevations. Crowding effects within neighborhoods varied across the flooding gradient. Survival increased or remained stable as neighbor effects increased in high‐flooding zones, while declining sharply as crowding increased under low‐flooding conditions. Similar results were obtained for the growth of flood‐tolerant species under close spacing, with most showing an increment in growth where flooding was high. These data suggest that tree island restoration can benefit from targeted mixed‐species plantings at variable densities, as the compositional and structural heterogeneity promoted by these measures may increase adaptability and resilience to future uncertainties.

Numerous studies address changes in wetland deposition in response to saltwater encroachment driven by the accelerating rate of sea-level rise, by quantifying temporal changes recovered from a vertical sediment sequence. This is the first landscape scale study, based upon 10 core transects representing the heterogeneity of the Southeast Saline Everglades, Florida. By utilizing the known salinity preferences of molluscan assemblages, a Salinity Index was calculated for each core sequence and the recorded salinity changes identified and dated. Radiometric dating utilizing the 210Pb method provides the rate of sediment accumulation and the date of changes identified in the core. The core transects provide the basis for calculation of the rate of saltwater encroachment by comparing the date of saltwater encroachment and the distance between two cores. Thereby, temporal and spatial changes in other sediment parameters in a landscape can also be quantified, such as organic carbon. This paleo-ecological approach to rapidly changing coastal conditions can be utilized to provide scientists and land managers with a record of the past, rate of changing conditions and provide the basis for predicting the future trajectory of their site. Application of this paleo-ecological approach documented increasing rates of saltwater encroachment associated with accelerating rate of sea-level rise: an average rate of 49.1 between 1895 and 1940, 69.2 between 1940 and 1968, 73 between 1968 and 1995 and 131.1 m/yr between 1995 and 2015. Approximately 1.79 km of saltwater encroachment has occurred since 1995, with three partial reversals because of increased freshwater delivery. Associated with saltwater encroachment are changes in sediment organic carbon, decreasing area of marl production and increasing distribution of mangrove. Although the distance of saltwater encroachment is greater in Florida Bay, both changes in sediment organic carbon and mangrove distribution are much less than in Biscayne Bay coastal basins. This heterogeneity is likely the result of differences in tidal ingress efficiency. At the present rate of saltwater encroachment, the freshwater wetlands are predictably lost within a century.