Pterocarpus officinalis dominated forests are a rare ecosystem, found only in fifteen locations in Puerto Rico, all of which are adjacent to the coast and at risk from sea level rise, as well as nutrient pollution, upstream hydrological modifications, and deforestation. All forests of this type that were located further inland were destroyed by agricultural development during the early decades of the 1900’s, in particular to grow sugarcane. Prior to this study, there was little information on the diversity of organisms that live in these forests. The central objective of this proposal was to examine the diversity and species composition of three Pterocarpus forests in Puerto Rico located near Humacao, Patillas, and Dorado, and to compare and contrast diversity among the three forests, and identify possible differences caused by human impacts or natural factors. The data was collected through surveys and sampling at each location. Transect surveys, plots, pitfall traps, insect traps and audio recordings were carried out to identify organisms including birds, mammals, amphibians and reptiles, insects, mollusks, invertebrates, plants and fungi. The Dorado Pterocarpus forest is the most rich and diverse in terms of organisms and has the highest amount of native and endemic species, while the Humacao Pterocarpus forest is the least rich and diverse. Yet conversely, the Dorado forest is the smallest forest, covering only 2.4 ha, while Humacao is the largest, with an area of 150 ha that comprises 63% of the total Pterocarpus coverage in Puerto Rico. The most obvious factor influencing richness and diversity among the forests is the adjacent land cover and history of the sites. Inflow and water sources may also be a factor that alters richness and diversity. This knowledge will assist in the appropriate management of this rare resource in the context of ongoing sea level rise, climate change, nutrient pollution, upstream hydrological modifications, and deforestation. Coastal managers need this information to manage and protect these valuable and rare ecosystems.

Global climate change threatens the survival of microtidal wetlands by altering fundamental hydrological aspects such as precipitation patterns and tidal exchange. The combination of these stressors results in increased flooding period and soil salinity in coastal wetlands. In this study, we combined the use of detailed hydrological measurements (wetland water level and salinity), LIDAR elevation models, and water stable isotopes tracers (δD, δ18O) to study the balance between freshwater and saltwater inputs on two microtidal wetlands: a saltmarsh in Matagorda, Texas and a freshwater-forested wetland in Humacao, Puerto Rico. In Matagorda, Texas, we described the process of connectivity between different hydrologic units (isolated and connected ponds) within the saltmarsh. Pond connectivity only occurred when water levels in major water bodies adjacent to our study site reached a threshold elevation of 0.39 m. Connections events were correlated to rainfall and— to a lesser extent— wind speed and direction. We conclude that connectivity within the saltmarsh is driven by the combined effect of tidal influence and rainfall inputs, factors that will be altered by sea level rise and climate change-related changes in long term weather patterns. In Humacao, Puerto Rico, we gathered a detailed dataset of changes in salinity and water level in a freshwater forested wetland dominated by the endangered salt intolerant species Pterocarpus officinalis. In addition, we studied tree water use and identified important water sources to the wetland using stable isotope tracers. Firstly, we provide evidence that recent hydrological alterations have effectively transformed the system from mostly freshwater, to a saltwater wedge estuary. Salinity inputs travel via a tidal creek channel that allows the progression of a saltwater wedge to the inland parts of the forest. Our results suggest that inland progression of the saltwater wedge is influenced by amplitude of tidal exchange in the middle portions of the tidal creek and by extended dry periods in the headmost part of the tidal creek. Isotope data showed that surface standing water was influenced by tidal water sources during the dry season, although the spatial extent of this influence was constrained to areas of the forest that had been previously deforested. The isotopic content of groundwater samples taken at increasing distances from the tidal creek revealed that— although surface waters are dominated by freshwater inputs (rainfall and runoff) during the wet season— the influence of tidal water sources at soil depths greater than 60 cm persists throughout the year. Nonetheless, isotopic content of Pterocapus officinalis stem water samples suggest that tree water uptake is constrained to very shallow, unsaturated parts of the soil. We conclude from both case studies that the long term vulnerability of microtidal wetlands to climate change is determined by the interaction of increased annual variability of freshwater inputs along with a steady increase in mean sea levels, and aggravated by extreme climatic events.