RECOVER MAP 3.1.3.6 Landscape Pattern - Ridge, Slough, and Tree Island function in relation to marsh hydrology

This project will support two existing MAP projects: 1) Tree Islands in Everglades National Park (ENP) - Big Cypress and 2) Tree Island Stage Duration and the measurement of water depth on tree islands located in WCA 3A and 3B. While these projects have similar broad objectives, some of the specific monitoring design and constituents differ. Tree island elevations and species composition were measured on over 200 islands in WCA 3, while community dynamics, hydrology, soil moisture, and transpiration and growth rates of the dominant trees are monitored on tree islands located within ENP. The ENP monitoring program was based on work originally funded by the ENP in 2005. Ross and Oberbauer (2006) have shown large seasonal differences between dry and wet season transpiration rates in an island located in the eastern prairies of ENP. However, no seasonal differences were observed in the islands located in Shark Slough where the dry season water levels remained above the marsh surface. These results have implications for the management of these systems, since it appears that extended dry-downs during the November – May dry season may cause significant declines in tree island productivity. These changes in productivity, in turn, may alter the role tree islands play in nutrient cycles in the Everglades marshes. The role of tree islands in marsh nutrient cycles has been the subject of recent journal articles (Ross et al. 2006, Wetzel et al. 2005), and in the last year RECOVER has sponsored several discussions dedicated to the development of tree island conceptual models and performance measures (e.g. GEER 2008). The WCA 3 monitoring effort has begun to add many of the physiological measurements to their monitoring program, but is currently lacking the funding necessary to fully implement the effort. This work will place all the existing MAP projects within a common framework that links tree island productivity with nutrient cycles and hydrologic conditions in the marsh. The results are expected to provide information useful for the development of cost-effective, long-term monitoring tools for the MAP.
The overall objective of the study is to test the transpiration model presented by Ross et al. (2006 and Wetzel et al. (2005), which states that high transpiration is the driving force for nutrient accumulation of tree islands (Fig 1). According to this model, slough tree islands can maintain high transpiration rates during the dry season using standing marsh water around the island or groundwater, while prairie tree islands will have low transpiration rate during dry season due to low water availability. Thus, the difference in hydroperiod between slough and prairie tree islands will result in differential nutrient accumulation rates and suggests that slough tree islands can accumulate more nutrients than prairie tree islands.

The specific objectives of this study are 1) to test whether there is a decrease in transpiration from wet to dry season in prairie tree islands but not in slough tree islands, 2) to test whether the above transpiration shift is reflected in the foliar carbon isotope ratios and 3) to test whether prairie tree islands showing the decrease from wet to dry season transpiration have lower foliar nutrient concentrations compared to slough tree islands. The objective is to use Granier probes to measure sap flux rates as a proxy for transpiration, foliar carbon and nitrogen isotope analysis as well foliar phosphorus and nitrogen concentrations to answer the above questions. The results of this project will be submitted to a peer reviewed journal. The results of this research will link transpiration with nutrient accumulation and will provide guidelines to tree island models. In addition, the foliar isotopic analysis, if consistent with the above hypotheses, will provide a measure of tree island nutrient stability and may be suitable for use as a MAP monitoring tool.