Impact of Willow Invasion on Vegetation Water and Carbon Exchange in the Florida Everglades

Southern coastal willow (Salix caroliniana) is native to the Florida Everglades, commonly found on drier landforms like levees and tree islands. Shortened periods of inundation due to water management have led to the encroachment and expansion of these shrubs in sawgrass (Cladium jamaicense) marsh communities. The broadleaf willow is morphologically and physiologically different from the graminoid sedge sawgrass, with possible consequence for microhabitat conditions and ecosystem function. Willow is often assumed to have greater rates of transpiration, thereby affecting wetland water management, and may have concurrent differences in photosynthesis and carbon exchange. However, the ecophysiological impact of the willow invasion has not been quantified. We assessed differences in plant water and carbon exchange between willow and sawgrass at Blue Cypress Conservation Area, an impounded sawgrass peatland within the St. John's River Water Management District (SJRWMD). Plant transpiration and net CO2 exchange (photosynthesis and autotrophic respiration) were measured on fully expanded, non-damaged leaves of sawgrass and willow using a portable infrared gas analyzer (LI-6400XT, LI-COR, Lincoln, NE, U.S.A.). The results obtained from this study will provide a better understanding of ecophysiological changes that occur within marsh communities with shrub expansion, which will have cascading impacts on soil accretion and turnover, microclimate, and water quality Understanding the implications of willow expansion will improve landscape models of wetland water and carbon exchange as well as inform water management decisions.