Budny, Michelle L.

Purpose: This project will assess the consequences of expansion of coastal willow Salix
caroliniana in sawgrass Cladium jamaicense-dominated wetlands on plant community
composition and ecosystem water and carbon exchange. Methods: Research will be conducted at
Blue Cypress Conservation Area, an impounded sawgrass peatland within the St. John’s Water
Management District SJWMD located in Vero Beach, FL. It is part of the River Basin Project
controlled by SJWMD and the US Army Corps of Engineers, which moderates flooding, protects
water quality, and reduces the amount of freshwater diverted to the Indian River Lagoon. Plant
transpiration and CO2 exchange will be measured on fully expanded, non-damaged leaves of
sawgrass and willow using a portable infrared gas analyzer LI-6400, LI-COR, Lincoln, NE,
U.S.A.. Plant community composition in both habitats will be surveyed along with
measurements of microhabitat conditions and water quality. Results: The results obtained from
this study will provide a better understanding of physiological responses and community changes
that may occur in sawgrass habitats as a result of willow encroachment. It is anticipated that
there will be differences in transpiration rates between the two species as well as changes to
community structure and water quality. Measuring plant level physiological responses will help
improve landscape level models of water exchange as well as inform water management
decisions.

Shortened periods of inundation due to water management have led to the encroachment and expansion of Carolina willow (Salix caroliniana) in sawgrass (Cladium jamaicense) marsh communities. Morphologic and physiologic differences between sawgrass and willow have potential consequences for microhabitat conditions and ecosystem function such as a reduction in temperatures and light availability and changes in primary productivity. Since it is a woody shrub, willow is often assumed to exhibit higher rates of transpiration than non woody plants, which in turn can affect photosynthesis and carbon exchange and ultimately wetland water management. In this study willow was found to have higher rates of stomatal conductance (gs) and photosynthesis (Anet) than sawgrass. However, sawgrass had greater intrinsic water use efficiency (WUE) than willow. This suggests that willow is capable of greater gas exchange and carbon assimilation than sawgrass but requires more water. Understanding the implications of willow expansion will improve landscape models of wetland water and carbon exchange and inform water management decisions.