Water-use Comparison of the Invasive Tree Species, Melaleuca Quinquenervia, and two Native Tree Species,Taxodium Distichum and Pinus Elliottii, in Southwest Florida

Melaleuca (Melaleuca quinquenervia), an invasive tree species in southern Florida, is generally thought to have higher transpiration rates than the native vegetation, however little empirical data is available to support this claim. In this study, thermal dissipation probes were used to measure transpiration rates of the three species growing in a hydric ecotone in southwest Florida. Transpiration rates of melaleuca, slash pine (Pinus elliottii), and bald cypress (Taxodium distichum) were compared to assess seasonal variability between the wet and dry seasons. Individually trees of both bald cypress and slash pine showed significantly higher water fluxes than melaleuca (p<0.05). However, when individual tree fluxes were scaled to the ecosystem-level, melaleuca contributed 21% of the water flux and bald cypress contributed 72% during the wet season. Melaleuca's increased contribution at the landscape-level results from higher tree densities at our study site. Following leaf senescence in the early dry season, bald cypress continues to be a significant water user at the landscape level. With higher atmospheric demands for water, bald cypress was the least conservative of the three species with respect to water use, whereas on days with low atmospheric demands for water the three species function similarly. These results do not support the hypothesis that melaleuca uses more water than the native Florida tree species, however, they suggest the density of melaleuca at the landscape-scale is important in our understanding of its role in the hydrologic cycle.