Shrubs Accelerate Wetland Water Loss
As shrubs encroach, their leaves drive the “wet” out of wetlands.
Water is a defining characteristic of wetlands and a key influence on biodiversity and biogeochemistry. Unfortunately, climate change and water management are making water a waning commodity in freshwater wetlands, facilitating the spread of woody shrubs into wetland sedge communities. Working in subtropical Florida peatlands, researchers found that the leaves of these shrub invaders use water less efficiently, resulting in increased loss of water to the atmosphere despite small increases in carbon uptake.
Wetlands are critical for storage, filtration, and supply of freshwater. However, the dual impacts of human land use and climate drying due to warmer temperatures place these wetlands at risk, particularly in low-latitude regions where dense human populations are expanding. The feedback between external drying driving shrub encroachment and autogenic drying by those shrubs can degrade wetland habitat quality, biodiversity, and ecosystem function, compromising regional hydrology and carbon storage.
Studying sawgrass peatlands of south Florida, researchers from Florida Atlantic University quantified differences in plant photosynthetic efficiency and canopy structure between the historic dominant sedge and encroaching native willow to determine the degree to which vegetation carbon and water cycling is altered by shifts in community dominance. Leaf gas exchange of both carbon dioxide (plant photosynthetic uptake) and water (plant transpiration release) was greater for willow, which also used water less efficiently during photosynthesis (greater water loss per carbon gain). Additionally, the willow’s spreading, multitiered branch growth pattern produced more than double the leaf area index (leaf area per ground area). When scaled to the landscape, the elevated water loss rate and leaf density result in substantial increases in wetland water loss through transpiration with even small spatial extent of shrubs. Autogenic drying of wetlands may also accelerate litter and soil decomposition by increasing aerobic conditions, further compromising the health of these peatlands.
Florida Atlantic University
This work is supported by the Terrestrial Ecosystem Science program of the Office of Biological and Environmental Research (DE-SC0008310) within the U.S. Department of Energy Office of Science, with site data and access provided by the St. Johns River Water Management District.
Budny, M.L., and B.W. Benscoter, “Shrub encroachment increases transpiration water loss from a subtropical wetland.” Wetlands 36(4), 631–38 (2016). [DOI:10.1007/s13157-016-0772-5]