Impacts of Changing Hydrology and Hurricanes on Forest Structure and Growth Along a Flooding/Elevation Gradient in a South Louisiana Forested Wetland from 1986 to 2009

Abstract

Alterations to Louisiana’s coastal landscape during the last 200 years have resulted in major changes to the natural hydrologic regime. Hurricane and tornado winds further impact coastal forests by exacerbating conditions that affect community structure, growth, and regeneration. Twenty-three years of study of forested wetlands in the Lake Verret watershed provide an opportunity to relate changes in forest communities to precipitation, drought, storms, and rising water levels. The area had two communities in 1986, but four communities were present by 2009. A major change in community composition occurred in drier sites after Hurricane Andrew (1992), when Chinese tallow (Triadica sebifera) became established. Swamp plots were generally not affected by hurricanes, but composition continued to change as a result of flooding. After Hurricane Andrew, net primary productivity (NPP) declined dramatically until 2001. Subsequent hurricanes in 2004 and 2005 also caused reductions in NPP, but recovery was rapid. Low-lying and transition areas are trending from bottomland communities toward more of a deepwater swamp as baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica) increase their stature, likely due to the system-wide flooding. Natural ridges are flooded less often and have remained primarily bottomland, though Chinese tallow (Triadica sebiferum) numbers increased following Hurricane Andrew.