Swamps of coastal Louisiana are hydrologically isolated from the Mississippi River, highly impounded by manmade structures, decimated by saltwater intrusion, and have experienced land subsidence resulting in more frequent flooding, for longer periods. Restoration plans call for re-introducing Mississippi River water to increase sediment elevation, promote natural regeneration, and enhance overall production. In addition to anthropogenic stressors, repeated, often severe, defoliation of the two dominant tree species by the univoltine forest tent caterpillar (Malacosoma disstria Hubner) and the baldcypress leafroller (Archips goyerana Kruse) occurs at the onset of each spring and adds further stress to these forested wetlands. One objective of our ongoing laboratory and field study is to evaluate the effects of multiple stress agents on the declining health of ecologically important forested wetlands. To isolate the tree responses to each individual stressor and the potential combination of stressors, seedlings were subjected to treatments in a 2x2x2x2x3 factorial in a greenhouse. Treatments included 2 tree species, 2 defoliation levels, 2 nutrient regimes, 2 hydrology regimes, and 3 salinity levels. Defoliation significantly reduced diameter growth, but did not interact with the varing levels of salinity, flooding, or nutrients. However, the combination of flooding and increased salinity significantly reduced diameter growth compared to seedlings subjected to salinity and not flooded. In field studies, fertilizer inputs (to simulate nutrient loading from a river diversion) did not affect tree productivity after one year. Further, the effects of lepidopteran defoliation and resultant nitrogen loading rates from frass production will be discussed.
Species 1: Lepidoptera Lasiocampidae Malacosoma disstria (forest tent caterpillar)
Species 2: Lepidoptera Tortricidae Archips goyerana (baldcypress leafroller)
Keywords: stress, defoliation
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