Assessing the biotic communities of restored bottomland hardwood wetlands in western Kentucky and Tennessee
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[EMBARGOED UNTIL 12/01/2024] Bottomland Hardwood (BLH) forested wetlands were once the predominant land cover in the Lower Mississippi Alluvial Valley (LMAV), but 75 percent of the historic BLH area has been converted to other land uses, primarily agriculture. This extensive forest loss has led both public and private entities to focus on restoring the numerous ecosystem services such as wildlife habitat, floodwater storage, carbon storage, and nutrient reduction provided by BLH forests in the region. The Wetland Reserve Easement (WRE) Program is a federally funded program that restores wetlands nationwide, with a focus on restoring BLH forested wetlands in the LMAV. Hydrologic and vegetation restoration are two of the typical components of WRE restorations in the LMAV. To assess the current effectiveness of WRE restoration in the LMAV, we evaluated the response of avian, forest, and aquatic invertebrate communities to restoration efforts implemented by the WRE program in western Kentucky and Tennessee. We evaluated the response of forest communities to WRE restoration, specifically because tree planting is a common practice used to restore forested areas on prior converted agricultural lands. We examined whether tree plantings had similar community composition to both reference forests in the region as well as remnant forests on enrolled WREs. We found that established forest types (reference and remnant) had similar community composition, but that tree species composition differed between reference and planted forests and remnant and planted forests. We also assessed the survival of planted trees on WREs in relation to environmental factors known to influence bottomland hardwood tree plantings. Tree survival was greater in younger (0-4 years) tree plantings than in old (10+ years) and middle (5-9 years) tree planting age classes. Tree survival was lower in hydric soils compared to non-hydric soils. Planted tree survival was negatively associated with co-occurring tree density and height above the nearest stream drainage. Tree survival increased with sapling density and with distance to the nearest remaining forest patch. We also assessed the response of avian density and richness to local and landscape level environmental variables on WRE study sites. We found that avian richness and density responded more strongly to local scale habitat factors than to landscape level factors. The most important habitat variables explaining avian species richness were forest age and canopy cover, whereas the most important habitat variable explaining avian density was forest age. Mature forests had significantly greater avian richness than both middle and old restored forests and forest canopy cover was positively associated with avian richness. Middle aged forests had lower avian densities than mature forests. None of the models containing landscape configuration or landscape composition at either a local or a landscape level were competitive in our model comparison, so we did not interpret results from those models. Finally, we investigated the response of aquatic invertebrates to hydrologic restoration performed on WREs in western Kentucky and Tennessee. We constrained our evaluation of invertebrates to study sites that contained Shallow Water Areas (SWA) restored by either ditch plugs, water control structures, or levee/basin methods. I assessed the response of aquatic invertebrate functional feeding group (FFG) biomass and richness in restored SWAs in comparison to level of floodplain connectivity (overbank connected or overbank isolated). Functional feeding groups response to hydrologic connectivity varied across groups, with greater predator biomass and richness in overbank isolated wetlands, and greater scraper biomass and richness in overbank connected wetlands. I also examined how flooding in different seasons (spring, winter, and fall) impacted aquatic invertebrate FFG biomass and richness. The presence of autumn flooding increased predator and gathering collector biomass but decreased detrital shredder biomass. Autumn flooding increased the taxa richness of predators, scrapers, and gathering collectors. I also examined ecosystem attributes provided by restored WREs based on the proportions of various FFGs and functional habit groups (FHG). Based on the FFG and FHG proportion analysis, restored SWAs were heterotrophic systems, with above average predatory invertebrate control, a healthy invertebrate food supply for benthic feeding fish and wading birds and an invertebrate community capable of rapidly colonizing newly inundated habitat.
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M.S.