Environmental Controls on Installed Woody Plant Establishment in the Hydrologically Restored Tidal Freshwater Wetlands of the Nisqually River Delta
Guthrie, Caitlin Rose
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Tidal freshwater wetlands are some of the most highly productive wetland systems on the planet. However, alterations to the land surrounding major Puget Sound river deltas have resulted in a 60% to 83% loss of tidal wetlands. As our awareness of ecological services grows, and freshwater tidal wetlands rise in restoration priority, understanding the environmental controls on this native habitat type is of the utmost importance. Currently, a lack of scientific knowledge leaves data gaps for tidal swamp restoration implementation. The purpose of this study was to determine the relationship between restored tidal processes and installed native woody plant establishment in a Puget Sound tidal swamp. In this observational study, we determined survivorship, growth and vigor of installed plants, while also measuring numerous environmental controls, including: elevation, water table depth, competition, salinity, and soil characteristics (moisture, pH, texture, bulk density and organic matter). Planting success was significantly correlated with elevation, depth to water table, salinity, soil organic matter, and soil bulk density. Increased planting success occurred at higher elevations, deeper water tables and lower salinities. At growing season salinities above three ppt and at elevations below one half of a meter above mean higher high water, planting success was greatly reduced. However, specific installed species, including Malus fusca, Lonicera involucrata and Rosa pisocarpa survived at higher rates in these marginal conditions. By gaining an understanding of processes and natural patterns, we are able to advance the efficacy of future Pacific Northwest tidal forested restoration projects.
- Forestry