Shade, Moisture, and Woody Vegetation in Stormwater Management Basins: Influence on Cattail (Typha spp.) Growth

Stormwater management basins (SWMB) are used to mitigate urban runoff. The Virginia Department of Transportation relies on dry detention basins planted with mowed turfgrass. However, these basins often retain water; resulting in cattail (Typha spp.) and tree colonization. Managing agencies request cattail eradication and trees are also removed. However, if trees were allowed to remain they could alter basin dynamics, making conditions unsuitable for cattails.

In a greenhouse study we tested the impact of three shade (heavy, medium, full sun) and soil moisture (dry, moist, flooded) treatments on cattail growth. After two months, cattail biomass indicated a strong interaction between soil moisture and shade (p<.0001). Increases in shade and reductions in soil moisture resulted in decreased biomass and rhizome length. Heavy shade and dry soil produced the most reductions in cattail growth (95% less biomass, 83% smaller rhizomes than cattails in full sun and flooded soil). However, considerable growth reductions still occurred in medium shade and moist soil (66% for biomass and 74% for rhizome lengths).

In a field study in four unmaintained SWMB in Virginia, environmental data (litter layer, water table, soil organic matter, etc.) and vegetation composition (cattail and other herbaceous biomass, and woody vegetation influence index) were collected from 100, 0.25-m2 plots. Principal component analysis indicated cattails and trees occupy opposing environmental spaces. Water table is most strongly correlated to cattail biomass. While these results suggest trees could eliminate cattails from SWMB, more research is needed to determine the long-term impacts of trees on basin function.