Stormwater management basins (SWMB) are commonly used to mitigate runoff from developed areas. While the ecology of SWMB varies, cattails (Typha latifolia) frequently colonize basins in the United States, even those designed for dry detention. Managing agencies usually consider large cattail populations undesirable and request cattail eradication.  Woody plants may alter the dynamics of cattail growth, but are typically removed from SWMB. We conducted two studies to assess the feasibility of using trees to reduce cattail populations by altering growing conditions, specifically shade and soil moisture. In a greenhouse study we tested the impact of three shade and soil moisture treatments on cattail growth.  Shade treatments (full sun, medium shade, heavy shade) were created using shade cloth (no shade cloth and 73% or 92% shade cloth respectively) mounted on frames. Soil moisture treatments (dry, moist, flooded) were maintained by daily monitoring (watered after 0.12 MPa, 0.045 MPa and flooded 3-5cm above the soil respectively). In a second study in four unmaintained SWMB in Lynchburg, Virginia, all vegetation was harvested from one hundred 0.25-m² plots and biomass of different plant constituents measured. Woody vegetation influence index (WVII), water table levels, and soil organic matter content were also determined for each plot.

Results/Conclusions

Effects on cattail biomass after two months indicated a strong interaction between soil moisture and shade (p<.001). Increases in shade and reductions in soil moisture resulted in decreased biomass and rhizome length. Shade decreased biomass most in flooded conditions and reduced soil moisture decreased biomass most in full sun. Cattails in dry soil and heavy shade had 95% less total biomass and 83% smaller rhizomes than cattails in flooded soil and full sun. Within full sun, dry soil decreased below-ground biomass by 85% and above-ground biomass by 94% compared to flooded soil. Even moist soil decreased above- and below-ground biomass by 63% and 56% respectively. Decreases in moisture reduced leaf width and suppressed cattail physiological processes. In the second study, principle component analysis revealed water table is an influential variable with a close relationship to cattail biomass. In addition, the environmental gradient represented by the first principle component favored cattails but negatively influenced woody vegetation. These results imply trees and cattails grow in different conditions, but whether they compete with each other is unknown. The first study suggests trees have the potential to eliminate cattails; however more research is needed to determine the implications of tree growth in SWMB.