Green Horizons

Stormwater BMPs are Best Management Practices that communities can adopt to mitigate stormwater runoff and the effects of harmful chemicals that they may contain. They can be grouped into five categories and trees can be used in each category.

Wet Ponds are constructed stormwater retention basins designed to retain a permanent pool of water. They are generally located in the flow-path of the runoff. The wet pond provides for sedimentation, which removes metals, nutrients, sediments and organics from stormwater. Biological uptake of pollutants and nitrogen is provided by vegetation in and around the pond. Wet ponds are suitable for sites with high nutrient loads.

Examples of trees suited for wet ponds would be red buckeye, buttonbush, burr oak and baldcypress.

Wetlands. Actually, we are talking about constructed wetlands when talking about stormwater BMPs. Directing stormwater to natural wetlands damages the hydrology and functioning of the wetland. Like their natural counterparts, constructed wetlands offer aesthetic qualities, wildlife habitat, erosion control and pollutant removal. They may be used alone or in conjunction with other BMPs. It is very important that a sufficient supply of water be provided to ensure proper functioning of the wetland.

Pawpaw, green hawthorne, winterberry holly and black gum are just a few examples of tree species that can be established in constructed wetlands.

Infiltration Basins take advantage of existing permeable soils to provide groundwater recharge. The runoff is captured and allowed to infiltrate into the ground and be lost to evapotranspiration. Pollutants are removed as water flows through the soil and are exposed to bacterial action. Vegetation planted in these basins takes up nutrients and their roots provide arteries for stormwater to permeate the soil for groundwater recharge.

Flowering dogwood, persimmon, hophornbeam and chinquapin oak can be successfully planted in infiltration basins.

Surface Filters (including pocket sand filters) include a permeable medium such as sand for stormwater quality control. They can be used in areas with low soil infiltration rates, high evapotranspiration rates and hotspots.

The planting soil layer may not include significant clay content that would hinder infiltration and help retain moisture for plant growth. So, “dry site” tree species like serviceberry, scarlet oak, blackgum and shortleaf pine are in order for these areas.

Bioretention Areas are attractive landscaping features planted with perennial native plants. They are designed to absorb runoff from impervious surfaces such as roofs and parking lots. These BMPs can be used in settings from residential landscapes to “big box” sites, or anywhere in between. They should not be confused with rain gardens promoted for homeowner installation, which are beneficial but do not involve rigorous engineering to meet stormwater standards. Bioretention areas are generally designed with underdrains.

They are full of water during storms and dry out between rain events. So, trees planted in these areas need to tolerate both extremes. Musclewood, redbud, witchazel and white oak are good choices for bioretention areas.

In addition to stormwater BMPs, trees affect sidewalks, streets and other community features. To encourage thoughtful consideration of both trees and community infrastructure, the Missouri Community Forestry Council’s 17th Annual Conference, “Integrating Trees into Municipal Infrastructure” is scheduled for March 16-18, 2010, in Chesterfield, Mo. For more information, see pg. 12, contact Donna Baldwin (573) 751-4115 x3111 or go online to www.mocommunitytrees.com/conference.html