Tree planting is considered a best management practice (BMP) for stormwater management. In some respects, trees are the original stormwater BMP, as the gold standard of stormwater management is to reproduce the hydrology of woods in good condition. Trees reduce the quantity and increase the quality of stormwater runoff while also providing many other ecosystem services to our local community.
Stormwater Best Management Practice (BMP) – Stormwater BMPs are strategies for reducing the amount of stormwater runoff or improving the quality of that runoff to reduce or eliminate pollutants reaching local streams and waterways. Ecosystem services – Ecosystem services are the benefits to humans provided by healthy ecosystems.
- How Do Trees Manage Stormwater?
- What Other Ecosystem Services Do Trees Provide?
- What are the Types of Tree BMPs?
How Do Trees Manage Stormwater?
- Trees slow and capture precipitation in their canopy.
- More than 20% of annual rainfall is retained by a tree’s canopy.
- Some of this precipitation is then evaporated or transpired by the tree. Trees can transpire up to 540 gallons/day.
- Precipitation that is not captured in the canopy may be directed down the trunk as “stemflow”
- Up to 15% of the precipitation captured by the canopy is directed down the trunk to be intercepted by the soil.
- Tree roots and the accumulation of leaf litter under trees promote infiltration of precipitation into the soil.
- By reducing the volume and rate of stormwater flowing to local waterways, trees can help to reduce streambank erosion, thereby reducing sediment and pollutants flowing downstream.
Urban Tree Impacts on Hydrology and Water Quality
Taken from Recommendations of the Expert Panel to Define BMP Effectiveness for Urban Tree Canopy Expansion. Chesapeake Bay Program Report CBP/TRS-312-16
What Other Ecosystem Services Do Trees Provide?
In addition to stormwater management, trees provide many ecosystem services that may go unnoticed. These include providing wildlife habitat, recreation, improved air quality, and shade. Did you know studies have found:
- Trees can increase your property value.
- Trees can reduce stress.
- Trees can reduce the temperature of city streets by 2-4 degrees F.
- Trees can reduce obesity levels, by encouraging more physical activity.
- Trees can reduce rates of cardiac disease, strokes and asthma due to improved air quality
Harford Streams is focused on using the following Tree/Forest BMPs recognized by the Maryland Department of the Environment for stormwater management:
Urban Tree Canopy Planting:
The Urban Tree Canopy Planting BMP involves planting trees in areas with a managed turfgrass understory that is regularly mowed. There are opportunities to expand this type of tree planting throughout the County, both on public and private properties. Harford Streams is working with Harford County Parks and Recreation and Harford County Public Schools to expand tree planting on their properties.
The Forest Planting BMP involves creating a forested area that is at least a half-acre with an unmanaged understory that is not fertilized or mowed. The forest must have a density of at least 100 trees per acre and at least 50% of the trees should have a diameter of 2 inches or greater measured at 4.5 feet above the ground (or a one-inch caliper at the time of planting).
Harford Streams is working with Harford County Parks and Recreation, Harford County Public Schools, and Harford Community College to expand forest planting on their properties.
Riparian Forest Buffers:
The Riparian Forest Buffer BMP involves creating forested buffers within 100 feet of perennial streams. Riparian buffers zones are crucial to a healthy watershed because these zones act as a last line of defense for our local streams and waterways. Trees have extensive root systems that help to filter pollutants from stormwater runoff, stabilize slopes, and absorb large amounts of water during and after rain events.
Harford Streams is working with Harford County Parks and Recreation to expand riparian forest buffer planting on their properties.