Message From The President
| | I recently walked the Gwynn Falls trail along the Middle Branch of the Petapsco River, a freshwater estuary near Baltimore. It is fed by the Gwynn Falls as well as stormwater outfalls from the heavily urbanized Baltimore area. The Petapsco River is part of the largest estuary in America, Chesapeake Bay, whose watershed reaches well into central New York. As one drives southwest on I-88 from the Capital District toward Binghamton, one soon encounters a sign that reads, “Entering Chesapeake Bay Watershed”. |
| As I walked along the shore through Middle Branch Park, I couldn’t help but notice how polluted this estuary has become. The fact is many of our lakes and rivers that receive urban runoff are threatened by that stormwater. The rains flush oil, gasoline, hydraulic fluids, and many other contaminants directly into bodies of water where complex aquatic ecosystems once thrived. Rainstorms cause combined sanitary sewers and storm systems to overflow dumping untreated sewage into our lakes, streams, and rivers. |
| If our estuaries, rivers, and lakes are to recover, we need to improve our methods of managing wastewater and stormwater. In this essay, I want to focus on how urban forestry can mitigate the harm caused by urban runoff. |
| Even children know that if you run under a tree when it first starts raining, it is dry. Later on, after it stops raining, it is still dripping under that tree. In this way, trees reduce the peak of a rain event. According to the National Tree Benefit Calculator www.treebenefits.com/calculator, a single mature sugar maple can intercept several thousand gallons of stormwater per year. |
It does this by the following:
A. Intercepting and holding rain on leaves, branches, and bark.
B. Increasing infiltration and storage of rainwater through the tree’s root system.
C. Reducing soil erosion by slowing rainfall before it strikes the soil.
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| When we integrate urban trees with wet weather green infrastructure, we reap myriad benefits. Other essays could be devoted to how trees reduce the urban heat island effect, thus improving air quality, saving energy, and making cities healthier places to live. For the purposes of this president’s message, I want to focus on the stormwater benefits. |
| It is the first flush of a rainstorm that can cause the most damage to an aquatic ecosystem. Rain that falls on a hot parking lot and is carried quickly through drains to a body of water can cause rapid temperature swings that negatively impact aquatic organisms. Trees that shade parking lots mitigate this effect in two primary ways; they keep the asphalt cooler and they take the peak off the rain event. |
| When trees are combined with a porous surface parking lot, the resulting biotic and abiotic green infrastructure becomes a powerful system that can greatly protect nearby surface water. |
| One of the coolest examples of this is a very green parking lot that I had the honor of collaborating on with Dr. Nina Bassuk and other partners. It combines porous asphalt, a CU Structural Soil base capable of holding a 100 year rain event, and disease resistant hybrid elms. The trees cool the surface and ambient temperature, slow the rain, and when transpiring pump out pure H2O into the atmosphere. To make this powerful illustration of how trees are an integral component of urban wet weather green infrastructure even more obvious, we sited it next to a flood control channel. No catch basins, water pipes, or outfalls connect to this parking lot! |
| As we continue to manage our urban forest for ecosystem services, and as our ability to quantify those services improves, urban trees will rightly gain importance as biotic components of vital stormwater infrastructure. |
| Andrew Hillman, President |
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