Using plant life to manage storm water & control erosion
Beyond the ways plants sustain humans directly, they also offer many other benefits, including creating a beautiful and stable environment. Environmental stability can refer to many things, but in the context of mitigating the effects of storm water and related erosion, plants offer many benefits.
Plants directly cover the surface of soil, reducing the amount of surface erosion from rainfall that would otherwise only be possible with hard surfaces. They also grow roots that directly absorb water, as well as provide physical channels in the soil for water to infiltrate. In addition, roots physically hold the soil together. Different plants have different root structures, and not all plants offer equal soil-holding capacity.
Together, plant roots, soil and their underlying substrates comprise the framework for an extensive underground ecology that provides habitat for an array of life. Some of those life forms are crucial to long-term plant health, such as mycorrhizal fungi. Others, such as micro-organisms, insects and mammals, modify the soil structure over time to make it more porous and receptive to storm water infiltration. We enjoy these benefits simply by choosing to use plants instead of hardscapes to curb and not exacerbate soil erosion downstream.
Ongoing human-caused environmental impacts add another dimension to this topic.
“The last word in ignorance is the man who says of an animal or plant, 'What good is it?'" said Aldo Leopold, former professor of wildlife ecology for the University of Wisconsin-Madison. “If the biota, in the course of aeons, has built something we like but do not understand, then who but a fool would discard seemingly useless parts? To keep every cog and wheel is the first precaution of intelligent tinkering.”
Leopold offered one of the first hypotheses around the importance of species diversity to long-term survival. Heeding his advice in the application of plants in green infrastructure projects, we must find ways to assist in the perpetuation of diverse plant life on earth by making better decisions about the types of plants we are encouraging to cover the earth’s surface.
In the U.S., the largest single-species crop covering the land is turf grass. This is a discretionary crop that mostly demands that we expend resources instead of providing any tangible benefits to us, other than propping up cultural conventions. Since turf grass is inexpensive to install, it is understandable why it dominates. However, its long-term costs to maintain and associated environmental impacts rarely are accounted.
Relative to soil erosion, turf grass is not the best performer. It often fails to provide anything more than green cover due to typically shallow and weak root systems. Whenever possible, a project team should consider another type of green cover as a long-term erosion control solution. Native plants offer the benefits of deeper and denser root systems. We may agree to want and support more biodiversity; however, working landscapes are subject to extra pressures (think road salt runoff into bioswales). Only the toughest native plants can withstand these conditions.
Even so, the list of these species is much greater than the short list of non-natives that often are the cheapest and easiest to acquire, grow and maintain. Non-native species also can be invasive and can threaten important remaining natural areas that we may someday depend on. At a bare minimum, invasive species must not be planted as an erosion control solution.
I challenge those that can make decisions regarding their soil erosion control needs to specify a more diverse species palette, and to alter their maintenance paradigms as needed to best support more diverse native plantings that are increasingly important to our collective future.