By: Daniel Price
Plants are an interesting metric to assess environmental health. The common thought that “green is good” when observing non-developed spaces is natural as the alternative is no green in these hyper-developed areas. However, green is not created equal. Some of the green found in Pennsylvania and throughout the U.S. are known to be invasive. Invasive plants are non-native (not from the region) and well-adapted to outcompete the native plants. These plants are great at spreading rapidly and taking or making more efficient use of the resources plants need (think sunlight, water, nutrients). The presence of invasive plants can negatively affect the living organisms that share the same space, putting more stress on an ecosystem.
One area greatly affected by invasive plants is the watershed. A watershed encompasses the land in which all the rainfall and snowmelt make its way into smaller waterways, like streams and creeks, to eventually flow into a larger body like a lake or ocean. Simply, it’s where a drop of rain will go after it falls. The drop of rain will eventually evaporate or transpire before once again becoming a drop of rain, completing the water cycle. As an organism that needs water to survive, plants are often found in abundance surrounding streams and rivers. A key area plants inhabit is called the riparian zone. The riparian zone is the land directly next to a body of water. Being next to each other, the riparian zone and the waterway have a unique relationship where the contents of one influence the other. Invasive riparian plants can disrupt the normal relationship between the riparian zone and the waterway. One method invasive plants can disrupt this relationship is by releasing toxins to suppress the growth of other plants or changing the pH of the soil to become too basic or acidic for native species to survive. These plants are known as allelopathic. A common allelopathic plant seen throughout Pennsylvania is garlic mustard (Alliaria petiolata). Garlic mustard is not exclusive to the riparian zone but can often be found inhabiting that space.
Garlic mustard (Alliaria petiolata)
Other invasives like the Japanese knotweed (Reynoutria japonica) which grows very densely, can alter the amount of sunlight the stream and other plants receive, negatively affecting their health. Invasive plants can often take up and retain water differently than native plants. This can lead to discrepancies in the natural relationship between water and waterways. For example, an invasive plant may not require as much water as a native plant, leading to a greater chance that nutrients enter a waterway via runoff, rather than being absorbed by a plant.
Japanese knotweed (Reynoutria japonica)
Image from Oklahoma State University
A watershed is a highly connected system where slight changes can largely affect the organisms that inhabit it, including humans. Humans are very much a part of the watershed and need to better understand that the actions taken or not taken, greatly affect the health of that ecosystem. A simple way to help combat the spread of invasive riparian plants is to plant native. Regardless of where you plant invasives, they often find ways to spread to more sensitive areas like the riparian zone. The PA Department of Environmental Protection has released a field guide of common invasive plants, detailing how to identify and potentially control these plants in your local area (see link at bottom). Here at Willistown Conservation Trust, the Stewardship Program holds Stewardship Thursdays, where you can volunteer to help reduce the spread of invasive riparian plants, care for newly planted native trees and shrubs, and help establish healthy habitats in public spaces. With a little bit of work and awareness, the spread of invasive riparian plants can be combated.
Link for PADEP Field Guide – https://www.dep.state.pa.us/dep/deputate/watermgt/wc/subjects/streamreleaf/Docs/Invasive%20Plants.pdf
