Monitoring riparian recovery along Darby Creek, Pennsylvania
This fall, I’ve been monitoring the recovery of the riparian community along the Darby Creek in urban, southeastern Pennsylvania. It is the end of the first full growing season following three dam removals in late 2012 and early 2013. While the primary goal of dam removal projects is to remove the direct source of impairment and restore a free-flowing, connected river, these projects often also include riparian, or streamside, plantings – as is the case along Darby Creek.
Riparian vegetation is important for a number of reasons. Immediately following a dam removal, plants help to stabilize exposed soil and reduce erosion. Over the long term, riparian plants provide shade and help to improve water quality by filtering runoff. Fallen leaves from riparian trees that enter the stream every autumn serve as an important source of food for the aquatic community.
Our goal is to plant a mixture of trees, shrubs, and grasses – we include a diverse mix of native trees and shrubs that we would expect to see in a late successional riparian community, as well as fast-growing grasses and shrubs that are easily grown from cuttings (or “live stakes”).
When monitoring riparian recovery we ask: Is there adequate ground cover? Are the “live stakes” surviving? Are invasive species that may threaten future biodiversity and habitat present? Are there additional actions that we need to take to ensure the recovery of the structure and function of the riparian community?
So far, the riparian community at all three dam removal sites is recovering pretty well. Meadow grasses and flowers cover most of the previously bare ground, with the exception of a few well-worn fishing paths and an area on the newly constructed floodplain where sediment deposition appears to have buried the planted seed. Live stakes are thriving at two of the sites, but growth is less impressive at the third site, where we plan to return to add more plantings before the winter comes to help combat bank erosion.
At one site, I noted that a few invasive species, including Japanese knotweed and mile-a-minute, are starting to show up within the restored area. I am working with local volunteers to plan work days to remove these invaders. Most of the trees we planted are surviving, but we lost a few, root ball and all, to a flood that came through before their roots had a chance to take hold. At the site of the former Kent Park Dam I encountered a pleasant surprise – not only are the banks well-vegetated, but the town had decided to stop mowing a portion of an adjacent turf field and a lush wetland has popped up in its place.
I look forward to returning to these sites for a few years to make sure the riparian community is becoming well-established – monitoring streamside plants isn’t a bad way to spend a day or two on the river!