Edge effects at Pleasant Valley Conservancy

In a recent discussion with our summer interns, the topic turned to the movement of invasive species into Pleasant Valley Conservancy from surrounding lands. Good question. PVC is an island of high-quality ecosystems surrounded by invasive-rich lands. I quickly cited the presence of wild parsnip, garlic mustard, reed canary grass, and honeysuckle on neighboring lands. We have worked hard to eradicate these (and other) invasives from PVC, but there are no barriers to keep them from coming in again and again from outside.

Ecologists refer to the changes that occur in a community at the boundary of two habitats as an “edge effect”. (Wikipedia has a nice discussion of this topic.) Small natural areas in particular are subject to these effects because they have large surface/area ratios. (The smaller the site, the larger is the danger from outside. A million acre woods is pretty safe!)

PVC is approximately rectangular in shape, with the shorter dimension about 40% of the longer. This isn’t the worst possible shape for access by invaders, but there are still numerous dangers.

The map shows the major invasives that we have to be aware of.

There is a large patch of wild parsnip (Pastinaca sativa) in our neighbor to the south. This field is immediately adjacent to our Valley Prairie, and every summer we find a few wild parsnip plants that have moved in. Fortunately, dealing with these is not too much trouble, although we worry about forgetting that they might be there.

There is a large area of garlic mustard (Alliaria petiolata) in a degraded woods in our neighbor to the east. This is hidden among prickly ash, walnut, and other woody plants. This was probably the source of the garlic mustard we had in the East Basin when we first started clearing it. Fortunately, the East Basin GM populations were small and easily dealt with. We do have a small patch at the top of our North Woods (Unit 16) that we deal with every year, but it keeps coming back. (The garlic mustard seed bank will last more than 10 years.)

Wild parsnip and honeysuckle are nearby along the county highway to the north (Cty F) and can easily cross the road into our high-quality prairie/savanna road cut. Each year we have to patrol our side of the road (about ¾ mile in length) and pull about 20 or so wild parsnip plants. Honeysuckle has so far not spread.

Reed canary grass (Phalaris arundinacea) is scattered throughout the wetland to our west. We hire a contractor every year to spray reed canary grass in our wetland. 

The important thing is to keep track of the natural area boundaries, since that is where invasive plants will first show up. Fortunately, dealing with these edge effects is not too time consuming or expensive. We just have to be sure we don't forget about them.