Tuesday, July 21, 2015

Wait! Wait! Don't Pull Me!

Have you ever seen a vine creeping up on a shrub or tree and thought, “Oh, no you don’t! YANK!” That’s good, right?  Not necessarily. I’m Josh Bruce, a Biology major from Vassar College and long-term resident of the greater Philadelphia area.  As a research intern at the Pennypack Trust this summer I am studying the possibility of unintended environmental damage from well-meaning management practices.
Although invasive vines have become an incredibly destructive force on the East Coast—toppling thousands of acres of forests from the edges inward—combating them with brute force may not be the best strategy. In fact, tearing vines out could lead to greater environmental damage than stability in the long term: tree limbs can be accidentally broken, invasive seeds may be spread, and, most importantly, the forest floor can become disturbed.  Uprooting the shallow root networks of invasive vines largely also clears the ground layer of any plants and tree seedlings that are entangled in the invasive plants' roots, leaving bare patches and, even worse, furrows of loose earth like a tilled garden ready for new seed.

Unfortunately this blank space will either be eroded away or filled by whatever can get there first. Since the area was previously invaded, seeds of that very same invasive plant are likely already in the soil. If the original invasive species doesn’t re-invade, hosts of other invasive species have a chance, and a management area can quickly become a foothold for secondary invasion. The initial invader may have had to contend with a thick layer of dead leaves and a diverse community of native plants when it first tried to invade; the newly "managed" site is left with neither of these defenses; therefore, a secondary invasion will likely be even denser and more successful at suppressing native plant regeneration than the initial invasion.
 With my research this summer I am specifically focusing on Oriental bittersweet (Celastrus orbiculatus). This invasive vine, though hard to pull from trees and shrubs, is relatively easy to pull from the soil, making uprooting a tempting management strategy. I have used a 2-meter-wide, custom designed plot frame (a loop of PVC plumbing pipe) to survey the ground cover vegetation in bittersweet-dense areas in the Pennypack Preserve. This gives me a baseline idea of what an initial bittersweet invasion may look like. Following my survey, I either (1) leave the plot alone, (2) cut the bittersweet stems where they emerge from the ground and clip away as much of the top as possible, or (3) rip all traces of Oriental bittersweet from the plot, along with anything else it might have tangled-up in it.
Next year and for several years thereafter, I (or another young scientist) can go back to these plots, survey what has grown or regrown, and repeat the treatments. After several years I hope to be able to say with confidence whether we should or should not use uprooting as a management strategy for Oriental bittersweet, whether clipping the stems year after year is enough to suitably quell an invasion, and what kind of plants are likely to grow in place of Oriental bittersweet that has been ripped or cut. Until then, cutting and carefully removing the top of invasive vines while leaving the roots intact is the safest, if not the most efficient, way to go.
Submitted by:
Joshua Bruce, Research Intern

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