What a pleasure it is to move through the Green Mountains like elves through Middle Earth, taking only deep breaths and leaving only footprints.
Um, those footprints? The boots that made them? They may forever alter the mountains. For you, a hiker, may be carrying about the seeds of non-native invasive plants.
Worldwide, loss of habitat is the biggest cause of the loss of native biodiversity - the naturally occurring populations of plants, animals, and microorganisms that uniquely characterize unspoiled spots on our planet. The second biggest? Invasion by non-native plants.
Vermont lists more than thirty species as designated noxious weeds, which "outcompete and displace plants in natural ecosystems and managed lands." Among the terrestrial plants on the list, some are moved from place to place primarily by birds (Asian honeysuckles, the buckthorns, and Oriental bittersweet); others by wind (Tree of heaven and pale swallow-wort); or water (Japanese knotweed and common reed, for example).
Two invasive species, however, are commonly moved about by people - people driving mowing machines, people riding mountain bikes and ATVs, and people on foot.
Purple loosestrife needs little more than moist soil, sun, and a little disturbance to crowd out its neighbors and the creatures that depend on them. Monospecific purple loosestrife wetlands are biodiversity deserts, at least as compared to the real things.
Garlic mustard prefers the moist shade typical of Vermont forests. We've known for years that it can outcompete spring wildflowers. A recent study shows it can harm trees - by killing off the native soil fungi that help trees take up nutrients. Garlic mustard may be as destabilizing and intractable as is acid rain.
Both purple loosestrife and garlic mustard produce a gazillion seeds. Thousands of these bits of destiny can be picked up on clothing or boot soles at the parking lot, at the road crossing, or under the power line. Germinating, growing up, and setting seed in their new location, they continue their linear invasion via the next unwitting hiker.
Some conservation organizations have set up boot cleaning stations at trail heads, though they admit the stations are better at educating the public than preventing the spread of seed. (Turns out the brushes serve as reservoirs of contamination for the next pair of boots.)
Better ideas are:
This article first appeared in Green Mountain Club's Long Trail News Trail Mix section in Spring 2007.