#93 Roadside Travelers
June 26, 2008
This show originally aired in July, 2007 and then again on June 26, 2008 on “The Rivanna Rambler,” a weekly public affairs show airing every Thursday at 11:55 a.m. on WTJU 91.1 FM or wtju.net
Summer time is travel time – and for some of us involves hours in the car, watching the road, the clouds, the passing scenery. On a recent trip to Orkney Springs, I took stock of summertime’s fullness: the tree-covered mountains fuzzy with blossom, the roadside grasses, prolific and head-heavy with seed. I recognize chicory’s cheerful blue flowers, along with Queen Anne’s lace, mullein, and thistle.
Once at our destination, I take to foot along a rough macadam road headed towards West Virginia. Walking uphill at a leisurely pace, with a field guide in hand, I stop from time to time to identify those flowers I do not yet know. Bouncing Bet, or soapwort, with its generous flowering orbs of pale pink and white; New York ironweed, tall, stately, with emerging purple flowerets. Oxeye daisy, everlasting pea.
For better or for worse, roadways are as good as any for seeing wildflowers, in part because in clearing a swath through the trees suitable for roads we make it possible for other plants to thrive. Some of these are native species that have found a new stronghold, and many are not so welcome, belonging to that category of plants we call non-native. On national and state lists, they are ranked according to their cumulative affect on habitat: plants on the C-list generally do not affect ecosystem processes, but establish themselves to the detriment of native plants. “B” list plants are moderately invasive, effecting ecosystem processes on at least one level. A-ranked species, as you can guess, are the worst offenders, causing major alterations in plant community composition and structure, while disrupting the ecosystem process on many levels.
And along this back road in the Alleghany foothills, I come face-to-face with a leggy purple-flowered plant, looking much like field thistle, but distinguished by the dark colored fringe on the bract at the base of the flower that gives rise to it’s name: the spotted knapweed, or Centaurea maculosa. In Virginia, it’s an A-list plant – and it is also much reviled by habitat protection specialists in the western United States, where it was first introduced. Also known as “ballast weed,” it is believed to have arrived in the 1890’s in the soil used as ballast on ships coming to the Pacific Northwest.
Once established, the spotted knapweed out-competes the natives by a number of methods. It has a highly efficient taproot that sucks up water faster than the root systems of its neighbors. It is relatively unpalatable to herbivores; and it is prolific, each plant producing up to 25,000 seeds that are dispersed by wind, animals, and people. The seeds themselves are hardy and may remain viable for 8 years. Massive eradication programs are underway to protect native grass pastures and rangeland in the west that have been overtaken by this species. And while it is on the A-list in Virginia and other Bay states, most resources in the mid-Atlantic have been spent going after the really bad herbaceous actors: purple loosestrife and phragmites.
In the 1970’s, agricultural agencies began to introduce two species of gall flies, whose larvae build galls within the flower buds, thus reducing the number of seeds produced. In an ironic twist of fate, it turns out that deer mice find tis larvae quite tasty and often ingest the knapweed seeds while munching on the fly larvae. The great-horned owl, in turn, finds the deer mouse a yummy treat, regurgitating the indigestible mouse parts, along with knapweed seeds when done with its meal, contributing to further dispersal of the plant species. This highlights an important fact: once introduced, whether intentionally or by accident, species become part of large ecological webs, usually with unforeseen consequences.
And there’s another consequence of the knapweed’s successful adaptation to altered landscapes like this roadway I am walking. As the network root system of the native species is replaced by the knapweed tap roots, the water storage capacity of the soil decreases, resulting in increased runoff and soil erosion. Think stormwater. Think sedimentation. And think about how these affect water quality of streams and tributaries.
Habitat alteration is an ongoing process, since the beginning of time by animals, including man, and by the forces of nature — landslides, windstorms, floods, and lightning induced fires. No doubt, I am changed by traveling to communities distant from my home, but I am, as well, an agent of change on that distant community. This seems a worthy thing to ponder as we face a summer of confronting our global impact.