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Biological Invasions by Jenny Molloy (September 1993) One of the hot topics in the field of conservation biology right now is the issue of "biological invasions" or introduced species, and for good reason. Most of us have heard of the potentially devastating effects of zebra mussels, medflies, kudzu, Japanese beetles, sea lampreys, Africanized honey bees, Dutch elm disease, gypsy moths and a myriad of other organisms that wreak havoc in ecosystems where they do not naturally occur. Other non-native species, like starlings and ragweed, may not create serious problems in their new world communities, but are clearly occasional nuisances. Most of these invasions or introductions occur directly or indirectly through the activities of humans: either as deliberate introductions for ornamental, agricultural or commercial reasons, or as "accidental tourists" like the zebra mussels who found their way from Europe to the Great Lakes in the ballast waters of inter-continental tankers. In addition to the dilemmas that many of these organisms present for humans, they often present an even greater problem for the native flora and fauna. In the absence of their natural predators, parasites, diseases, and competitors, the new arrivals often proliferate unchecked. In the process they can preempt the resources of, or prey on native plants and animals, often eliminating them from the ecosystem. Now not every introduced species fares spectacularly well; some don't make it at all. However, the threat that many of these invaders present has spawned a great deal of scientific research, government legislation, and development of management programs. Invasions in the Augusta Creek Watershed The Augusta Creek watershed has not been immune to invasion. There are numerous plants, animals and other organisms currently residing here that are not native to this region. Some of them are benign neighbors. Others are proving to be more problematic. Following is an introduction to two non-native inhabitants of the watershed that are currently the subjects of ongoing and proposed projects in the Augusta Creek drainage. Brown Trout Brown trout, native to Europe, western Asia and northern Africa, is a species that has been deliberately introduced. Since these fish currently exhibit very little natural reproduction in Augusta Creek, they hardly fit the profile of the insidious invader. There is evidence that Brown trout have preempted the native Eastern Brook trout through aggressive take over of habitat and food resources, and hence Brook trout are now rarely found in Augusta Creek. However, because of changes that have taken place in the drainage and therefore to the creek in the last century (e.g. deforestation, increased erosion), it is possible that the untimely demise of the Brook trout may have eventually occurred even without the introduction of the non-native competitor. The primary motivation for continuing to annually stock Brown trout in Augusta Creek is, of course, to provide good sport fishing. Aside from the harassment of Brook trout, we are not aware of profound negative effects of Brown trout on the Augusta Creek ecosystem. It is possible that the Brown trout may even partially fill the ecological "niche" vacated unintentionally by the Brook trout. However, Brown trout fare best in cool, gravel-bottom, streams with rapid currents and no silt. At best, Augusta Creek provides only marginally good habitat for this trout, as it's inability to reproduce here is testament to. What might happen, however, should the scales be tipped in favor of the Brown trout? The Michigan Department of Natural Resources is planning alterations in Augusta Creek (felling trees over the creek, and dredging out deeper holes in the creek bottom) to improve Brown trout habitat. These changes may or may not have the desired effect for trout, but what other effects might they have as well? We need to consider not only what the direct effects of these habitat manipulations might be on the native biota, but also what the long-term effects of a larger, possibly self-sustaining Brown trout population might be on the Augusta Creek ecosystem. In other streams where Brown trout have become successfully established, many native fish, not just endemic trout, have been driven to the brink of extinction. On the other hand, a self-sustaining trout population would probably improve Augusta Creek fly fishing, and might eventually eliminate the need for extensive stocking. Purple Loosestrife Another interloper, and one which shows all the characteristics of the more devastating invaders, is Purple loosestrife. In the last few years it has gone from a few isolated patches along Augusta Creek, to extensive monospecific stands in watershed wetlands and stream corridors. Purple loosestrife is in bloom for most of the summer and into the fall. It's tall reddish-purple flower spikes are easily noticeable, even from a distance. In the Augusta Creek watershed it is unlikely to be confused with any of the native flora. Loosestrife was introduced from northern Europe over a century ago, and is now quite common throughout eastern North America. It spreads quite successfully on it's own via waterways. However, purple loosestrife has had some help in it's rapid march across the mid-west. Because of it's beautiful purple flowers, horticultural varieties have been marketed for use in perennial gardens, where they easily escape into streams, lakes and wetlands. Beekeepers have also introduced loosestrife into wetlands as a source of nectar and pollen for their bees. Loosestrife has proven to be quite adept at spreading vegetatively and via seed production. In the process it crowds out significant portions of the native vegetation. Wildlife biologists also note that it threatens native birds and mammals because the plants upon which they rely for food, nesting material and shelter have been eliminated, and loosestrife is not a suitable substitute. Early research into biological controls on Purple loosestrife by beetle and wasp predators have yielded somewhat optimistic results. But because release of yet other non-native species caries certain risks, it's unlikely that we will see these loosestrife predators in the Augusta Creek drainage anytime soon. Containment and eradication of Purple loosestrife is difficult, especially along streams and rivers where seeds can be easily transported. Management programs by organizations such as the Michigan Nature Conservancy have met with some success. However, management is complicated. Because of the extensive root systems, manual removal is often difficult, and may do more harm than good. Most herbicides are not approved for use over open water, and may also create more problems than they solve. The potential for re-invasion is also highly predictable, if efforts to remove and control Purple loosestrife aren't widespread and coordinated. To manage this invader effectively requires a watershed-wide, cooperative operation. In the meantime, there is only one practice recommended for individual landowners. Cut off flower heads prior to seed set, carefully remove them from aquatic areas, and burn them. This will not eliminate loosestrife, nor prevent vegetative growth, but it will help prevent seeding of new areas. Because the potential effects of Purple loosestrife are so widespread and serious, the Augusta Creek Watershed Association would like to implement a management program next summer. To do this we need the help of watershed residents. If you would like to be a part of this project, please let us know. Fill out the form below, and drop it in the mail. Postscript Many issues in conservation biology, biological invasions included, are multi-faceted. One person's weed may literally be another's livelihood. Many of these issues remain unresolved because they ultimately come down to value judgements, and different people, quite legitimately, value different things. The Augusta Creek Watershed Association welcomes your opinions and suggestions as we strive to balance issues of native biodiversity with the human uses of the Augusta Creek watershed.

 

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