Wednesday, January 14, 2009

Invasive species increase threat to forests

From the Grand Traverse Herald

By BILL COOK, MSU Extension Forester

An invasive species can change the way a forest works. Typically, these changes are regarded as harmful. Tree regeneration fails. Habitat for certain wildlife species diminishes. Ecological functions become disabled. A native species within a forest disappears.

Sometimes a species from another place will "invade" a forest and cause an ecological imbalance. Other times, an imbalance will allow a local species to behave in an invasive manner. Both situations are difficult (and expensive) to correct.

Exotic species come from another place; could be another continent or could be from another part of the state. Recently, species such as the emerald ash borer, oak wilt, and beech bark disease have made quite a stir. Buckthorn and garlic mustard creep along the forest floor. Other species have made the news in non-forest vegetation types, such as purple loosestrife and zebra mussels.

Historically, we have lost trees such as chestnuts and elms to diseases. Blister rust hobbles the return of white pine. Gypsy moths eat their way through oaks and aspen. In the future, there are impending threats to pine, hemlock, maples, and other common species.

When ecological balances are upset, native species can cause problems. Deer can all but eliminate tree regeneration and spring flowers. Pennsylvania sedge prevents newly germinated seeds from surviving. Bracken fern produces chemicals that may prevent other plants from growing. Too much edge between forest and field may allow cowbirds to nearly eliminate nestling chicks.

The presence and impact of invasive species is increasing. In order to combat the spread and prevent introductions to new areas, we will have to change some of our behaviors. First on the list would be to stop moving firewood around. Firewood is recognized as a major carrier of several unwanted hitch-hikers.

ATVs carry plant seeds, such as spotted knapweed. The spread patterns of several invasive species follow those of vehicle access into the forest. We may have to become more diligent about inspecting and cleaning our vehicles. The same is true about boats and fishing habits in keeping Eurasian milfoil and viral hemorrhagic septicemia (VHS) out of our lakes.

Landscaping our properties and seeding-in roads and log landings should be done with native species or exotic species that we know are not invasive. If you're not sure, then why take the risk? As more people move into the forest, the presence of houses, lawns, and related development has an impact. This is especially true along lakes and rivers, where some of our most valuable habitat exists (or existed?).

Not so very long ago, we didn't have to worry about invasive species. These days, there is much more human activity in the forest and there are a growing number of invasives ready to take advantage of an opportunity to establish and/or spread. We live in a different world with some different rules. If we want to maintain as much of "nature" as we can, then we need to heed the new rules.

The emerald ash borer is the most recent example of an invasive species that has caused hundreds of millions of dollars in damage and control costs. Cities struggle with the expense of either protection or the removal and replacement of millions of street trees. Home owners experience property value loss and, in some cases, increased air-conditioning bills during the summer. In the forests, ash is an important component of wetlands, has a niche role in forest products, and for American Indians has a large cultural impact.

Imagine the effects of losing our maples!

The list of "lost" forest species grows longer with time. Many natural resource specialists cite invasive species within the top three threats to forests, and natural environments in general. Prevention or early detection are the best ways to combat invasive species, but both of these require the cooperation of everyone.


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