Sweet-smelling forest threat. (Clippings).

As large-scale agriculture shifts west and portions of the northeastern United States return to woods, forest recovery and species diversity are being challenged by a sweet-smelling but aggressive adversary, honeysuckle.

Three Asian species, L. maackii, L. tatarica, and L. japonica, were introduced 100 years ago as useful plants, but most land managers now consider them highly undesirable, aggressive weeds. Amur honeysuckle (L. maackii), for example, was widely promoted by the U.S. Soil Conservation Service, along with multiflora rose. Together, they've taken to the woods throughout the Midwest. Oops.

Amur honeysuckle has become the dominant shrub in both forests and open areas from Appalachia to the upper Midwest, forest researchers say. It does best in disturbed forest patches with large amounts of edge or open canopy. In the woods, fast-growing and early-maturing honeysuckle inhibits canopy tree regeneration and reduces the abundance of native trees, shrub, and herbs. Birds help disperse the huge quantity of small red fruits it produces. The shrubs, which leaf out early and hold their leaves late in the season, are not susceptible to many pathogens or herbivores.

David Gorchov at Miami University in Ohio and J.O. Luken at the University of Kentucky are among the researchers to show that when Amur honeysuckle becomes abundant in a forest area, native seedlings disappear from the understory. Even shade-tolerant sugar maple seedlings are inhibited by honeysuckle, and native annuals such as jewelweed and clearweed decline rapidly. Honeysuckle's impact on native tree, shrub, and herbaceous seedings has the potential to alter the future structure and composition of forests, since many forest canopy species depend on light gaps for regeneration--gaps that are no longer there.

Only intensive cutting and repeated herbicide treatment can halt the invasive shrub's spread. Occasional cutting only makes it grow faster, and the expense in labor and materials for repeated treatment is prohibitive for large areas. Invasive honeysuckles are still sold for residential and commercial use, don't invite them to your forest.