Issue At Hand

Oak forests throughout the world are in a state of decline due to lack of oak seedling recruitment to larger size classes. Much of this recruitment decline has been attributed to changes in ecosystem disturbance regimes that have led to increased competition from other species. The Midwest Driftless Area forests in the United States are currently dominated by large oak trees of three species: white, bur, and red oaks. These oak forests currently provide habitat for a large variety of flora and fauna, recreational opportunities for people, and an important timber resource.

Of concern are nonnative species of buckthorn (Rhamnus cathartica) and honeysuckle (Lonicera tartarica) shrubs that commonly invade forests across the Midwest. Once established in forest ecosystems, they have the potential to significantly alter tree recruitment, herbaceous diversity, and nutrient dynamics.

What We Hope to Accomplish

To inform timber and biodiversity management in the Midwest Driftless area, we examined the current status of forest composition and structure of Midwest Driftless Area oak forests. We were specifically interested in understanding how the invasive buckthorn and honeysuckle might contribute to the decline of oak recruitment.

What We Found

We found that the recruitment of oak species is poor in comparison to other canopy tree species, including sugar maple and American basswood, and that the majority of saplings are of non-oak species. Our results revealed strong associations between bur oak, common buckthorn, and sites with high levels of soil nutrients. These same site characteristics were disassociated with white and red oak. Common buckthorn was determined to have an edge effect that may place it in direct competition with oak seedlings in areas that show the most promise for oak recruitment.

Our research suggests that invasion by and competition from common buckthorn may be of substantial concern when managing oak stands dominated by bur oak. Buckthorn seems to be less of a problem at present within white or red oak-dominated stands, though attention should be placed on controlling buckthorn invasions from the edges of these stands.