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Minnesota-North Dakota-South Dakota

Science Update

Story Highlights
  • Long-term impacts of deer browsing
  • Changes for forest composition
  • Lower productivity

Foresters and ecologists, like home landscape enthusiasts, are well aware of the damage deer can do on trees and shrubs. The impacts of browsing on young tree seedlings are well-known and have been documented in the scientific literature for decades. Elevated deer populations intensify these impacts. More than 17,000 peer-reviewed articles have been published on the topic since the early 1990s. 

But what are the long-term consequences of all this munching? Is elevated browsing changing the forests of the future? TNC Forest Ecologist, Mark White, has been working on answers to these questions. The results of his study, which spans two decades, have just been published in the April, 2012 issue of Forest Ecology and Management. In an old-growth forest in northeastern Minnesota, he examined how excessive deer browsing has changed the forest over the past two decades. In areas left open to deer browsing, signature species such as white cedar and white pine have been wiped out. Even more common species such as quaking aspen, paper birch, and black ash have been set back. In contrast, fenced areas from which deer were excluded have had healthy gains of many of these species. 

The overall character of the forest has also changed. At the start of the experiment, the site was predominantly mixed conifer-hardwood forest with a super-canopy of white pine and red pine. As the older trees have died, deer browsing has been so intense that few younger trees have been “recruited” to take their place. The result is open woodland with scattered white spruce, which is not palatable to deer. The resulting forest is much less productive, which is bad for nature and people. 

Excessive browsing is just one of the stressors contributing to north woods conditions that are much changed from those we think of when we say we are “going up north.” One of the consequences is that these simplified forests are considered less able to cope with new threats on the landscape, from a warming, drying climate to novel insect and disease outbreaks.   

In anticipation of these challenges, The Nature Conservancy is working with partners to bolster the ability of northern forests to adapt. Using planting, restoration forestry, and collaborative land management, we are working to keep the “woods”  in the Northwoods.

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