University of Vermont Extension

Forest Biodiversity: Threats to Biodiversity

The major threats to Vermont’s forest biodiversity are simplified forest structure, habitat loss and fragmentation, introduced invasive species, overbrowisng by deer, and climate change. Explore each dropdown block to learn more.

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Simplified Forest Structure

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Because of past land use, today most of Vermont’s forests are relatively young and simplified. Many are “even-aged” stands that established after intensive clearing or were “high-graded” for the most valuable lumber. These forests often lack the variety of tree species, large trees, dense understories, and decaying wood that many species depend on. This simplification has reduced the diversity of habitats across the landscape, impacting species tied to the extremes of forest development – very young forests and very old forests.

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Habitat Loss and Fragmentation

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Vermont continues to lose roughly 5,000 acres of forest each year to other land uses. This conversion fragments formerly continuous forest blocks into smaller patches, limiting the movement of animals, plants, and fungi, reducing available habitat, and increasing vulnerability to invasive species and climate stress.

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Introduced Invasive Species

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Introduced Invasive plants, animals, insects, and pathogens – often spread through trade, travel, and landscaping – outcompete native species and lack natural predators. Invasive insects such as emerald ash borer and hemlock woolly adelgid threatened keystone tree species and the many organisms that rely on them. Invasive plants such as Japanese barberry, honeysuckle, and buckthorn crowd out native wildflowers and tree seedlings, alter soil and light conditions, and offer poor-quality food for wildlife.

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Overbrowsing by Deer

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High browsing pressure from white-tailed deer reduces regeneration of tree seedlings and wildflowers, leading to simplified forests dominated by a few unpalatable plants. This lowers habitat quality for birds and pollinators and reduces resilience. 

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Climate Change

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Warming temperatures, shifting precipitation patterns, and more frequent storms are already changing Vermont’s forests. Species that depend on cold conditions — such as balsam fir and moose — are declining, while southern species move north. Extreme weather events can damage trees, increase erosion, and stress regeneration. 

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