Forest Health

Why are invasives such a big problem?

Invasive plants disrupt ecosystem function and forest productivity in numerous ways. Understanding the problems these plants create is the first step toward reducing their spread. 

Invasive plants cause the following problems:Glossy Buckthorn invasion

  • Replacement of native species. An understory of invasives causes the diversity of plants to drop, replacing native spring wildflowers, native shrubs and tree seedlings. However, native plants support greater insect biodiversity, which provides food for birds.

  • Interruption of natural succession. In Vermont, most abandoned farm fields would typically revert to forests, but in some areas of the state, it is now common for honeysuckle or buckthorn to grow so thick that it is difficult for this natural succession to take place. 

  • Decreased forest regeneration. Tree seedlings cannot get enough light and frequently perish when dense populations of invasive plants are present.

  • Disruption of the food chain. Native wildlife often avoid feeding on invasive plants. This is particularly true for insects: most moths and butterflies rely exclusively on specific species of native host plants. When their population numbers drop, it eliminates a critical food source for birds, fish and many other wildlife.

  • Degradation of habitat. Invasive species have become the single greatest threat to the National Wildlife Refuge System, according to the U.S. Fish and Wildlife Service. They are causing widespread habitat destruction and the decline of native wildlife and birds.

  • Hastened erosion. Japanese knotweed, for example, lacks a strong root structure, does a poor job of anchoring riverbanks and can increase sedimentation and erosion, which increases phosphorus runoff into rivers. 

  • Altered soil chemistry. Invasives impact soil chemistry, which naturally dictates what grows where. For example, buckthorn can increase soil nitrogen levels, and garlic mustard can disrupt beneficial associations between tree seedling roots and fungi (called mycorrhizal associations), which suppresses tree regeneration.