Vermont Forest Indicators Dashboard


What is forest structure?

Forest structure is the horizontal and vertical arrangement of trees in a forest, as well as the pattern of forest cover on the landscape. Healthy forests have a diversity of species at all different stages of growth. Forest structure can be simple, complex, or somewhere in between . A forest with a simple structure will appear park-like. Trees may be evenly spaced apart and of a similar size and species. Conversely, a forest with a more complex structure will have trees of various sizes and species and unevenly spaced. On a landscape scale, a more desirable structure are forests that span a range of types and successional stages.

Why is structure important to the health of a forest?

Forest structure provides genetic diversity throughout all dimensions of the forest and builds resilience during times of disturbance whether by pests, extreme weather event, fire, or harvesting. In extreme cases, if one species disappears, another is available to take its place. Further, a forest with greater structural and species diversity can supply more ecosystem services, like providing varied habitat and food to a range of wildlife, and supplying a more robust timber resource as markets change over time.

How do we quantify structure into a score?

The Forest Indicators Dashboard includes data from various sources to evaluate structure, including data on tree regeneration, species and size diversity, as well as landscape-level measures, like forest patch size and forest cover.

  • Forest Cover
    Forest cover is an assessment of how much total forest exists in Vermont. For a high score, total forest cover must remain stable over time.
  • Regeneration
    Hardwood and softwood regeneration tell us the future composition of the forests in the future. For a high score, seedlings must have a high density (count of saplings per acre) each year.
  • Stand complexity
    Stand complexity is the proportion of trees per size class. This measure is important in that forests with greater stand complexity are often more productive and resilient to stress. For a higher score, the forest would have to have an equal distribution of tree size classes represented.
  • Mean patch size
    Mean forest patch size is a measure of the average size of forest blocks throughout Vermont. This is important because as we fragment or divide large areas of forest, we reduce the ecological value they provide. Smaller forest patches limit the flow of seeds, animals, and nutrients and can make forests more vulnerable to damage or infestation by non-native pests or plants. Mean forest patch size that does not change from year to year will contribute to an overall higher score for structure.
  • Forest connectivity
    Forest connectivity is an assessment of how close forests are on the landscape. Forest that are widely spaced and have low connectivity mean that animals and plants cannot easily move between patches. Forest connectivity that does not change from year to year will contribute to a higher structure score.
  • Stand Age Diversity
    Across our forests, we want a diversity of forest stand ages, with some forest stands being newly initiated and others having been in place for a long time. This provides us with a diversity of habitat for a range of wildlife, and resilience to varied change. For a higher score, the relative amount of forest by age class should remain stable over time.
  • Species diversity
    Tree species diversity is calculated by the number of different tree species and the relative abundance of each species in the forest. As tree species diversity increases so do forests capabilities to support other biodiversity in the form of birds, animals, insects, and fungi. Further, more diverse forests are more resilient to stress, recover more quickly following damage, and can be more productive. For a higher tree species diversity score, the forest would have to have a high number of species with a fairly equal abundance of each of those species.