Latest Score:
4.7/5
in 2019
Forest stands can be composed of trees in a variety of sizes. Stands with greater complexity in tree sizes may be more resilient to disturbances and other stressors, and are often more productive^{1}. They can also provide more varied habitat for wildlife and sustain higher biological diversity. Here, stand complexity is assessed using the Shannon-Weiner Index, using the of the proportion of trees per 5" diameter size class.The current year is scored as the difference between the data minimum -10% of the range and the data maximum +10% of the range, scaled to be between 1 and 5.
The score is calculated using a target value and the historical range of the the entire long-term dataset. The higher the score, the closer this year's value is to the target.
Once the score is computed for each year, the trend in scores over time is calculated. If the trend is significantly positive or negative, the long-term trend is marked as increasing or decreasing respectively.
Component | Description |
---|---|
Scored as | Distance between minimum and maximum (scaled 1-5) |
Target value | Data maximum + 10% of the range |
Directionality of scores | Higher values in the data are better |
Minimum value used in scoring | Data minimum -10% of the range |
Maximum value used in scoring | Data maximum + 10% of the range |
Using Forest Inventory and Analysis population estimate data on Phase 2 plots accessed via the FIA Datamart1, we computed tree size class diversity using a Shannon-Weiner Diversity Index calculation (see equation below). The first available data year was 1997. We divided all sampled trees into 5 inch classes and tallied the total proportion of each size class measured in the plots. To compute the annual score, we used FIA’s plot evaluation group panels to create population estimates for each year. The target for this dataset was set as the maximum value plus 10% of the range. The target was set as the upper scoring bounds (dataset maximum plus 10% of the range), and the current year is scored for where it falls between the lower scoring bounds (dataset minimum minus 10% of the range) and the target, scaled to be between 1 and 5.
Shannon-Weiner Index (H’)
Where p_{i} is the proportion of trees in the ith size class
Dataset: VT Tree Table
Dataset: VT Population Evaluation Group Table
Dataset: VT Condition Table
Dataset: VT Plot Snapshot Table
Forest cover is the percent of the state of Vermont with tree cover.
Regeneration of sugar maple seedlings provides information about the future of Vermont's hardwood forests.
Regeneration of red spruce seedlings provides information about the future of Vermont's softwood forests.
Forests with greater stand complexity have trees in a range of sizes and as a result, may be more productive and resilient to stress.
Forest patch sizes provides information on the average size of contiguous forest blocks.
Forest connectivity is a measure of the linkages among Vermont's forests.
With greater diversity in tree species, forests can support more biodiversity, exhibit higher resilience to stress, and store more carbon.
Across the landscape, having a range of forest stand ages provides diversity, varied habitat conditions, and resilience to stressors.