Latest Score:

4.4/5

in 2019

score trend is down over time
Weight: 10%

Stand age diversity represents the presence of a large range of age classes in the forest. The age of the trees in a forest provides us a sense of the amount of time since a stand-replacing disturbance event has occurred, such as a hurricane or a timber harvest. Across our forests, we want a diversity of stand ages, with some stands being young and new and others being old and in place for a long time. This provides a diversity of habitat for a range of wildlife, and resilience to change. Here, we use stand ages (in 40 year grouping) extracted from Forest Inventory and Analysis data1 to quantify the proportion of our forest in three age groups: very young (0-40 years), young (41-80 years), and mature (81+ years). A higher score means that the relative amount of forest by age class is remaining stable over time.

1USDA Forest Service. 2017. Forest Inventory and Analysis National Core Field Guide, Volume 1: Field Data Collection Procedures for Phase 2 plots. Version 7.2. Available at: https://www.fia.fs.fed.us/library/field-guides-methods-proc/docs/2017/core_ver7-2_10_2017_final.pdf

-- Expert interpretation for Stand Age Diversity is not available--

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

Long-term mean

Directionality of scores

No change from the long-term mean is better

Minimum value used in scoring

Data minimum -10% of the rang

Maximum value used in scoring

Data maximum + 10% of the range

Using the USFS Forest Inventory and Analysis Program data accessed via the FIA EVALIDator1 , we extracted the acreage of forest for every 20 year age class. We re-categorized stand ages into 40 year buckets (0-40, 41-80, and 81-140 years) and computed age class diversity using a Shannon-Weiner Diversity Index calculation (see equation below). Per FIA protocol, plots were reassessed every 5 years until 2014 (i.e. data reported for 2007 used 2003, 2004, 2005, 2006 and 2007), and then every 7 years after that2. The target for this dataset was set to the long-term mean, and the score was then computed as the deviation from this target, scaled to be between 1 and 5.

Shannon-Weiner Index (H’)

Where pi is the proportion of trees in the ith size class

1 USDA Forest Service. 2019. FIA EVALIDator. Available at: https://apps.fs.usda.gov/Evalidator/evalidator.jsp
2 USDA Forest Service. 2017. Forest Inventory and Analysis National Core Field Guide, Volume 1: Field Data Collection Procedures for Phase 2 plots. Version 7.2. Available at: https://www.fia.fs.fed.us/library/field-guides-methods-proc/docs/2017/core_ver7-2_10_2017_final.pdf

STRUCTURE INDICATORS