Fig. 3: Range-average % forest stability index (FSI) across size distributions of the eight most abundant tree species in the western US over the period 2001–2018.
From: Over half of western United States' most abundant tree species in decline
Population decline (red) occurs when the FSI is negative and the associated confidence interval does not include zero. Conversely, population expansion (blue) occurs when the FSI is positive and the associated confidence interval does not include zero. Here, the %FSI is a direct measure of average annual percent change in the relative density of each species across their ranges in the western US, and variation in the FSI across species-size distributions is indicative of shifts in forest structure during the study period. Total % change in relative density can be estimated by multiplying the %FSI by the length of the study period (18 years), with a maximum annual decline of −5.56% (complete loss of the population over the study period). Source data are provided as a Source Data file.
