Fig. 5: Primary environmental predictors of tundra greenness trends.
From: Summer warming explains widespread but not uniform greening in the Arctic tundra biome
Variable importance and partial dependence of the six most important variables for predicting site-level Landsat NDVImax trend categories from 2000 to 2016 using Random Forests. The three NDVImax trend categories included browning, no trend, and greening that were based on trend direction and significance (α = 0.10). a Variable importance was characterized by the mean decrease in accuracy, where a higher value indicates that a variable is more important to the classification. b Partial dependency plots illustrate how each predictor variable affects class probability while accounting for the mean effect of other predictors in the model. The top six predictor variables included changes (∆) in summer warmth index (2000–2016), summer soil moisture (2000–2016), and annual mean soil temperature (2003–2016), as well as elevation, summer warmth index in 2000, and annual mean soil temperature in 2003. Soil temperature data were for 1 m depth and were not available prior to 2003. Boxplot lines and whiskers in a depict median estimates and 95% confidence intervals derived from Monte Carlo simulations (n = 103), as do solid lines and error bands in b.
