Fig. 5: Relationships between tree cover (TC) change 2000-2019 across North American boreal forests and environmental conditions.
From: Northern expansion is not compensating for southern declines in North American boreal forests
a Mean tree cover 2000–2019. b Mean annual temperatures (MAT). c Mean annual precipitation (MAP). Relationships are shown as model fits ± standard errors around the fitted lines for different disturbance categories (colours). Model fits were generated from generalised additive mixed-effects models. Each predictor of tree cover change was included in a separate model due to correlations between predictors. Transects were used as random effects in the models. Additionally, tree cover change was fitted by disturbance type and assuming an exponential spatial correlation structure. Other environmental conditions are shown in Supplementary Fig. 9. Fitted model lines including raw data points are shown in Supplementary Fig. 18. Absolute tree cover change was calculated through Theil-Sen’s slope estimation method and is expressed in absolute terms (see Supplementary Fig. 19 for relative TC change). Climatic variables were taken from the ERA5 Monthly Averaged data set and cover the period 1980–2019 and 2000–2019.
