Fig. 3: Forest growth dynamics and their relationship with δ15N across Swedish regions.
From: Rising atmospheric CO2 reduces nitrogen availability in boreal forests
a,b, Annual forest volume growth (m3 ha−1 yr−1) for P. sylvestris (a) and P. abies (b) by region—north, central, southeast and southwest Sweden—over 1950–2017. Significant linear regression slopes (P < 0.05) are in bold; however, piecewise linear interpolation is shown for enhanced visualization. c, Predicted δ15N (‰) values as a function of relative forest volume growth change (m3 ha−1 yr−1) accounting for random effects (grid) and fixed effect of absolute forest volume growth (m3 ha−1 yr−1). d, Predicted δ15N (‰) values as a function of relative forest volume growth change (m3 ha−1 yr−1) accounting for random effects (grid) and fixed effects of total basal area (m2 ha−1). Regression lines show modelled δ15N values accounting for all fixed and random effects. Shading in c and d indicates 95% confidence intervals. Data sources are cited in Methods.
