Fig. 2

Universal kriging variogram model γ (discontinuous line) fitted to the residual variogram (hollow circles) and linear combination of the fitted variogram model and \( \sum \limits_{\mathrm{i}}^{n(d)}\sum \limits_{\mathrm{m}=1}^p\sum \limits_{\mathrm{j}=1}^p{\beta}_{\mathrm{j}}{\beta}_{\mathrm{m}}{\left({X}_{\mathrm{j}}\left({\boldsymbol{s}}_{\mathrm{i}}\right)-{X}_{\mathrm{m}}\left({\boldsymbol{s}}_{\mathrm{i}}+h\right)\right)}^2 \) (continuous line) vs empirical semivariogram (filled circles) of the stem density (N), basal area (BA), and quadratic mean diameter (QMD) in a Forest Management Unit 1 (FMU 1), b FMU 2, c FMU 3, and d FMU 4