Ujęcie wpływu właściwości gleb piaszczystych na bonitację drzewostanów sosnowych w południowo-zachodniej Polsce w modelach regresji

The research was conducted in 268 pine stands on soils of sandy texture. In the paper 6 regression models for site index of Scots pine (Pinus sylvestris L.) were presented. The soil properties enclosed in the models explained to 40−60% of the site index variability. In the regression analyses, the following soil properties were found to be the best variables that described the site index: pHKCl, contents of fine textural fractions, content of K and N, CaCO3 content, soil moisture conditions reflected in gleying occurrence in a soil profile and a thickness of a solum or of a humus horizon (depending on the site moisture). The CaCO3 content was found to be a useful variable for the site index models only unless other chemical soil parameters were available. In such cases occurrence of CaCO3 in models reflects an impact of K and Mg soil content on pine growth that results from strong intercorrelations between Ca, K and Mg contents in the investigated soils. The site index was higher when pine stands were overgrowing gleyic than non−gleyic soils. In the presented regression models the difference was estimated to be about 1.5 m.