Wpływ wybranych właściwości gleby na bonitację drzewostanów dębowych w Nadleśnictwie Międzyrzec

The objective of the study was to determine the impact of selected soil properties on site index of oak (Quercus sp.) stands in the Międzyrzec Forest District (eastern Poland). We utilised data from the soil−habitat survey, which provided information about physical and chemical properties of soils and stand descriptions for 21 oak stands (tab. 1). The collected data served to determine site index (SI), defined as the stand top−height at the age of 100, and soil trophic index (SIG) that is a synthetic measure of the soil fertility. For SI and SIG distributions met the criteria of the normal distribution (Shapiro−Wilk test p−values equalled 0.118 and 0.297, respectively), we applied one−way analysis of variance, t−test and correlation analysis to determine the influence of the forest habitat type and moisture as well as soil properties and fertility measures on the site index of analysed oaks. The SI of investigated oaks ranged from 23.2 to 29.3 m, 26.5 m on average (tab. 2). It was significantly dependent on the site type (F=6.913, p=0.006) with the lowest values on oligotrophic habitat and the highest – on eutrophic one. No effect of habitat moisture content and soil type was found (t=–0.408, p=0.688 and F=2.599, p=0.076, respectively). The SIG values ranged from 20 to 36, with the average of 29.5 (tab. 2). Similarly to the site index, we found significant impact of the forest habitat type (F=5.384, p=0.015) on SIG values. Soil fertility and physical properties significantly influenced site index of the analysed oaks (fig.). We found positive correlation between SI and SIG values (r=0.566, p=0.007) as well as between SI and clay content (r=0.454, p=0.037). Chemical properties of the soils under studied stands seem to have less profound effect on site index of oak. The highest, but insignificant, correlations were found for recalculated acidity (r=–0.420, p=0.056) and magnesium content (r=0.400, p=0.071).