Combined effects of soil disturbances and tree positions on spatial variability of soil pHCaCl2 under oak and pine stands

Abstract

This study was conducted to investigate the factors affecting small-scale variability of soil pHCaCl2 under homogeneous pine forest monocultures and seed-regenerated oak stands, with particular emphasis on the effects of soil disturbances (windthrows, soil preparation) and tree positions on spatial variability of soil pHCaCl2. We also attempted to explain the mechanism controlling this small scale spatial variability in terms of soil cation exchange properties. Investigations were conducted in forested areas of Southern Poland. Six 20 × 20 m plots were laid out in homogeneous, mature (40–80 years) pine (three plots) and oak (three plots) stands. Soil samples were collected from the top 10 cm of mineral soil in regular 1 m × 1 m grid, what gives 441 samples per plot. Semivariogram analyses indicated a strong influence of former windthrows (mound-pit soil disturbances) on spatial structure of soil pHCaCl2, particularly in soil under oak stands. Moreover, we found that under oak trees soil pHCaCl2 increased with increasing distance from the tree, confirming the presence of so called near tree pHCaCl2 depression. This suggests that the characteristics of mound material are largely a result of the apparent single-tree influence on soil pHCaCl2. Data from pine stands also confirmed that nearby planted tree pHCaCl2 depression was also present; however, variograms characteristics and maps of pHCaCl2 may be proof for stripped pattern of soil pHCaCl2 remaining after soil preparation. Analysis of the cation exchange properties of the soils revealed that variations in soil pHCaCl2 is related to the saturation of soil with Al (i.e., soil having higher pHCaCl2 has less adsorbed H+ replaced by Al3+), while base cations (Ca2+, K+, Mg2+) had no effect, implying that in trees vicinity soil has lower degree of saturation with Al3+.