Influence of individual oak ( Quercus robur) trees on saturated hydraulic conductivity

Abstract

The influence of single trees on saturated hydraulic conductivity ( K s) was investigated for six isolated oak trees ( Quercus robur) growing on a Dystric Gleysol in an area of parkland in northwest England. The K s was measured within the A soil horizon over a 0.10–0.25 m depth using a borehole permeameter. A dataset of 119 K s values was obtained and comprises of 55 values from around 1 oak tree at distances of 1–13 m from the trunk, 45 tests around 5 other oak trees, and 19 tests in open grassland. For the intensively sampled tree, Wilcoxon rank sum tests showed a significant difference ( p < 0.05) between the median K s at 3, 5, 7 and 11 m from the trunk and that in the surrounding grassland. At 3 m from this tree, the median and geometric mean K s were a factor of 2.3 and 3.4, respectively, larger than those of the open grassland. Further, the geometric mean K s decreased at a rate of −4 × 10 −7 m s −1 m −1 from 1 to 9 m from the trunk, though it increased at 11 m, before declining again. A similar pattern in geometric mean K s was observed in the 45 values around the five other oak trees. A literature review of the potential positive and negative effects of trees on K s was used to provide tentative explanations for the observed patterns and to highlight the new data needed to support more robust interpretations.