The influence of single trees on saturated hydraulic conductivity (Ks) was investigated for six isolated oak trees (Quercus robur) growing on a Dystric Gleysol in an area of parkland in northwest England. The Ks was measured within the A soil horizon over a 0.10 to 0.25 m depth using a borehole permeameter.

A dataset of 119 Ks values was obtained and comprises of 55 values from around one oak tree at distances of 1 to 13 m from the trunk, 45 tests around five 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 Ks at 3, 5, 7 and 11 m from the trunk and that in the surrounding grassland. Geometric mean Ks 3 m from this tree was 3.35 x 10^-6 m s^-1, a factor of 3.4 higher than that in the surrounding open grassland. Mean Ks decreased at a rate of -4 x 10^-7 m s^-1 per m up to 9 m from the trunk, though it increased at 11 m, before declining again. Similar patterns were observed in the 45 values from the five other oak trees.

A literature review of the potential positive and negative effects of trees on Ks was used to provide tentative explanations for the observed patterns and highlights new data needed.