The influence of single trees on soil permeability was investigated for six isolated oak trees (Quercus robur) growing on a dystric gleysol in an area of parkland in northwest England. Soil permeability was measured within the A horizon of the soil at fixed depths of 0.1 to 0.2 m using a borehole permeameter. Detailed study was initially undertaken around a single tree. Mean permeability was determined for distances from 1 to 13 m from the tree at 2 m intervals and compared with the mean permeability of the surrounding grassland soil. T-tests showed a significant difference between the soil permeability 1, 3, 5, 7 and 11 m from the trunk of the tree and in the surrounding grassland. There was no significant difference 9 and 11 m from the tree. Mean permeability 1 m from the tree was 5.05 x 10-6 m s-1, a factor of 3.1 higher than the surrounding grassland soil. Mean permeability decreases with distance from the tree up to 9 m from it. Further measurements were then taken from around the five other trees and grouped with the data collected for the first tree in order to test if the pattern evident around the first tree was evident for all isolated oak trees at the site. A general pattern was confirmed and it was concluded that a circle of influence affecting the mean permeability of the soil around isolated oak trees on a dystric gleysol has been confirmed.