Soil disturbance impacts on early growth and management of radiata pine trees in New Zealand

In the mid-1980s, trials were established in Esk and Ngaumu Forests to determine the effect of five graded levels of skid trail usage (i.e., logging-induced soil disturbance) on the growth and early management of the next crop of trees. This article reports results of measurements taken up until the Esk trees were 16 years old and the Ngaumu trees were 14 years old. Soil disturbance influenced both soil penetration resistance and weed competition; soil penetration resistance was greatest on the heavily disturbed areas, and weed competition was greatest on the undisturbed areas. Up until the time when the trees were first precommercially thinned, there was no clear relationship between disturbance levels and tree malformation. Only heavily disturbed areas in the Ngaumu trial showed increased levels of mortality. Fastest height and diameter growth occurred on minor skid trails where a certain amount of soil disturbance had taken place. Trees on completely undisturbed sites grew almost as poorly as those on the most disturbed areas (major skid trails). This difference was still evident in tree volume measurements at mid-rotation; i.e., about 15 years old. Soil disturbance also influenced the early management of the trees. Heavily disturbed areas had fewer trees selected for low pruning and more trees selected for precommercial thinning.