Post-establishment vegetation control in two pine saw-timber stands in South Africa

Abstract

In pine plantations, the effect of shading following canopy closure reduces the growth of competing vegetation. In some pine stands, particularly those grown for saw-timber, full canopy closure is not achieved due to a combination of the low initial planting density, pruning and thinning. This means that the important competitive characteristic of complete shading is lost, resulting in stands with the potential to support competitive levels of post-establishment vegetation. At the time of the first pruning operation, two trials were established, one on a 4.5-year-old P. patula and one on a 2.9-year-old P. tecunumanii stand to determine the competitive effect of post-establishment vegetation on tree growth. Besides a weedfree and weedy treatment, the selective control of either the herbaceous vegetation (grasses and annual broadleaved plants) or all the perennial woody broadleaved plants was carried out in either the woody or herbaceous treatments. Only the woody perennial broadleaved plants were removed prior to any pruning event in the commercial weed control treatment (operational). These treatments were maintained until the trees were thinned (over nine successive growing seasons) with tree performance monitored over this period. There was no significant tree growth or survival response to competition from post-establishment vegetation for the duration of the trial.