The impact of vegetation control on the establishment of pine at four sites in the summer rainfall region of South Africa

Abstract

Synopsis Four trials designed to study the impact of intensive, selective and commercial vegetation control (operational) practices on pine establishment were implemented across an altitudinal and climatic range ofsites in the summer rainfall region ofSouth Africa. The trial sites incorporated one high altitude (1650 m a.s.l.) cooltemperate site, two mid-altitude (l000 m a.s.l.) warm temperate sites and a low altitude (60 m a.s.l.) sub-tropical site. Treatments implemented at each trial included a weedy and a weedfree control, operational weed control, selective control of herbaceous or woody vegetation types as well as a ringweeding treatment at three sites. The results indicate that the abundance and type ofvegetation at a site varies as a functlon'of'tha local physiographic and environmental conditions as well as historical land-use. At the high altitude site the competitive vegetation was less abundant than at the mid-low altitude sites where vigorous woodyvegetation dominated. Due to the differential growth ofvegetation across the sites, tree growth responses to intensive and selective vegetation control were site dependent. There were no significant tree growth responses to vegetation management at the high altitude site. Relative to the weedfree control, tree growth suppression was highest on the weedy and woody treatment plots at the warmer, mid-low altitude sites. No significant suppression of tree growth occurred where the vegetation was kept away from the trees, on the ring-weeded and operational treatment plots. Herbaceous vegetation caused significant tree growth suppression only where climatic conditions were conducive to extended seasonal growth.