Effect of grazing exclusion on the woody weed Rosa rubiginosa in high country short tussock grasslands

This study investigated the effects of the removal of sheep grazing on sweet brier (Rosa rubiginosa) in montane short-tussock grassland. Sweet brier is an invasive woody weed of economic and conservation significance in hill and high country. Destructive sampling of a range of sweet brier plants indicated that both volume and height are good predictors of sweet brier biomass. Brier density, cover and plant size were measured in five exclosure plots free from grazing and adjacent grazed grasslands near Otematata, South Canterbury. An ungrazed block provided a further contrast. Brier was significantly taller and had higher cover and densities in the ungrazed sites. The total numbers of plants in all size classes were reduced with grazing, except for the smallest size class at one site. There were proportionately more small (0.5 m) plants at grazed sites. Our results suggest grazing is reducing sweet brier invasion and the abundance and vigour of existing plants.