Plant-community responses to shrub cover in apáramograssland released from grazing and burning

Abstract

Shrub encroachment can follow grazing or burning release in páramo grasslands. While encroachment decreases herbaceous species richness in some grassland systems, the effects of this process on the herbaceous community in páramo grasslands are currently unknown. We collected data on shrub cover, herbaceous-species cover and species composition in a páramo grassland 12 years after release from burning and cattle grazing near Zuleta, Ecuador. Topographic and soil measures were also included as predictor variables of differences in community composition. Contrary to studies in other systems, shrub cover did not have a significant effect on herbaceous-species richness, whereas shrub-species richness significantly increased with shrub cover. However, shrub cover was associated with significant shifts in herbaceous–community composition. Most notably, there was an increase in some shade-tolerant forbs and tall-statured wetland grasses with increasing shrub cover, and a corresponding decrease in some short-statured grasses and early successional forbs. These results could indicate that the ameliorative effects of shrubs (e.g. frost and wind protection) in harsh alpine environments may partially compensate for the expected competitive effect of shrubs due to shading.