Effect of shrub encroachment on vegetation communities in Brazilian forest-grassland mosaics

Abstract

Woody vegetation encroachment in natural grasslands is a concern in many parts of the world. We evaluated the effect of Baccharis uncinella (Asteraceae) encroachment on grassland vegetation in southern Brazil, in terms of plant composition and richness. We conducted a vegetation survey in 12 plots of 10×10m. The study site was a forest-grassland mosaic where management practices have been excluded since 1994. Six plots were located in areas without B. uncinella and the remaining six in different densities of it. Within each plot, we randomly placed three subplots of 1×1m where we identified plant species and estimated their cover. Vegetation height, total plant cover and standing dead biomass were also estimated. We recorded 46 species belonging to 15 families; 34 of them were in plots with B. uncinella (29% grasses, 44% shrubs, 24% forbs and 3% trees) and 37 in plots without it (27% grasses, 35% shrubs and 38% forbs). B. uncinella affected grassland community by reducing total plant richness and decreasing the number of forb species. B. uncinella may alter the availability of resources, affecting the ability of forbs to establish and grow. The capacity of B. uncinella to occupy adjacent open-canopy ecosystems and to suppress grassland plants indicates that, without any management practice, plant richness in Brazilian highland grasslands may decrease. This study presents empirical data that may contribute to conservation efforts of forest-grasslands mosaics in southern Brazil.