Trees increase the frequency of cool-season grasses in silvopastoral systems on temperate native grasslands of Uruguay

Abstract Silvopastoral systems may provide important production and environmental benefits. The loss of cool-season (C3) grasses from temperate grazed native grasslands is associated with selective grazing and excessive solar radiation that limits their survival. Silvopastoral systems integrate trees with grasslands that provide shade to both cattle and herbaceous plants, potentially favoring C3 species. There is limited information on the effect of trees on the species and functional composition of native grasslands in the Campos biome in South America. The objective of this study was to detect gradients in the botanical composition of grasslands associated with trees under three conditions: Prosopis on Solonetz, Acacia on Brunisols, and Eucalyptus on Brunisols. Frequency and soil cover of the herbaceous species under trees in each situation was systematically recorded in transects on the four cardinal directions. In all situations, there were differences in pasture composition in the different shade regions. Under the canopy, the herbaceous layer was enriched with cool-season grasses such as Bromus catharticus Vahl, Lolium multiflorum Lam., Stipa hyalina (Nees) Barkworth, and S. setigera J.Presl. At greater distances from trees, cover of warm-season (C4) grasses increased, such as Axonopus affinis Chase and Paspalum notatum Flüggé. The gradients detected allow us to conclude that trees in silvopastoral systems can increase the abundance of cool-season species and potentially improve the forage nutritive value of the native pasture.