Effect of Tree Shade on the Yield of Brachiaria brizantha Grass in Tropical Livestock Production Systems in Mexico

Trees play an important role in livestock grazing lands, but the effect of tree shade on grass productivity has not been studied widely. In this study, we evaluated the effect of tree shade on grass yield in pasturelands with dispersed trees in the humid tropics of Mexico. We sampled two livestock grazing systems: 1) scattered native trees in paddocks composed of Cordia alliodora and Cedrela odorata trees with Brachiaria brizantha cv. ‘Xaráes’ grass; and 2) scattered trees in paddocks composed of C. alliodora, C. odorata, and Guazuma ulmifolia, with B. brizantha cv. ‘Marandú’ grass. We established isolation cages at different distances from trees: 1) under the tree canopy, 2) on the border of the tree canopy, and 3) out of reach of the tree canopy, to measure grass yield, grass height, dry matter content, and senescent biomass from April to September. The effect of tree shade on grass yield was significant, with the highest grass production under the tree canopy compared with grasses that grew on the border of the tree canopy and in full sun. We found the highest forage yield in June for B. brizantha cv. Xaráes and the lowest yield in September for the same grass. During July and August, B. brizantha cv. Xaráes yielded the greatest average height, with the lowest values during April and May for B. brizantha cv. Marandú. The greatest dry matter content was recorded in September for B. brizantha cv. Xaráes. Additionally, the most senescent mass was recorded in June and the lowest in April for the same grass. Native trees that persist in grasslands positively influence forage yield during the dry season. Increasing the productivity of the grasslands by agroforestry practices may represent a valuable alternative to mitigate the negative effects of deforestation caused by extensive livestock farming.