| Summary: | The study conducted in a tropical dry ecosystem at Cañas, Guanacaste, Costa Rica (10o 11´ N and 84o15´W) measure the standing herbage biomass (SHB) availability and quality under six isolated tree species of different canopy architecture dispersed in active Brachiaria brizantha pastures and compare it to that growing at full sun light. Standing herbage biomass (HB) harvesting and Photosynthetic active radiation (PAR) readings were taken at three different periods in a paired sample scheme. Of the six tree species studied, Enterolobium cyclocarpum had the largest mean crown cover while Acrocomia aculeata had the smallest. Significant differences were observed between species (P = 0.0002) and seasons (P<0.008) for the percentage of PAR transmitted under the canopy but PAR levels obtained under all species were consistent throughout seasons since the interaction between species and season was not significantly different (P=0.98). Lower PAR readings (<50%) were taken under the canopies E. cyclocarpum and Guazuma ulmifolia (21.7 and 33.7 % respectively). Standing herbage biomass (SHB) harvested under the crown of isolated mature individual tree species was significantly lower (P<0.001) than in open pasture areas for all tree species except that of A. aculeate but SHB crude protein content, was higher underneath all tree canopies. It can conclude that light reduction caused by tree canopies reduces SHB availability and increases the quality underneath tree canopies compared to areas of full sun but these varies accordingly to tree species and seasons.
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