Supervivencia estival de macollos de gramíneas C3 en sotobosque forestal

Given the increasingly intense, hot, and dry summers in subtropical regions such as Uruguay, where the persistence of certain winter grasses may be jeopardized, it is crucial to design effective strategies that enhance their survival within livestock production systems, particularly those based on pastures. We hypothesize that the conditions created by a silvopastoral system (SPS) reduce tiller mortality in perennial C3 grasses that are better adapted to shaded environments. This study assessed the tiller dynamics of two perennial C3 grasses with contrasting shade tolerance (Dactylis glomerata: tolerant; Lolium arundinaceum: moderately tolerant) and one biennial C3 grass typical of humid environments (Holcus lanatus), under full sun and SPS with tree rows-oriented north–south (N–S) and east–west (E–W). Eucalyptus grandis significantly altered the understory microclimate, reducing photosynthetically active radiation (PAR) and moderating both air and soil temperatures. The N–S orientation allowed greater penetration of radiation into the understory compared to E–W. Tree-based systems lowered summer soil temperatures by approximately 3°C relative to the control treatment. Soil moisture was higher under E–W orientation during the warm months. D. glomerata emerged as the species with the highest tiller density in the understory at the end of the first summer, particularly under N–S orientation, due to greater survival and continuous establishment compared with L. arundinaceum and H. lanatus. In contrast, L. arundinaceum exhibited reduced survival and tiller emergence under trees, despite maintaining high density under full sun. Its tiller density and survival were strongly associated with PAR and soil temperature, while soil moisture exerted little influence. H. lanatus, meanwhile, suffered high mortality across all treatments, with complete tiller disappearance in the understory by the end of summer. Overall, the findings suggest that in subtropical climates, silvopastoral systems can enhance the persistence of D. glomerata during the warm season, ensuring its survival and population stability.