Basal area as a strategic indicator for forest component management in silvopastoral systems: insights from long-term experiments

This study aimed to evaluate the effect of tree shading in silvopastoral systems (SPS) on forage production through long-term experiments, as well as to determine the correlation between dendrometric variables of eucalyptus trees and transmission of photosynthetically active radiation (PAR) to establish thereby the optimum forest cover for effective management in these systems. We evaluated four SPSs in São Carlos, SP (21° 57′ 42″ S, 47° 50′ 28″ W, 854 m.) and Campo Grande, MS (20° 24′ 55″ S, 54° 42′ 26″ W, 530 m.), Brazil, considering various factors such as tree age, management, and density. The systems included pastures with eucalyptus (Eucalyptus urograndis) or corymbia (Corymbia citriodora) trees planted in single rows at densities ranging from 83 to 357 trees ha⁻¹. During the rainy season, from October to March, we analyzed the correlation between PAR transmission and relative forage production (forage production in the SPS/forage production in full sun), as well as the correlation between dendrometric variables, such as diameter at breast height, volume and basal area per unit area and PAR transmission. The results showed a linear reduction in production in the SSPs due to the decrease in PAR transmission. The strongest correlation between tree growth and PAR transmission was obtained with the basal area per hectare variable (r = − 0.91). Thus, this study successfully established a linear relationship between basal area per hectare and PAR transmission, providing insights for the implementation of tree thinning management in SPSs to maintain the productive potential of forage plants in the understory of these systems.