Secondary forest expansion over a savanna domain at an ecological reserve in the Southeastern Brazil after 15 years of monitoring

Abstract

Studies report the forest expansion process toward open savanna areas; however, most of them were conducted by means of satellite images and aerial photographs. This study has investigated the forest expansion process through community dynamics over 15 years of permanent plots monitoring. The study was conducted at a forest continuum of three distinct phytophysiognomies (riparian forest, dry forest, and woodland savanna), sampling the trees with diameter at breast height ≥4.77 cm, distributed into 211 plots (10 m × 10 m). Density and basal area were compared using a paired t test, and Shannon–Wiener diversity was determined through Hutcheson’s t test. The number of dead and recruit trees, and basal area increment and decrement were compared among the phytophysiognomies using variance analysis, followed by Tukey’s test. Dynamics rates were calculated for the interval of 15 years, as well as Jaccard and Morisita-Horn’s similarity indices among phytophysiognomies. In woodland savanna, density and basal area increased and richness and diversity decreased, whereas in dry forest density decreased and richness and diversity increased. No changes in floristic parameters were observed for riparian forest. The similarity among phytophysiognomies increased over time due to advance of typical dry forests species toward woodland savanna and riparian forest; and local decrease in richness of typical savanna species in woodland savanna (decline of 13 species) and riparian species in the riparian forest (three species). From floristic analysis, our results support the dry forests expansion process toward woodland savanna and riparian forest, which seems to be strongly related to the control of fire and decrease in river flow, respectively.