Changes in floristic composition and pollination systems in a “Cerrado” community after 20 years of fire suppression

Fire is considered a major factor in the succession process in “Cerrado”, determining the dynamics and composition of these Neotropical savanna plant formations. However, when savannas are protected from fire, both fire-tolerant and fire-sensitive plant species increase in density and size, especially species of trees. Nevertheless, how this change in the vegetation structure relates to changes in the ecosystem function has been seldom evaluated. Pollination is a major ecosystem service, and here we aimed to determine possible changes in floristic composition, floral biology, and pollination systems in an area of open savanna protected against fire over a period of 20 years in Minas Gerais state, Central Brazil. The comparison over the two decades showed that ecological succession, in the absence of fire, increased the diversity and decreased the dominance of plant species. There was an increase in specie richness from 156 spp. in 1992 to 206 spp. in 2012, with appearance of trees and species with specialized pollination systems. Plants were predominantly pollinated by bees in both periods, but floral diversity and specialization seem to have increased after fire suppression, for instance, with the emergence of more species pollinated by moths. Not only generalist light-colored actinomorphic flowers, but also tubular or cup-like nectar flowers commonly associated with more specialized pollinators predominated in both periods. The dominance of these contrasting features actually increased after two decades, especially when we compare the number of individuals in each group. However, it seems that the increase in plant diversity and density of woody species did not lead to marked specialization of floral features and pollination system along the studied period.