Tree community dynamics in the cerradão (2002-2016): A case of biome shift

Abstract

The cerradão is the result of profound structural changes from open Cerrado vegetation, associated with the absence of certain disturbances, such as wild fires. Little is known about these changes in the long term, both in species composition and structure after canopy closure, hindering predictions regarding the community trajectory. Cerradão is positioned along the higher biomass extreme in the Cerrado phytophysionomic gradient. This study is based on the changes recorded over a 14 yr period, in 256 plots totaling 10.24 ha of sampling area, in a cerradão located inside a conservation unit, protected from fire for at least 60 years in the state of São Paulo, Brazil. The changes in the community structure and species composition were assessed. We investigated if the changes are related to tree community structure or to biological attributes of the species, especially by their habitat preference (savanna specialists vs. generalists of forest species). Despite the long period without disturbance and the dystrophic soils, we found tree basal area still increasing and the largest trees still growing. On the other hand, tree density is decreasing over time, and 54% of trees recorded in the first survey had died 14 years later. Community diversity had only a slight increase over time, due to a small gain in species richness. Forest and generalist species presented higher increments in basal area and faster growth compared to the rare savanna specialists still alive in the community. We also verified that larger trees grow slightly faster than smaller trees. Although these changes point to an increase in competition, mortality was not correlated with tree basal area, and seemed to happen more randomly at community level. However, mortality and recruitment were not random at species level. We detected increase in abundance of forest and generalist species, which are shade tolerant. The lowest recruitment rates and highest mortality rates were associated with typical open Cerrado species (savanna specialists), that tend to disappear over time, consolidating the biome shift from savanna to forest. The contribution of cerradão to the conservation of Cerrado endemic tree species, therefore, is poor and tends to decrease over time.