Composition and diversity patterns of terrestrial herb communities in old-growth and secondary South Brazilian Atlantic Forest

The conversion of old-growth into secondary forest changes profoundly the community structure of most plant life-forms, including the communities of terrestrial herbs. Here, we verify how herb communities are affected by environmental variables of old-growth and secondary stands of South Brazilian Atlantic Forest. We identified all herbaceous species and estimated their frequency and cover in 16 plots of 6 x 6 m in each forest type. We used the structural characteristics of the tree component (i.e., basal area, density, average height and canopy openness) and soil parameters as environmental variables of each forest. Results showed that old-growth and secondary forests have distinct herb composition, with the later showing higher plant cover and species diversity. Canopy openness and soil parameters explained part of the variation in herb composition between forests. Herb cover and richness responded positively to soil fertility in both forests, and in secondary forest these two descriptors were also positively correlated with canopy openness. The abiotic differences between forests allowed the establishment of herbaceous species with different ecological requirements, especially in the secondary forest, marked by input of species typically found in disturbed environments. These species contribute to the higher cover values and species richness in secondary forest. Our findings suggest that changes in environmental conditions in a forest substantially change the herb community. Because of their importance as environmental indicators, herb communities can contribute to a better understanding of successional patterns in the Atlantic Forest.