Structure of herbaceous communities in areas with different natural regeneration periods in the Brazlian semi-arid

The species composition and forest structure may change due to human disturbance. Changes in the arboreal component in regenerating forests has frequently been determined, but data on the herbaceous component are less available, especially those of tropical dry forests, despite their ecological and economic importance. Thus, in regenerating dry forests in the Brazilian semi-arid area, we tested the hypotheses that: (1) richness and diversity of herbaceous species are higher, but biomasses are lower in areas with longer regeneration periods; and (2) the aboveground herbaceous component is restricted to the rainy season, and species diversity, plant density and biomass vary with different patterns along this season. Four regeneration periods were analyzed: 2 (R2), 17 (R17), 39 (R39) and more than 60 years (mature caatinga) after grazed planted pasture was discontinued. The herbaceous component began growing after the onset of the rainy season (January) and disappeared in July after the rains ceased. Richness and plant density were highest in March, whereas biomass was highest in April and May. Mature caatinga and R39 had the highest herbaceous species richness (61 species), but the lowest biomasses (167 and 98 g m-2), with the opposite occurring in R2 (48 and 381 g m-2). Alpha diversity was highest in the mature caatinga, but beta diversity in R17. As a result, the herbaceous diversity increased while the plant density and biomass decreased as the regeneration period increased.