Estratégias CSR em assembleias herbáceo-subarbustivas em cronossequência de florestas tropicais sazonalmente secas

Abstract

The CSR theory has been used to explain the dynamics and structuring of plant assemblages although it has been little used in examining chronosequences in low-production environments. The present work investigated variations of CSR strategies and the floristic composition of the understory vegetation in low-production environments in the tropical semiarid region of Brazil. We evaluated the hypothesis that environmental stress was the most important factor for determining survival strategies throughout the chronosequence in understory plant assemblages (herbs, herbaceous vines and sub-shrubs), although the type of stress and the floristic composition would be expected to vary along the chronosequence.. Research was undertaken in three sites in seasonally dry tropical forest (SDTF) vegetation in the semiarid region of Brazil. Floristic surveys of the understory vegetation were performed in each of the three sites at chronosequences intervals of 5, 25 and 45 years, collecting plants and specimens of branches with leaves to measure their functional attributes (leaf area, specific leaf area, and dry mass content) and classify their CSR strategies. The data was processed for grouping analysis and analysis of variance (ANOVA) to better understand the variations in floristic composition and the changes in the predominance of survival strategies along the chronosequence. We found that floristic compositions varied over the chronosequences, generating species substitutions. In a similar manner, CSR strategies varied according to successional ages, with gradual substitutions of strategies. Our results indicated that CSR strategies in Seasonally Dry Tropical Forests are distributed in a gradient between the S and R extremes, with a median CSR strategy – arguing against the hypothesis that stress tolerance strategies would be predominant in low-production environments. When the sites were analyzed separately, the importance of each strategy varied distinctly along the chronosequence, making it impossible to detect a consistent pattern – probably due to rainfall variations. We conclude that variations in disturbance and stress levels at local scales, typical of dry environments, cause species substitutions in the understory vegetation to be quite dependent on variations of specific climatic conditions at each locality, making it difficult to predict long-term successional strategies.