Aporte de serrapilheira e chuva de sementes como bioindicadores de recuperação ambiental em fragmentos da Floresta Atlântica

Abstract

Although fragmentation affects Forest structure and dynamics, there are few studies correlating their impact to seed rain and litterfall. The aim of this study was to compare and evaluate spatial and time patterns of seed rain and litterfall in four remnants in Atlantic Forest based on their isolation degree and size, in order to apply these traits as bioindicators of environmental degradation. In each isolated (F3= 3.2 ha; F4= 62 ha) and connected fragments (F2 = 8 ha; F1= 23 ha) of different sizes 16 seed traps were established in four distance from the border and sampled during 11 months, during 2004. Pearson coefficient, principal component analyses (PCA), species indicator and cluster analyses were performed to define the relationships among species, seed rain, litterfall and fragments characteristics. In order to compare the fragments were compared using Shannon-Weaver (H ) diversity index, richness using Margaleff (d) and equitability by Pielou (J). Olyra taquara (Poaceae), Mikania sp. (Asteraceae), Cecropia sp. (Moraceae) and Miconia sp. (Melastomataceae) represented 83,5% of total seeds with mean density of 116,3 propagule/m2. The higher similarity in relation to species composition and density in seed rain was obtained between the closest fragments. All fragments showed low diversity (H ≤ 2.0), low equitability (J= 0,5084; Jtable= 1) and richness (d= 0,80), and low density of seed rain (< 500 propagules/m2), with high frequency of pioneer species. The highest richness was obtained in the small fragment, however with low value of equitability indicating that there were few species with many individuals. Wind dispersed species were observed in more intensity during October in the beginning, and zoochoric species dispersed their seeds in the end of rainy period. An increasing of species number was observed from the edge to fragment interior. Total biomass deposition was 4,9 t/ha which 69,4% were leaves, 14,2% branches, 6,4% reproductive material and 10% residual one. Sazonality was best expressed by biomass deposition in the end of the dry period, between September and November. Fragment size, distance among them and from edge were not significant, although F2 showed a trend to high value of total litterfall. Seed rain was considered a better bioindicator of fragmentation when compared to litterfall.