Tree community variation in a tropical continental island according to slope aspect and human interference

ABSTRACT Associating description of unrecorded tropical tree community structure to sampling approaches that can help determine mechanisms behind floristic variation is important to further the comprehension of how plant species coexist at tropical forests. Thus, this study had the goals of (i) evaluating tree community structure on the continental island of Marambaia (23°4’37.09”S; 43°59’2.15”W) and (ii) testing the prediction that there are local scale changes in a tropical tree community structure between slopes facing different geographic orientation and with distinct human interference history. We established 60 (0.6 ha) sampling units in three different slope sites with distinct predominant geographic orientation and human interference. We sampled all woody trees with diameter at breast height (dbh) ≥ 5 cm. We found a total of 1.170 individuals representing 220 species, 120 genera and 50 families. The overall tree community structure and structural descriptors (abundance of individuals, basal area, species richness and diversity) varied extensively between the sites. The evidence presented here supports that local scale topography variations and human interference history can be important factors contributing to the known floristic heterogeneity of the Atlantic Rainforest. Future work on the study area should focus on disentangling effects from distinct causal factors over tree community variation and species occurrence

Pollen analysis of Holocene sediments from the Poço das Antas National Biological Reserve, Silva Jardim, Rio de Janeiro, Brazil

The Poço das Antas National Biological Reserve is located in Rio de Janeiro State, southeast Brazil. This paper presents information on past environmental characteristics of the area through pollen analysis. Two sedimentary columns were collected and five samples were selected for radiocarbon dating. The following ages of the columns from bottom to top were detected: column 1 - 1.20-1.16 m: 6080 ±40 years BP, 0.775-0.735 m: 4090 ±40 years BP, 0.385-0.345 m: 1880 ±80 years BP; column 2 - 1.22-1.18 m: 3520 ±40 years BP, 0.23-0.19 m: 1810 ±40 years BP. Three samples from column 1 and two samples from column 2 were selected for pollen analysis: 1.20 m, 0.77 m and 0.37 m of column1 and 1.22 m and 0.21 m of column 2. Chemical treatment followed standard methodology. The palynological analysis shows that around 6080 years BP the study area was dominated by a rain forest and from around 4090 years BP the vegetation changed to a fragmented forest, restricted to low hills and surrounded by an open area of grassland and pioneer plants, swamps and peat areas. The pollen assemblage of the samples 3520, 1880 and 1810 years BP suggest the permanence of this kind of vegetation between 4000 years BP and the actual.<br>A Reserva Biológica de Poço das Antas localiza-se no Estado do Rio de Janeiro, na região sudeste do Brasil. O presente estudo teve por objetivo fornecer informações a respeito de características ambientais pretéritas da área por meio de análises palinológicas. Foram coletadas duas colunas de sedimentos e cinco amostras foram selecionadas para datação pelo método de radiocarbono, revelando as seguintes idades, da base ao topo dos testemunhos: coluna 1 - 1,20-1,16 m: 6080 ± 40 anos AP, 0,775-0,735 m: 4090 ± 40 anos AP e 0,38-0,34 m: 1880 ± 80 anos AP; coluna 2 - 1,22-1,18 m: 3520 ± 40 anos AP e 0,23-0,19 m, 1810 ± 40 anos AP. Foram retiradas três amostras da coluna 1 e duas da coluna 2 para análise palinológica: 1,20 m, 0,77 e 0,37 m da coluna 1 e 1,22 m e 0,21 m da coluna 2. O tratamento químico foi baseado em metodologia padrão de preparação de amostras palinológicas. A análise palinológica indica que em torno de 6080 anos AP a área de estudo era dominada pela Floresta Ombrófila e que, por volta de 4090 anos AP, a vegetação tinha mudado para uma floresta fragmentada, restrita às baixas colinas circundadas por áreas de campo aberto, pantanosas e turfosas. A permanência desse tipo de vegetação entre 4000 anos AP e o atual é sugerida pelas amostras datadas de 3520,1880 e 1810 anos AP