Environmental heterogeneity and disturbance by humans control much of the tree species diversity of Atlantic montane forest fragments in SE Brazil

Abstract

The effects of human impact and environmental heterogeneity on the tree species diversity were assessed in 20 fragments of tropical montane seasonal forest in southeastern Brazil. Previous surveys of the tree community, soils and topography of the fragments provided the bulk of the data. The diversity parameters used were the means of species richness, Shannon diversity (H¢), and Pielou evenness (J¢) obtained from ''bootstrap'' sub-samplings of 1,000 trees. Morphometric variables obtained for the fragments included total, edge, and inner areas. Investigation forms were used to survey the history of human interventions and prepare an impacts matrix containing scores assigned to assess the extent, severity and duration of selected impacts. Scores for overall environmental impacts were obtained from the ordination scores produced by a multivariate analysis of the impacts matrix. A multivariate analysis of the standard deviations of soil variables was used to identify the variable which contributed most to soil heterogeneity. The same procedure was repeated for the variables related to topography and ground-water regime. The three species diversity parameters were related to the proportions of edges, the overall impacts scores, and the standard deviations of two selected soil and topographic variables. The species diversity in the fragments increased with increasing heterogeneity of both soil chemical properties and topographic features, and decreased with increasing proportion of forest edges. The evenness component of species diversity also increased with increasing severity of overall environmental impacts. This probably occurred because the 20 fragments did not include highly disturbed forests in the range and the intermediate disturbance effect on species diversity was therefore detected.

Honeydew foraging by birds in an Atlantic Forest fragment of Minas Gerais State, Brazil

“…The tropical climate of the region is characterized by rainy summers and dry winters. Mean annual precipitation and temperature at the base of the mountain range were 1.514-1.588 mm and 19,3-20,1 °C respectively, whereas at the upper montane area were 1.536-1.605 mm and 14,8-18,6 °C (Pereira et al 2007). Approximately 70% of the rains occur between November and February.…”

Composição e estrutura arbórea em floresta estacional semidecidual no Espinhaço Meridional (Serra do Cipó, MG)

“…Pereira et al (2007) Meguro et al (1996) encontraram valores de 4,6 e 0,8 para os mesmos índices, respectivamente. Estes altos valores podem ser explicados por fatores ambientais da região, tal como a maior precipitação ao longo do ano, fator relacionado positivamente à diversidade em florestas tropicais (Gentry 1988 (Brown & Lugo 1990;Oliveira-Filho et al 1997.…”

“…Parte desses estudos tem sido feita em remanescentes de Floresta Estacional Semidecidual, formação florestal fortemente atingida pela ação antrópica, cujos remanescentes são em sua maioria pequenos, esparsos e bastante perturbados (Pereira et al 2007;Pennington et al 2009). Os estudos florísticos e fitossociológicos realizados, além de somarem ao conhecimento da composição e da estrutura dessa formação (e.g., Oliveira-Filho et al 2004), fornecem informações valiosas para o desenvolvimento de projetos de manejo e recuperação de áreas impactadas.…”

Diferenciação Da Vegetação Arbórea De Três Setores De Um Remanescente Florestal Relacionada Ao Seu Histórico De Perturbações

“…A maior parte dos problemas ambientais que provocam mudanças na distribuição e abundância dos organismos é decorrente da fragmentação antrópica, que é considerada o principal agente de redução da biodiversidade (PEREIRA; OLIVEIRA FILHO; LEMOS FILHO, 2007;LAURANCE et al, 2011;HORNER et al, 2012). Sabe-se que, ao longo da sucessão, os processos ecológicos em florestas secundárias são fortemente influenciados por fatores de distúrbio, como frequência de queimadas, pastejo e outros fatores antrópicos (MARTINEZ-GARZA;HOWE, 2003;HORNER et al, 2012).…”