Tree functional group richness and landscape structure in a Brazilian tropical fragmented landscape

This study explores the relation between landscape structure and tree speci es richness in a tropical area suffering deforestation since the second hal f of the 19th century. Three different null hypotheses were tested: (1) the re is no relationship between landscape structure and tree species diversit y present in fragments because the process of fragmentation in these landsc apes is too recent to result in tree species extinction; (2) species charac teristics do not influence the relationship between tree richness and lands cape structure; (3) scale of analysis does not influence the relationship b etween tree richness and landscape structure. I studied 11 fragments of mes ophytic semideciduous forest occurring along the Jacare-Pepira river (south east Brazil). From a classified Thematic Mapper image, the landscape struct ure was quantified using parameters of fragment structure, forest arrangeme nt, landscape complexity, and landscape composition. To investigate the inf luence of scale over tree species richness, forest and landscape parameters were evaluated around the studied fragments for three different landscape extents. Each forest fragment community was divided into functional groups according to species dispersal capability and shade tolerance, to distingui sh possible differences in landscape perception. The relationships between landscape and community parameters were evaluated with regression and discr iminant analyses. Results showed significant relations between landscape pa rameters and species diversity. The nature of these relations changed accor ding to the group and to the landscape extent considered, supporting the vi ew that species perceive the landscape structure differently. The influence of landscape appears to be stronger for shade-tolerant, zoochorous, and ba rochorous species. Shade-tolerant species were particularly influenced by t he fragment structure (connectivity). Zoochorous species were particularly sensitive to landscape parameters at broad scales, whereas barochorous spec ies responded mainly to landscape structure at fine scales. These results a ttest to an influence of the present landscape structure on the tree commun ity, although the time lag of extinction occurring for long-lived trees may be longer than one century. Furthermore, results showed that boundary comp lexity and fragment connectivity were the most important parameters of land scape linked to the functional group richness and to total diversity, attes ting to the importance of the matrix structure in the relationships between landscape and fragmented communities.