Effects of habitat fragmentation on plant guild structure in the montane Atlantic forest of southeastern Brazil
Introduction
Forest fragmentation causes many physical and biological changes as a result of habitat loss and insularization (Lovejoy, Bierregaard, Rylands, Malcolm, Quintela, Harper, Brown, Powell, Powell, Schubart and Hays, 1986, Laurance, 1990). As forest landscapes become increasingly fragmented, populations of forest species are reduced, dispersal and migration patterns are interrupted, ecosystem inputs and outputs are altered, and previously isolated core habitats become exposed to external conditions, all of which result in a progressive erosion of biological diversity (Terborgh and Winter, 1980, Tilman, May, Lehman and Nowak, 1994). The creation of abrupt forest edges exposed to open habitats can severely modify local microclimatic conditions, increase tree mortality, and promote the establishment of non-forest species (Lovejoy, Bierregaard, Rylands, Malcolm, Quintela, Harper, Brown, Powell, Powell, Schubart and Hays, 1986, Kapos, 1989, Laurance, Ferreira, Rankin-de-Merona and Laurance, 1998a). Predictable shifts in the abundance and composition of plant species should also occur, in large part because of greater recruitment or lower mortality of light-dependent gap specialists along forest edges (Murcia, 1995, Laurance et al. 1998b).
Many consequences of forest fragmentation may have prolonged lag effects and require a sufficient “relaxation” period, with communities passing through a series of transitional states before final equilibrial conditions are reached (Simberloff, 1976, Tilman, May, Lehman and Nowak, 1994, Terborgh, Lopez, Tello, Yu and Bruni, 1997). Responses to insularization and habitat loss are thus best assessed in older fragments that have had adequate time to equilibrate (cf. Turner, Chua, Ong, Soong and Tan, 1996, Kellman, Tackaberry and Meave, 1997). The Brazilian Atlantic forest contains mainly older fragments (>50 years) and has one of the highest levels of plant and animal endemism of any continental tropical forest (Klein, 1980, Prance, 1982a, Prance, 1982a, Brown, 1987, Leitao Filho, 1994, Thomas, Carvalho, Garrison and Arbelaez, 1998). Of 127 woody species described for this region in the Flora Neotropica monographs, 68 (56%) are endemic (Mori et al., 1981), including 39 species in the Chrysobalanaceae alone (Prance, 1987). In addition to a large number of endemic plants, the Atlantic forest exhibits remarkably high plant diversity which may rival or exceed that of Amazonian forests (Silva and Leitao Filho, 1982, Mori, Boom, Carvalino and Santos, 1983, Martins, 1989, Peixoto and Gentry, 1990, Joly, Leitao Filho and Silva, 1991, Brown and Brown, 1992, Leitao Filho, 1994).
Following a history of severe and repeated anthropogenic disturbance since the sixteenth century, the Atlantic forest has been reduced to several thousand fragments accounting for only 8% of its pre-Columbian extent, which once encompassed some 12% of the Brazilian territory (SOS Mata Atlântica and INPE, 1993). Although this relentless fragmentation process has been curbed in recent decades, it has by no means been halted. For example, some 11% of the surviving Atlantic forest cover was lost between 1985 and 1990, leaving only 285,000 ha of forest remaining (SOS Mata Atlântica and INPE, 1993). While alarming from a conservation perspective, this intensely fragmented landscape with both old and new isolates provides an excellent opportunity for fragmentation studies (Brown and Brown, 1992, Viana and Tabanez, 1995, Tabarelli and Mantovani, 1997b).
This study evaluates the effects of habitat fragmentation on the structure and composition of woody plant guilds in Atlantic forest fragments that vary considerably in size (5–7900 ha). Guild structure is defined in terms of functional groups that relate to seed-dispersal mode, regeneration requirements, and height of mature individuals in the forest (sensu Giller, 1984). In particular, we determine whether and how the composition of different plant guilds varies with fragment size. We also consider the long-term viability of fragments remaining in the Brazilian Atlantic forest.
Section snippets
The forest fragments
This study examines the plant communities in five fairly well studied Atlantic montane forest fragments of the Atlantic Plateau within the Tietê River basin, State of São Paulo, southeastern Brazil. The fragments are located on the outskirts or just outside the urban perimeter of the city of São Paulo, ca. 100 km inland from the Atlantic coast (Fig. 1), at 700–850 m elevation (Table 1). All five fragments are relatively old (isolated for >50 years) and range from 5 to 7900 ha. They have
Effects of fragment size
The five fragments clearly differed in the proportions of species in guilds with varying light requirements at the seedling and sapling stage (Gadj=24.4, d.f.=4, P<0.001), growth form (Gadj=17.3, d.f.=4, P=0.001), and dispersal syndrome (Gadj=21.5, d.f.=4, P<0.001; G-tests for independence). The two smallest fragments had the highest proportions of shade-intolerant and canopy species dispersed by abiotic means (Fig. 2), and these guilds declined in importance as fragment size increased.
Floristic effects of fragment size
Our findings demonstrate that fragments of the montane Atlantic forest of southeastern Brazil differ in the guild structure of their plant assemblages, and that these changes are related to fragment size. Given the limited available data, we were unable to compare relative abundances of species in different guilds, but earlier studies (Aragaki and Mantovani, 1993, Tabarelli, 1994) suggest that our conclusions would have been strengthened had patterns of abundance been taken into account. Our
Acknowledgments
We thank the State of São Paulo Research Council (Fundação de Amparo á Pesquisa do Estado de São Paulo, FAPESP) for funding this study. We are enormously grateful to the Brazilian botanists who have contributed to our present understanding of the Atlantic forest flora. Herbarium staff at the São Paulo Botany Institute identified all plant vouchers. Phil Judge kindly prepared Fig. 1. W. F. Laurance, A. Carkeek, and an anonymous reviewer offered constructive criticisms on the manuscript.
References (83)
Edge effects in fragmented forestsimplications for conservation
Trends in Ecology and Evolution
(1995)Atlas pluviométrico do estado de São Paulo
(1972)- Aragaki, S., Mantovani, W., 1993. Estudos estruturais e taxonômicos de um trecho de remanescente de floresta no Parque...
- Baider, C., 1994. O banco de sementes e de plântulas na sucessão da Mata Atlântica. M.Sc. thesis, Instituto de...
- et al.
Flora arbórea da Serra da Cantareira (São Paulo)
Silvicultura em São Paulo
(1982) - et al.
Florı́stica e fitossociologia do estrato arbóreo de um trecho da Serra da Cantareira (Núcleo Pinheirinho)-SP
Revista do Instituto Florestal
(1992) - et al.
The biological dynamics of tropical rainforest fragments
BioScience
(1992) - et al.
Atlantic forest extinctions
Nature
(1996) Conclusions, synthesis and alternative hypotheses
- et al.
Habitat alteration and species loss in Brazilian forests
Leguminosae
Estrutura e colonização de clareiras em mata mesófila na Bacia de São Paulo, SP
Revista do Instituto Florestal
Projeto Olho Verde
Levantamento florı́stico e caráter sucessional das espécies arbustivo-arbóreas de uma floresta mesófila semidecı́dua no Municı́pio de Guarulhos, SP
Revista Brasileira de Biologia
Community structure and the niche
Posible papel de la vegetación secundária en la evolución de la flora tropical
Biotropica
Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory
American Naturalist
The importance of forest fragments to the maintenance of regional biodiversity in Costa Rica
Treefalls and tropical forest dynamics
The eternal external threat
O patrimônio florı́stico — the floristic heritage
A study of habitat fragmentation in southeastern Brazil using remote sensing and geographic information systems (GIS)
Forest Ecology and Management
Effects of isolation on the water status of forest patches in the Brazilian Amazon
Journal of Tropical Ecology
Preservation and management of biodiversity in fragmented landscapes in the Colombian Andes
Geographic patterning in tropical weed communities and early secondary successions
Biotropica
The consequences of prolonged fragmentationlessons from tropical gallery forests
Ecologia da flora e vegetação do Vale do Itajaı́
Sellowia
Comparative responses of five arboreal marsupials to tropical forest fragmentation
Journal of Mammalogy
Biomass collapse in Amazonian forest fragments
Science
Rain forest fragmentation and the dynamics of Amazonian tree communities
Ecology
Effects of forest fragmentation on recruitment patterns in Amazonian tree communities
Conservation Biology
Diversity of arboreal species in Atlantic rain forest
Anais da Academia Brasileira de Ciências
Ensaio para uma distribuição dos vegetais nos diversos grupos florı́sticos no estado de São Paulo
Boletim da Comissão Geográfica e Geológica de São Paulo
Edge and other effects of isolation on Amazon forest fragments
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