The Brazilian Atlantic Forest: How much is left, and how is the remaining forest distributed? Implications for conservation
Introduction
Landscape structure parameters have been recognized as useful biodiversity surrogates, and are used in different steps of conservation planning (Williams et al., 2002, Lindenmayer et al., 2008). Some rules of thumb are employed within a landscape perspective, such as the conservation of large fragments with high structural connectivity, whether provided by corridors, stepping stones, or high permeability of the surrounding matrix (Umetsu and Pardini, 2007, Umetsu et al., 2008, Uezu et al., 2008, Fonseca et al., 2009, Pardini et al., 2009, Vieira et al., 2009); as well as targeting the preservation of as much as possible of all natural landscape heterogeneity (Forman and Collinge, 1997, Haila, 2002, Fischer et al., 2006, Lindenmayer et al., 2006, Metzger, 2006). Although they have some limitations, such as not considering how different species perceive features of the landscape (e.g., functional connectivity), landscape structure parameters can be particularly useful to establish general guidelines for conservation planning where broad-scale species inventories and biodiversity distribution patterns are still unavailable (Fairbanks et al., 2001; see Uehara-Prado et al., 2009 for a example of ecological indicators), which is the case for most tropical areas.
The Atlantic Forest was one of the largest rainforests of the Americas, originally covering around 150 million ha (Fig. 1), in highly heterogeneous environmental conditions. Its latitudinal range is around 29°, extending into tropical and subtropical regions. The wide longitudinal range is also important in producing differences in forest composition, because of the decreased rainfall away from the coasts. Coastal areas receive large amounts of rain year-round, reaching more than 4000 mm, while inland forests receive around 1000 mm/year (Câmara, 2003). These geographical characteristics, combined with the large altitudinal range, have favored high diversity and endemism, including more than 20,000 species of plants, 261 species of mammals, 688 species of birds, 200 species of reptiles, 280 species of amphibians, and many more species that still require scientific description (Goerck, 1997, Mittermeier et al., 1999, da Silva and Casteleti, 2003). The Atlantic Forest flora and fauna may include 1–8% of the world’s total species (Silva and Casteleti, 2003).
Most of the remaining Atlantic Forest exists in small fragments (<100 ha; Ranta et al., 1998) that are isolated from each other and are composed by second-growth forests in early to medium stages of succession (Viana et al., 1997, Metzger, 2000, Metzger et al., 2009). The few large fragments survived in locations where the steep terrain made human occupation particularly difficult (Silva et al., 2007). This present-day fragmentation has led to a large proportion of the forest’s vast biodiversity being threatened to extinction; for example more than 70% of the 199 endemic bird species are threatened or endangered (Parker et al., 1996, Stotz et al., 1996, Goerck, 1997).
In these heterogeneous and highly diverse forests, which still hold many still-unknown species (Lewinsohn and Prado, 2005), biodiversity inventories are complex, expensive and time-consuming (Gardner et al., 2008; but see Uehara-Prado et al., 2009). Despite the large amount of biological data generated in the Atlantic Forest region in recent decades (da Silva et al., 2004, da Silva and Casteleti, 2003), the lack of standardized inventory protocols and sampling efforts with poor spatial distribution have resulted in significant geographical data gaps, making it particularly difficult to use this information for conservation planning by the usual methods (see Margules and Pressey, 2000, Groves et al., 2002). At local scales, enough biological data is available for some areas to support conservation plans, but great difficulties arise in planning conservation actions for large regions. Moreover, most of the data are insufficient to properly support conservation planning, and thus, abiotic surrogates such as landscape structure parameters are in most cases the only alternative (Metzger et al., 2008). In this context, the amount of habitat and fragmentation, which are key factors for biodiversity conservation (Wilcox and Murphy, 1985, Fahrig, 2003), are important variables to be considered in landscape planning and management for biodiversity conservation.
Despite the potential of using landscape structure parameters in conservation planning, information on landscape structure in the Atlantic Forest is only available for small regions (<300,000 ha, Jorge and Garcia, 1997, Viana et al., 1997, Ranta et al., 1998). The only data available for the entire Atlantic Forest region is the percentage of the remaining forest, but even in this case there are huge discrepancies among the different methods employed (e.g., 7–8% of the forest remains according to SOS Mata Atlântica/INPE, 1993, 2000 and Galindo-Leal and Câmara, 2003; 10.6% according to SOS Mata Atlântica/INPE, 2008; and 27% according to IESB et al., 2007, Cruz and Vicens, in press).
We analyzed for the first time the spatial distribution of all the remaining Brazilian Atlantic Forest, in order to provide precise information about how much forest is left and how this forest is spatially arranged. We calculated parameters such as fragment size, amount of edge area, isolation, structural connectivity, and distance to conservation reserves of all existing fragments of the Brazilian Atlantic Forest region (ca. 245,000 fragments). These spatial analyses were performed on a multi-scale approach (Urban, 2005), in order to facilitate the biological interpretation of the landscape indices (within a perspective of ecologically scaled landscape indices; following Vos et al., 2001). This approach ensures a variety of biological behaviors, considering for example a wide range of sensitivity to gap-crossing abilities and to edge distance influences. Additionally, to refine our understanding about the Atlantic Forest spatial structure, considering its different regional contexts, we performed the same analyses dividing the region by biogeographical sub-regions (BSRs). The implications of the observed spatial patterns are discussed with regard to future conservation and restoration priorities for the entire Atlantic Forest in Brazil.
Section snippets
Study region and biogeographical sub-regions (BSRs)
The Atlantic Forest originally extended from 3°S to 31°S, and from 35°W to 60°W, covering 148,194,638 ha (Fig. 1), mainly extending along the Brazilian coast (92%), but also reaching into Paraguay (Cartes and Yanosky, 2003, Huang et al., 2007) and Argentina (Giraudo, 2003). The forest encompasses 17 Brazilian states, and is narrow in the north and wider in the south. It has complex boundaries with other types of formations such as the pampas in the south and the drier inland formations, such as
Forest cover
Of the total mapped area (139,584,893 ha), 15,719,337 ha of forest (11.26%) and 658,135 ha (0.47%) of restinga and mangrove vegetation (Table 3) still remain. Thus, 88.27% of the original Atlantic Forest has been lost, and only 11.73% of the original vegetation (16,377,472 ha) remains (Fig. 2 and Fig. 1S[a–g]). Considering the estimated commission and omission errors for the map analyzed (Table 1S; see Map quality section for details), we consider that the actual remaining vegetation might range
Discussion
Our results showed that: (i) there is more forest left than previously estimated; (ii) most fragments are very small, less than 50 ha (ca. 83% of the total number of fragments); (iii) much of the remaining forest is close to forest edges (ca. 45% <100 m of the edges), indicating that matrix influences may have strong effects on many forest ecological processes (Umetsu and Pardini, 2007, Umetsu et al., 2008, Uezu et al., 2008, Fonseca et al., 2009, Pardini et al., 2009, Vieira et al., 2009); (iv)
Conclusion
This report quantifies for the first time the extremely degraded state of the Atlantic Forest distribution, showing that most fragments cover less than <50 ha, almost half the remaining forest is <100 m from forest edges, and the present conservation network is insufficient to support the long-term survival of this rich and endangered tropical forest. Urgent conservation and restoration actions should be implemented to mitigate this situation, based on careful planning and with clear targets.
The
Acknowledgments
Our profound thanks to the SOS Mata Atlântica Foundation and the National Institute for Space Research (INPE) for allowing us to use their maps of remnants of the Atlantic Forest region. We also thank J.M.C. Silva and C.H.M. Casteleti for providing the boundaries of the BSRs analyzed in this study. Our appreciation to A. Uezu, C. Banks-Leite, C. Cornellius and two anonymous reviewers for commenting on earlier versions of this manuscript. Proof reading was done by J.W. Reid. MCR was granted a
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