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CENTRES OF PLANT DIVERSITY AND ENDEMISM.
IV. Mata Atlântica
The narrow Mata Atlântica formation originally extended from Brazil's north-eastern tip near Cabo de São Roque in Rio Grande do Norte State to Torres in Rio Grande do Sul, the country's southernmost state. Biologically the Mata Atlântica is often divided into northern, central and southern portions. The northern part extends from Rio Grande do Norte to Bahia, the central part from Espírito Santo to São Paulo and the southern part from southern São Paulo to north-eastern Rio Grande do Sul. In addition to the coastal forest, much of the drainage of the Paraná River is floristically a part of the Mata Atlântica, extending from about 20°S in southern Minas Gerais to 30°S in central Rio Grande do Sul, and also including most of Paraguay east of the Paraguay River and Argentina's north-easternmost province of Misiones. As thus defined the Mata Atlântica also includes the upland region of Paraná and adjacent states where Araucaria forest is the dominant vegetation.
Whereas most of the Mata Atlântica region has a relatively low annual rainfall, mostly below 2000 mm, the dry season is usually relatively weak. As a result annual precipitation as low as 1400 mm can support physiognomically and floristically typical tropical moist forest, as at Linhares in Espírito Santo (Peixoto and Gentry 1990). The tropical portion of the Mata Atlântica is also peculiar in its latitudinal extent, with speciesrich forest crossing the Tropic of Capricorn and reaching at least 24°S latitude. Elsewhere in the world, tropical forests generally become less diverse poleward from 12° latitude (Gentry 1990b). South of São Paulo and in the Paraguay portion of the Mata Atlântica, species richness drops off abruptly, although the forests are still physiognomically tropical and endemism may remain high. For example, the most diverse Paraguayan forest at Mbaracayú (24°42'S) has only 85 species over 2.5 cm dbh in 0.1 ha (Keel, Gentry and Spinzi 1993). However, a local Florula (Barros et al. 1991) from Cardoso Island south of 25°S in extreme southern São Paulo State has a respectable 986 species. Rough montane topography and shallow soils, landslides due to high rainfall, along with natural forest dynamics and in the south the occurrence of frost (minimum -4°C) in 1-5 days each year, result in a mosaic of successional stages and consequently a highly variable species composition (Mantovani 1990).
The Mata Atlântica forests are very diverse botanically, with an estimated 13,000 angiosperm species, accounting for c. 16% of the neotropical flora, in a relatively small area (Gentry 1982a). At the level of local plant communities, the Mata Atlântica forests are also unusually diverse, presumably primarily because of the relatively weak dry season characterizing much of the region. Indeed 0.1-ha samples of the forests of Espírito Santo and Rio de Janeiro states, where precipitation is only 1400-1500 mm, have 160-200 species of plants over 2.5 cm dbh, as many as in all but the richest of Amazonian forests (Peixoto and Gentry 1990, and original data).
There are some conspicuous floristic differences between the Mata Atlântica and Amazonia. Most striking is the prevalence here of Myrtaceae, which generally replaces Leguminosae as the most prevalent woody family (Peixoto and Gentry 1990). Monimiaceae is also much represented when compared to Amazonia. On the other hand, other prevalent Amazonian families are poorly represented, such as Myristicaceae, Palmae, Moraceae, Meliaceae, Chrysobalanaceae and Lecythidaceae. Bignoniaceae is the dominant liana family, just as elsewhere in the lowland neotropics, but Hippocrateaceae is better represented than elsewhere, edging out Leguminosae as the second most prevalent liana family. On the other hand, Connaraceae and Dilleniaceae are generally more poorly represented among lianas than in Amazonia. Orchids are especially prevalent in many Mata Atlântica forests; for example Orchidaceae is by far the largest family on Cardoso Island, with 118 species, 12% of the entire flora (Barros et al. 1991).
Overall endemism is very high in the Mata Atlântica, with an estimated 9400 angiosperm species endemic (Gentry 1992d). This 73% regional endemism is second only to Amazonia among the neotropical phytogeographic regions (Gentry 1992d). As usual the endemism is concentrated in epiphytes and other herbaceous taxa. An estimated 67% of the Mata Atlântica canopy taxa are endemic to the region (53% of the trees fide Mori and Boom 1981), whereas an astounding 86% of the Mata Atlântica taxa of principally herbaceous and shrubby families are apparently endemic, a higher figure than for any other neotropical phytogeographic region (Gentry 1982a).
Local endemism appears to be equally high, but few actual data are available. Although many species are wideranging, there appears to be a disproportionate number of local endemics, especially in such specialized habitats as the coastal "restingas". Endemism may be concentrated in Rio de Janeiro State, although this could partially reflect collection artefact; for example, 36 species are endemic to its coastal restingas, with 11 endemic to the Cabo Frio region.
Perhaps the two most economically important plants of coastal Brazil are the legume timber trees Caesalpinia echinata (Brazil-wood) and Dalbergia nigra (Brazilian rosewood), the latter once considered Brazil's most valuable wood. Both have been over-exploited and are now very rare. Also very important economically are several Bignoniaceae timber trees, including Paratecoma peroba, a locally endemic genus and species of the Doce River Valley, which was once the most important timber of Rio de Janeiro but is now nearly extinct (Record and Hess 1940; Gentry 1992b). A similar fate may be now befalling Tabebuia heptaphylla in eastern Paraguay, where it is the preferred timber species. Rhizomes from the tree fern Dicksonia sellowiana are used as substrate for the cultivation of ornamentals. Some widely consumed fruits like Myrciaria cauliflora are also native to the region. Nevertheless, it is curious that the economically valuable plants singled out in the CPD Data Sheets on the Mata Atlântica are mostly timber trees, whereas in other regions edible fruits and medicinal plants are often emphasized. This might be happenstance or reflect some kind of real cultural or biological difference.
The Atlantic forest region is the agricultural and industrial heart of Brazil, with c. 43% of the country's population. In north-eastern and south-eastern Brazil much of the conversion was completed with settlement by the end of the 19th century, although in the temperate southern area devastation has accelerated since the 1970s. The central Atlantic region (southern Bahia and northern Espírito Santo) mostly has been converted since c. 1965 with the opening of new access routes (Brown and Brown 1992).
From the viewpoint of plant conservation, the Mata Atlântica is one of the world's most critical regions; this area featured prominently as one of Myers' (1988) extinction hot spots. Of the original area of forest of c. 1.2 million km, well over 1 million km had been deforested by 1990. Estimates of remaining forest range from 12% (Brown and Brown 1992) to 2-5% (IUCN and WWF 1982), most of which is highly fragmented.
Almost 31,000 km² of the remaining forest, 2.5% of the original area, are variously protected in many National Parks and equivalent reserves, mostly in the southern part of the Mata Atlântica in the states São Paulo (11,540 km²) and Paraná (5160 km²) (Brown and Brown 1992). The Fundaço SOS Mata Atlântica (SOS Atlantic Forest Foundation) was founded in 1986 to stimulate, assist and coordinate efforts to conserve the remaining important sites of the region (Collins 1990).
Centres of Plant Diversity and Endemism
a. NORTHERN REGION
|S.A. Regional Overviews|
|I. Caribbean (of South America)||V. Interior dry and mesic forests|
|II. Guayana Highlands||VI. Andes|
|III. Amazonia||VII. Pacific Coast|
|IV. Return to Top This Region||VIII. Southern Cone|
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