Biomes are defined by IBGE - Instituto Brasileiro de Geografia e Estatística (Brazilian Institute of Geography and Statistics) as "a set of life forms (vegetal and animal) consisting in contiguous types of vegetation that can be identified at a regional scale with similar geo-climatic conditions and a shared history of changes, resulting in a particular biological diversity”. According to the Mapa dos Biomas do Brasil (Biomes of Brazil Map), elaborated by IBGE and the Ministry of Environment, Brazil has 5 big biomes. The widest one is Amazon, that comprises 49.29% of Brazilian territory and an approximate area of 4,196,943 km². The smallest biome is Pantanal, with an approximate area of 150,355 km² or 1.76% of Brazil's territory. In Rio Grande do Sul, due to the diversity of climate, soils and relief, there is the formation of distinct ecosystems derived from two large biomes: Atlantic Forest and Pampa.
The domain of Atlantic Forest biome, i. e., its area of original vegetal coverage, that may be defined by the predominance of forest vegetation, extends for almost 37% of the State territory, occupying its northern half. At present, out of this percentage, only 7.5% remain in the State, although with a high grade of fragmentation. About 2,931,900 ha of these remaining areas are protected by law since 1993, forming the Atlantic Forest Biosphere Reserve of Rio Grande do Sul.
Regarding Pampa Biome, whose incidence in Brazil is restricted to Rio Grande do Sul, it occupies the southern half of the State or 63% of its territory. It is defined as grassland vegetation, predominantly in plains, that also extends by Uruguay and Argentina, and is characterized by the presence of a large diversity of fauna and flora still poorly studied. At present it is considered the second more threatened biome in the country, after the Atlantic Forest.
Source: IBGE and MMA. Mapa de Biomas do Brasil. 2004 (1:5,000,000)