Southern Brazil is a transitional zone between tropical and temperate climates and the natural vegetation is a mosaic of grassland, shrubland and different forest types (Hueck 1953, 1966, Klein 1978, 1979, 1984, Rambo 1953, 1956b, Por 1992, Boldrini 1997, Pillar and Quadros 1997, Overbeck at al. 2007). As regards grassland vegetation, on the highland plateau in Paraná, Santa Catarina and Rio Grande do Sul states, grasslands form mosaics with Araucaria forest (Figs. 1, 2). The grasslands of the southern and western parts of Rio Grande do Sul State are often included in the same type of grasslands that extend into Argentina and Uruguay (Burkart, 1975; Soriano et al., 1992).
Boldrini (1997) estimated a total number of 3,000 grassland plant species in Rio Grande do Sul State alone. The grassland vegetation is often regionally differentiated into "campo limpo" ("clean grassland"), which contains a predominance of herbs of the Poaceae, Cyperaceae and Asteraceae family, and "campo sujo" ("dirty grassland"), which in addition to grasses and sedges contains shrubs, primary of the families Asteraceae (Baccharis spp.) and
Apiaceae (e.g. Eryngium spp.) (Klein, 1978). Boldrini (1997) describes physiognomic regions of Campos vegetation in Rio Grande do Sul State, considering local floristic variations associated with climate, topographic variation and soil heterogeneity. However, a good portion of the variation in grassland physiognomy and in the composition of the dominant species seems to be determined by grazing and fire regimes (Pillar and Quadros, 1997). Under low grazing intensity tall grasses dominate (Andropogon spp., Aristida spp., Schizachyrium spp.) mixed with shrubs such as Baccharis spp., Vernonia spp. (Asteraceae) and Eryngium horridum (Apiaceae).
Campos de altitude (high elevation grasslands) occur on mountains, at elevations above 1600 m in southern Brazil and above 1800 m in southeastern Brazil. This grassland contains species of the Poaceae and Cyperaceae families, but also includes small shrubs of Melastomataceae, Ericaceae, Eriocaulaceae, Asteraceae and Verbenaceae (Safford 1999a, 1999b). Campos de altitude is rich in endemic species and occurs on several mountain peaks in S and SE Brazil (Ferrao and Soares 1989).
The present-day grassland vegetation is highly affected by different agricultural land-use practices and more recently by large-scale afforestation by exotic species, (mainly Pinus and Eucalyptus). Until 1996, an estimated decrease of 25% in the total area of natural grasslands has occurred due to a strong expansion of agricultural activities (Nabinger et al. 2000). More recent mapping of natural vegetation remnants in the south and west of Rio Grande do Sul State alone (MMA 2007) indicates ca. 50% loss of natural grassland habitats by the year 2002.
The climate of the southern highland region is defined as subtropical warm temperate and humid without marked dry periods (Nimer 1989). The southern highlands form an orographic barrier for southeasterly to northeasterly winds. As a consequence, the rainfall is high with an average annual rainfall of over 2000 mm. The mean annual temperature is 14.5 °C. The lowest recorded temperature for the eastern highland is -6.5 °C (Nimer 1989). In general, the climate of southern Brazil is influenced by the South Atlantic anticyclone, a semi-permanent high-pressure system which transports moist tropical air masses over the continent from easterly and northeasterly directions during the whole year. Disturbances are related to polar cold fronts, which when meeting the tropical air masses, produce strong rainfall in southern Brazil (Nimer 1989, Hastenrath 1991). Higher rainfall in southern Brazil is also related to El Niño events (Martin et al. 1993, Ratisbona 1976).
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