ABSTRACT
A AMAZÕNIA está entrando em uma era de rápidas mudanças impulsionadas pela previsão de asfaltamento de rodovias que estimularão a expansão da fronteira agrícola e de exploração madeireira. O declínio do custo de transporte tem importantes implicações para a biodiversidade, emissão de gases que contribuem para o efeito estufa e prosperidade da sociedade da Amazônia a longo prazo. Para analisar esse contexto, foi desenvolvido um modelo de simulação de desmatamento na bacia Amazônica, sensível a diferentes cenários de políticas públicas frente à expansão da infra-estrutura de transporte pela região. Resultados do modelo indicam que, dentro de um cenário pessimista, o desmatamento projetado pode eliminar, até meados deste século, 40 por cento dos atuais 5,4 milhões de km² de florestas da Amazônia, liberando o equivalente a 32 Pg (10(9) toneladas) de carbono para atmosfera. A modelagem de cenários alternativos aponta que a expansão de uma rede de áreas protegidas, efetivamente implementadas, poderia reduzir em até 1/3 as perdas florestais projetadas. Contudo, outras medidas de conservação são ainda necessárias para se manter a integridade funcional das paisagens e bacias hidrográficas amazônicas. Atuais experimentos em conservação florestal em propriedades privadas, mercados de serviços ambientais e zoneamento agro-ecológico devem ser refinados e multiplicados a fim de se buscar uma conservação extensiva.
Subject(s)
Amazonian Ecosystem , Conservation of Natural ResourcesABSTRACT
The total area and annual rate of native vegetation clearing is greatest in the Cerrado region followed by the Brazilian states of Par , Mato Grosso, Maranhao and Rond"nia. Amazonian forest clearing proceeds most quickly where abundant natural resources (wood or land) are accessible by roads and close to markets. These regions are concentrated along the eastern and southern flanks of Amazonia, particularly in eastern Par , Cuiab and Rond"nia. There are still large discrepancies in estimates of annual deforestation; Landsat (Thematic Mapper-based) mapping of deforestation in the closed-canopy forests of Amazonia has not include non-Brazilian countries and is incomplete for the cerrado biome. Amazonian deforestation was last mapped in 1994. Current estimates of Amazonian forest clearing do not include most of the forests that are effected by logging each year, which is an area (about 7,000 Km2yr-1) more than half the size of the area of annual deforestation. Logging changes forest structure and increases forest flammability. The intensity of logging ranges from 1- to 100-species harvest, and averages 20 m3 of wood harvested per hectare. Logging may increase dramatically in the coming years. Fire affects large, but difficult to measure, areas of pastureland, logged forests, secondary forests and primary forests. Forest ground fires are particularly difficult to map from satellite data. Fire is more frequent where forest clearing is taking place, and where seasonal drough is most severe. The destiny of Amazonian forest land cleared for crops and cattle pasture is complex, and highly variable regionally. Areal estimates are needed for managed pasture, degraded pasture, cropland and secondary forests, for these ecosystems are functionally distinct. Most forest clearing is for pasture establishment, followed by shifting cultivation. Cattle pasture is the logical land-use for both small-scale and large-scale rural Amazonians because cattle are easily sold or traded, and they maintain their value during inflation. Cattle pastures help secure land claims and increase land value. In the Cerrado, there has been a shift from extesive cattle grazing of natural savannas to pastures planted with African forage grasses; mechanized soy bean production is the second most extensive land-use. Pastures are the most important land-cover for the LBA (Large-Scale Biosphere-Atmosphere experiment in Amazonia) science campaign. Brazilian Amazonia experiences reduced rainfall...