Deforestation to establish monocrops in the tropics is causing massive reductions in ecosystem C stocks. Amazonia is a principal target of this process, owing to the expansion of the agribusiness frontier throughout the transition with the Cerrado biome, the zone known as the "Arc of Deforestation". In this vast contact region between the two largest South American biomes, conversion of primary forest to soybean and pasture systems has led to the deforestation of nearly five million hectares since 1980. Despite this, we lack precise understanding of the effects of land use on ecosystem C stocks and pools in this region. Addressing this knowledge gap is crucial to improve predictions and fit models for different land use scenarios in Amazonia. To reduce uncertainty regarding the magnitude of the impacts of deforestation on the C cycle, we evaluated ecosystem C stocks in contrasting land-use systems across a topographically, climatically, and edaphically near-homogeneous landscape in southern Amazonia. We investigated the soil, litter, fine root and aboveground biomass (AGB) C stocks of soybean plantations and compared them to those of remnant native forests and rubber plantations; the latter is considered a priori as a cropping system with low impact on the C cycle. We found that the conversion of native forest to soybean plantation caused a 130.5 Mg C ha-1 loss, about threefold higher than the loss when forest is converted to rubber plantations, 48.5 Mg C ha-1. While 30-year old rubber plantations had recovered 84% of forest carbon stocks, all plantation types induced sustained losses of at least onethird of the original soil carbon. Fine root allocation changed sharply in the two crops following conversion, indicating an alteration in plant nutrient dynamics. Our results show that perennial and annual monocrops have very different impacts on the C cycle, which need to be accounted for in carbon-climate models as well as in public policies regulating land use in Amazonia. Our results show that while silviculture has the potential to restore most of the above-ground C stocks of previously forested areas, neither silviculture nor conventional agriculture may ever restore Amazon soil C stocks once they become vulnerable and oxidized after deforestation. If such conversion-driven soil carbon losses were scaled across the Amazon they would induce a cumulative loss of more than 5 Pg in soil carbon by 2050.
Deforestation may have effects on the hydrological cycle, directly reflecting in the rainfall rates. Therefore, studies pointing out evidence of climate changes caused by deforestation are extremely important, because they help understanding the way how these changes are related to forms of using and occupying the territory, as well as to the way how information obtained can to be useful for mitigating their effects. In this context, this paper aimed to analyze rainfall variations occurring in the municipality of Colíder, Mato Grosso, southern Amazon,Brazil, within a temporal scale of 28 years (daily data), correlating them to the regional and local deforestation patterns by determining Spearman's ρ coefficient. Annual rainfall presented a large variation, with a minimum of 1,296 mm in 1987 and a maximum of 2,492.8 mm in 1990. The rainy season was concentrated between October and April, and the driest period was within June and August. Spearman's coefficient pointed out negative correlations between regional and local deforestation and local rainfall, showing that the larger the deforested area, the lower the rainfall rate observed. Keywords: Rainfall variability, Gamma probability, Vegetation removal, Arc of deforestation. RESUMO: PRECIPITAÇÃO PLUVIOMÉTRICA E DESMATAMENTO NO MUNICÍPIO DE COLÍDER, SUL DA AMAZÔNIAA destruição das florestas pode ter efeitos no ciclo hidrológico, refletindo diretamente nas taxas de precipitação. Desta maneira, estudos que apontem indícios de alterações climáticas ocasionadas pelo desmatamento são extremamente importantes, pois facilitam a compreensão de como estas mudanças estão relacionadas às formas de uso e ocupação do território e de que modo as informações obtidas serão úteis na mitigação dessas mudanças. Neste contexto, o objetivo deste artigo foi analisar as variações pluviométricas ocorridas no município de Colíder (MT), sul da Amazônia, em uma escala temporal de 28 anos (dados diários), correlacionando-as aos padrões regionais e locais de desmatamento por meio da determinação do coeficiente ρ de Spearman. A precipitação anual apresentou grande variação, com mínima de 1.296 mm em 1987, e máxima de 2.492,8 mm em 1990. O período chuvoso concentrou-se entre outubro e abril, e o período mais seco foi entre junho e agosto. O coeficiente de Spearman apontou correlações negativas entre o desmatamento regional e local com a precipitação local, evidenciando que quanto maior for a área desmatada, menor será a taxa pluviométrica observada. Palavras-chave: Variabilidade pluviométrica, Probabilidade Gama, Supressão da vegetação, Arco do desmatamento.
ResumoO processo de colonização da Amazônia mato-grossense foi marcado pela ocupação e uso desordenado do território. Os colonos, oriundos principalmente da região Sul, trouxeram consigo várias técnicas de cultivo e modelos de exploração até então não praticados na região, estabelecendo, desta maneira, um novo cenário socioeconômico e ambiental. As faces desse novo sistema de produção agrícola constituem-se como motivo de muita discussão no meio científi co. Com base neste cenário, objetivou-se realizar um referencial bibliográfi co dessas interfaces considerando-se os tipos de exploração, a origem dos agricultores e os possíveis impactos ambientais para a referida região. AbstractThe process of colonization of the Amazon Forest in the state of Mato Grosso was characterized by disorderly occupation and use of territory. The settlers, coming mainly from the south of Brazil, bring with them a lot of farming techniques and exploration models which were unkown in this region, establishing a new environmental and socioeconomic scenario. The implications of this new system of agricultural production have been largely discussed in the academy. Based in this scenery, we aimed to raise bibliographical references of these implications, taking in account the kinds of exploration, the origin of the farmers and the environmental impacts for the region.
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