[Este artigo, divulgado no www.usgs.org, dos Estados Unidos, mostra, a partir de estudo feito nas savanas do Senegal, a importância de não se confiar inteiramente em visualizações da vegetação feitas por sensoriamento remoto, para daí se concluir sobre o estado em que se encontra a cobertura vegetal]
O Sahel, onde se situa o Senegal, é uma região extremamente degradada (>3 milhões de km2) ao sul do Sahara, compreendendo ainda: Mauritânia, Mali, Burkina Faso, Níger, norte da Nigéria, Chade, Sudão, Etiópia, Eritreia, Djibouti e Somália. Há informações, obtidas de estudos sobre climas, de que as chuvas que antes caíam sobre essa região , provinham da América do Norte (EUA e Canadá) mas que mais recentemente a poluição existente nesses países evita que as massas de ar úmidas se desloquem para a África e "antecipa" a precipitação na América do Norte.
As fotos mostram que ocorreu um empobrecimento em espécies arbóreas, de 1983 a 2010. O aparecimento de arbustos é que influenciou o realce do verde das imagens de satélite (mostrado somente no artigo original).
O título do artigo é :
Vegetation impoverishment despite greening: A case study from central Senegal
- S.M. Herrmanna,
,
,
- G.G. Tappanb,
Acesso ao artigo completo:
Abstract
Recent remote sensing studies have documented a greening trend in the semi-arid Sahel and Sudan zones of West Africa since the early 1980s, which challenges the mainstream paradigm of irreversible land degradation in this region. What the greening trend means on the ground, however, has not yet been explored. This research focuses on a region in central Senegal to examine changes in woody vegetation abundance and composition in selected sites by means of a botanical inventory of woody vegetation species, repeat photography, and perceptions of local land users. Despite the greening, an impoverishment of the woody vegetation cover was observed in the studied sites, indicated by an overall reduction in woody species richness, a loss of large trees, an increasing dominance of shrubs, and a shift towards more arid-tolerant, Sahelian species since 1983. Thus, interpretation of the satellite-derived greening trend as an improvement or recovery is not always justified. The case of central Senegal represents only one of several possible pathways of greening throughout the region, all of which result in similar satellite-derived greening signals.
Highlights
► Decrease in species richness, despite increase in shrub cover in some sites. ► Decrease in large trees in both greening and control sites. ► Shift towards more aridity-tolerant species. ► Satellite derived greening signal cannot automatically be interpreted as improvement or recovery. ► Various pathways of greening possible throughout region.
Recent remote sensing studies have documented a greening trend in the semi-arid Sahel and Sudan zones of West Africa since the early 1980s, which challenges the mainstream paradigm of irreversible land degradation in this region. What the greening trend means on the ground, however, has not yet been explored. This research focuses on a region in central Senegal to examine changes in woody vegetation abundance and composition in selected sites by means of a botanical inventory of woody vegetation species, repeat photography, and perceptions of local land users. Despite the greening, an impoverishment of the woody vegetation cover was observed in the studied sites, indicated by an overall reduction in woody species richness, a loss of large trees, an increasing dominance of shrubs, and a shift towards more arid-tolerant, Sahelian species since 1983. Thus, interpretation of the satellite-derived greening trend as an improvement or recovery is not always justified. The case of central Senegal represents only one of several possible pathways of greening throughout the region, all of which result in similar satellite-derived greening signals.
Highlights
► Decrease in species richness, despite increase in shrub cover in some sites. ► Decrease in large trees in both greening and control sites. ► Shift towards more aridity-tolerant species. ► Satellite derived greening signal cannot automatically be interpreted as improvement or recovery. ► Various pathways of greening possible throughout region.
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