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Communication incl. Poster: BibTeX citation key:  Hiernauxc
Hiernaux, P., Mougin, E., Trichon, V. & Le Dantec, V. 2009. Sahel vegetation vulnerability to droughts, grazing and clearing for cropping: lessons from long term monitoring in Gourma (Mali) and Fakara (Niger). Work presented at Third International AMMA Conference, July 20—24, at Ouagadougou, Burkina Faso.
Added by: Devic 2009-10-08 09:48:14    Last Edited by: roussot 2009-10-16 16:32:31
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Categories: Environment and Climate Monitoring, Society-Environment-Climate interactions
Keywords: Vegetation
Creators: Hiernaux, Le Dantec, Mougin, Trichon
Publisher: African Monsoon Multidisciplinary Analyses (Ouagadougou, Burkina Faso)
Collection: Third International AMMA Conference

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Abstract
The whole Sahel bioclimatic zone experienced low rainfall condition starting the late 1960’s with severe droughts in 1972-73 and 1983-84. These climate events occurred in a context of persistent increased pressure on resources following steady rural population increase in spite of out migrations fluxes.
The AMMA project took over existing vegetation monitoring systems with 25 rangeland sites monitored from 1984 to 2006 in Gourma (Mali) and 71 cropland, fallow and rangeland sites monitored from 1994 to 2006 in Fakara (Niger).
In Fakara there is an overall decreasing trend in site yields by 5% annually from 1994 to 2006 that is not explained by variations in rainfall. Causes are likely to be multiple which might include changes in land use, decline of soil fertility and increased grazing pressure. In Gourma, the inter-annual variability of herbaceous yield of rangelands increases as climate gets dryer. In the long term, heavy grazing promote either long cycle annuals refused by livestock or else short cycle good quality feed species. Year to year changes in species composition are abrupt. However, some decadal trends in species composition are identified, with fast pioneer phases and slow diversification trends. Woody plant populations in Gourma were struck by the 1983-84 droughts irrespective of their edaphic situation, location along the bioclimatic gradient and grazing intensity. Although rainfall remained low, active recruitment in successive cohorts occurred in most sites except some of the shallow soil sites. In Fakara, the dynamics of woody plant cover is narrowly related to land use changes with an historical decline in cover and density since the 1950’s.
Throughout Sahel the herbaceous layers largely varies in annual production and species composition. There is however a large resilience to rainfall variations on sandy soil. On shallow and fine textured soils, herbaceous and woody vegetation could be durably affected.
Last Edited by: roussot