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Do practices of Sahelian smallholders farmers impact native agroforestry shrubs functioning?

This paper is available in a repository.
This paper is available in a repository.

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Preprint: policy unknown
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Postprint: policy unknown
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Published version: policy unknown

Abstract

During the last decades in Sahel, rainfall variability combined to land-use changes in order to supply increasing population (3%/year) with food has led to a drop in cereal production. An agroforestry systems made of Guiera senegalesis shrubs and millet crops is supposed to be sustainable in Niger because millet production increases visibly around shrubs. However, cutting practices could prevent the system from sustainability. Yearly in crop fields, before sowing and during the millet growth, shrubs are cut back and resprout immediately. Until now, the functional impacts on shrubs have yet not been addressed. To do so, we propose to compare leaf water potential and stomatal conductance between shrubs located in old fallow, young fallow, and crop fields. Leaf transpiration rate (E) and soil-to-leaf conductivity (KS-L) were deduced. Furthermore, leaf area, stem area, stem length were measured on shrubs. Soil water content and surface fluxes were monitored with an Eddy Correlation technics at plot scale. Results showed that leaf water potential decreases more in mature shrubs than in resprouts, in response to seasonal drought, suggesting that resprouts are less stressed. This is coherent with more soil water content measured in crop field than in fallow plots. In addition, it was observed that stomatal closure is coupled to leaves fall, which maintains viable water potential in mature shrubs during the dry season, but is decoupled in resprouts. Resprouts grow throughout the dry season thanks to KS-L twice higher than in mature shrubs, supporting thus their intensive regeneration. Consequently, resprouts induces a low but permanent rate of evapotranspiration at plot scale during the dry season. This adaptive strategy is probably common to many woody species that face both regular disturbance in periodic drought stress. However, the sustainability of such practices remains to be checked, especially the threshold of the resource exhaustion under repetitive yearly cutting.