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After decades of drought in the Sahel, several studies have reported a ‘(re)greening’ of the area. However, most of these studies were based on large scale climatological or remotely sensed observations, with little or no ground truthing. The aim of this study was to assess the local perceptions of the distribution of socio‐economically important tree species in the Sub‐Sahel of Burkina Faso. Semi‐structured interviews were performed with 87 groups of informants from 20 villages belonging to three ethnic groups (Mossi, Fulani and Samo). Univariate and multivariate statistics were used to compare perceptions between the targeted ethnic groups. According to the locals, more than 80 per cent of the 90 listed species were declining, with over 40 per cent identified as threatened, including numerous plants of great economic value. Increasing species were mostly drought‐tolerant plants such as Balanites aegyptiaca. A few species were listed as locally extinct. Gender and age did not significantly affect local knowledge, whereas ethnicity did. The major causes of species decline were identified to be drought, deforestation and bushfires. In all ethnic groups, informants observed a southward shift in species distribution. Local perceptions suggest a general decline in woody vegetation. Thus, the alleged (re)greening in the Sahel might not have reversed the degradation of woody species in the area. Data derived from local ecological knowledge were consistent with that of many ecological studies, suggesting the reliability of people's knowledge for obtaining ecological data. Information from this study can be used as baseline for conservation of species identified as threatened. Copyright © 2011 John Wiley & Sons, Ltd.

In developing countries many people depend on woody resources for their livelihoods. Monitoring human impact on the populations of socioeconomically important species is therefore important for the conservation of vulnerable plants.In order to assess and compare the population structure and regeneration patterns of three multipurpose species, namely Acacia seyal Del., Balanites aegyptiaca Delile and Pterocarpus lucens Lepr. in four ethnic areas of the sub-Sahel of Burkina Faso (Samo, Gourmantché, Fulani and Mossi), we used the size-class distribution method (SCD) (Condit et al., 1998). Diameter at breast height (Dbh) of adult individuals of each species were sampled on 1000 m 2 (20 m  50 m) plots in each ethnic domain. Recorded Dbhs were distributed among eight size-classes of 5 cm intervals. For each species, the slope of the regression of the SCD was considered to be an indicator of the population structure. Seedlings and saplings were recorded on five nested 25 m 2 plots and fell into five height classes of 0Á5 m intervals. The target species had significant ( p < 0Á001) negative SCD slopes with an inverse J-shape distribution in all ethnic areas; indicating stable populations with good regeneration. Kruskal-Wallis test for the SCDs of A. seyal, B. aegyptiaca and P. lucens did not differ significantly among the ethnic areas ( p > 0Á1). This suggests that the dynamics of each of the three species is similar across ethnic domains and the subSahel. Data from P. lucens depicted an apparent stable population structure which contrasted with our field observations, perception of local people and previous studies.

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