Allometric models are necessary for estimating biomass in terrestrial ecosystems. Generalized allometric relationship exists for many tropical trees, but species- and region-specific models are often lacking. We developed species-specific allometric models to predict aboveground biomass for 11 native tree species of the Sudanian savannawoodlands. Diameters at the base and at breast height, with species means ranging respectively from 11 to 28 cm and 9 to 19 cm, and the height of the trees were used as predictor variables. Sampled trees spanned a wide range of sizes including the largest sizes these species can reach. As a response variable, the biomass of the trees was obtained through destructive sampling of 4 754 trees during wood harvesting. We used a stepwise multiple regression analysis with backward elimination procedure to develop models separately predicting, total biomass of the trees, stem biomass, and biomass of branches and twigs. All speciesspecific regression models relating biomass with measured tree dimensions were highly significant (p < 0.001). The biomass of branches and twigs was less predictable compared to stem biomass and total biomass, although their models required fewer predictors and predictor interactions. The best-fit equations for total above-ground biomass and stem biomass had R2 > 0.70, except for the Acacia species; for branches including twig biomass, R2-values varied from 0.749 for Anogeissus leiocarpa to 0.183 for Acacia macrostachya. The use of these equations in estimating available biomass will avoid destructive sampling, and aid in planning for sustainable use of these species. (Résumé d'auteur

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Background:The rapid growth of mobile phones in Ghana has opened up the possibility of delivering timely and useful weather and market information to farmers at costs lower than traditional agricultural extension services. In this paper, we assess the usefulness, constraints, and factors likely to influence farmers' decisions to patronize mobile phone-based weather and market information. Methods:We rely on primary data from 310 farmers in the Upper West Region, an understudied part of Ghana. We subject the data to three types of analysis. First, we model farmers' decision to patronize mobile phone-based weather and market information by estimating a binary logit model. Second, we use descriptive statistics and hypothesis testing to analyse the level of usefulness of mobile phone-based weather and market information. We disaggregate the analysis by sex, income status, and age group. Finally, we use qualitative analysis to summarize the constraints associated with the utilization of mobile phone-based weather and market information. Results:We find that contact with agricultural extension agents and farmer-to-farmer extension services significantly influences farmers' decision to patronize mobile phone-based weather and market information. Regardless of sex, income status, and age group, farmers generally rate mobile phone-based weather and market information as very useful. We identify inexact information, complex text messages, information that are too costly to implement, and poor infrastructure as the constraints to the utilization of mobile phone-based weather and market information. Conclusion:In order to improve the utilization of mobile phone-based weather and market information, disseminators of mobile phone-based information such as Esoko should constantly update and provide client-specific information. Improvements in mobile phone networks and related services will enhance the utilization of mobile phonebased weather and market information.

Background: Arid and semi-arid areas of West Africa are highly subject to climate change effects. This is combined to other drivers such as population growth and livestock number increase. To cope with such changing environment, endogenous adaptation strategies of poor local communities rely on the use of natural resources through empirical knowledge. Unfortunately, these knowledge and practices are insufficiently known to policy makers, and this hampers their consideration in the elaboration of adaptation strategies. A household survey was conducted in the Sillia village in northern Burkina Faso using semi-structured interviews. This study identified most used (preferred) species in this changing environment together with their ethnobotanical use value (VUET). Results:Overall, 86 ligneous species were listed in seven (7) use categories: human nutrition, fodder, fuel, traditional medicine, handicraft, construction and trade. From the 86 species, 11 appeared the most preferred by local population (VUET ≥ 6). Except Piliostigma reticulatum and Boscia senegalensis, all these species were part of the 21 very vulnerable species as revealed by the study. Tamarindus indica, Balanites aegyptiaca, Lannea microcarpa and Vitellaria paradoxa are the first most preferred species (VUET ≥ 7) and also most vulnerable (IV > 2.5). In this changing environment, Cassia sieberiana, Combretum micranthum, Balanites aegyptica have, for instance, become the main species used in traditional medicine replacing Ximenia americana, Coclospermum tinctorim, Maytenus senegalensis and Securidaca longepedunculata, formerly used for this need. Also, Piliostigma reticulatum is the main species used in farm lands to combat low soil fertility. Pterocarpus lucens and Adansonia digitata are the main fodder species both during dry and rainy seasons. Apart from the household surveys, vegetation survey was conducted on 96 plots in Sillia. The results showed that 25 species cited in the household surveys had locally disappeared, 22 were rare, 5 were abundant and the others were relatively abundant. Certain collection practices of given species in many use categories increase their vulnerability. Conclusion:This study documented preferred species in the adaptation strategies to changing environments and also assessed their vulnerability status under human influence; it is therefore of great use for designing sustainable management.