Water scarcity contributes to the poverty of around one-third of the world’s people. Despite many benefits, tree planting in dry regions is often discouraged by concerns that trees reduce water availability. Yet relevant studies from the tropics are scarce, and the impacts of intermediate tree cover remain unexplored. We developed and tested an optimum tree cover theory in which groundwater recharge is maximized at an intermediate tree density. Below this optimal tree density the benefits from any additional trees on water percolation exceed their extra water use, leading to increased groundwater recharge, while above the optimum the opposite occurs. Our results, based on groundwater budgets calibrated with measurements of drainage and transpiration in a cultivated woodland in West Africa, demonstrate that groundwater recharge was maximised at intermediate tree densities. In contrast to the prevailing view, we therefore find that moderate tree cover can increase groundwater recharge, and that tree planting and various tree management options can improve groundwater resources. We evaluate the necessary conditions for these results to hold and suggest that they are likely to be common in the seasonally dry tropics, offering potential for widespread tree establishment and increased benefits for hundreds of millions of people.

Accurate and timely maps of tree cover attributes are important tools for environmental research and natural resource management. We evaluate the utility of Landsat 8 for mapping tree canopy cover (TCC) and aboveground biomass (AGB) in a woodland landscape in Burkina Faso. Field data and WorldView-2 imagery were used to assemble the reference dataset. Spectral, texture, and phenology predictor variables were extracted from Landsat 8 imagery and used as input to Random Forest (RF) models. RF models based on multi-temporal and single date imagery were compared to determine the influence of phenology predictor variables. The effect of reducing the number of predictor variables on the RF predictions was also investigated. The model error was assessed using 10-fold cross ). This mapping approach is based on freely available Landsat 8 data and relatively simple analytical methods, and is therefore applicable in woodland areas where sufficient reference data are available.

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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.

BackgroundGenetic diversity provides the capacity for plants to meet changing environments. It is fundamentally important in crop improvement. Fifty-nine local maize lines developed at INERA and 41 exotic (temperate and tropical) inbred lines were characterized using 1057 SNP markers to (1) analyse the genetic diversity in a diverse set of maize inbred lines; (2) determine the level of genetic diversity in INERA inbred lines and patterns of relationships of these inbred lines developed from two sources; and (3) examine the genetic differences between local and exotic germplasms.ResultsRoger’s genetic distance for about 64% of the pairs of lines fell between 0.300 and 0.400. Sixty one per cent of the pairs of lines also showed relative kinship values of zero. Model-based population structure analysis and principal component analysis revealed the presence of 5 groups that agree, to some extent, with the origin of the germplasm. There was genetic diversity among INERA inbred lines, which were genetically less closely related and showed a low level of heterozygosity. These lines could be divided into 3 major distinct groups and a mixed group consistent with the source population of the lines. Pairwise comparisons between local and exotic germplasms showed that the temperate and some IITA lines were differentiated from INERA lines. There appeared to be substantial levels of genetic variation between local and exotic germplasms as revealed by missing and unique alleles.ConclusionsAllelic frequency differences observed between the germplasms, together with unique alleles identified within each germplasm, shows the potential for a mutual improvement between the sets of germplasm. The results from this study will be useful to breeders in designing inbred-hybrid breeding programs, association mapping population studies and marker assisted breeding.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-014-0127-2) contains supplementary material, which is available to authorized users.

Effect of shading by baobab (Adansonia digitata) and néré (Parkia biglobosa) on yields of millet (Pennisetum glaucum) and taro (Colocasia esculenta) in parkland systems in Burkina Faso, West Africa Abstract An experiment was conducted in Nobéré, Burkina Faso to assess the effect of shade of two indigenous fruit trees, Adansonia digitata (Baobab) and Parkia biglobosa (Néré), on a shade-tolerant crop called taro (Colocasia esculenta) in comparison with millet (Pennisetum glaucum) a shade-intolerant crop. Photosynthetically active radiation (PAR) and performance of crops under trees and in the open field were assessed during three cropping seasons. Millet performed better under baobab (806.1 ± 121.48 kg ha -1 ) compared to the control plot (595.8 ± 83.43 kg ha -1 ) and néré (320.2 ± 59.91 kg ha -1 ). In contrast, the yield of taro was higher under néré (4124.0 ± 469.05 kg ha -1 ) compared to the control plot (2336.9 ± 617.04 kg ha -1 ) and baobab (2738.3 ± 595.61 kg ha -1 ). There was a strong relationship between the amount of PAR intercepted by trees and crop yields under trees. As PAR decreased the yield of millet decreased whereas the yield of taro increased. Hence, it was concluded that parkland productivity could be enhanced by cropping taro under néré where light reduction was 83, 56 and 18% in zones A, B and C, respectively. An efficient association of baobab with crops could be the production of taro in zone A and millet in zones B and C where PAR reduction was 62, 38 and 15%, respectively.

In the current debate on the role of increase soil carbon in addressing both climate change and food security, there is consensus that farmed lands have the higher potential provided the best management practices are implemented. In the Sahel where farms usually have few sparse old trees with declining soil fertility, there is an ongoing re-greening process with increases in tree cover for which there is still a dearth of quantified information on its impacts on soil properties. This research aimed at filling that gap. We sampled soil using a concentric zone design around individual trees of dominant species and at different soil depths (0-10, 10-30, 30-50 and 50-70 cm) in four Sahelian countries: Burkina Faso, Mali, Niger and Senegal. The results showed increase total carbon content of the top 0-10 cm soil, generally with high sand content ([ 70%), ranged from 0.16 to 0.44% (mean 0.23%). Under trees it was a factor 1.04-1.47 higher than away from trees. Different tree species thrived in different ecological niches and had different impacts on soil properties, highlighting the need for site and species matching in restoration activities. These results suggest that increase vegetation cover in the Sahel is associated with an increase in soil total carbon and this trend is more pronounced on sandy soils.