In tropical West Africa, distribution patterns of forest islands in savannas are influenced by fires which occur regularly in the grass stratum. Along continuous forest–savanna transects in the Comoé National Park, the change in the amount and composition of non-woody phytomass was investigated from savanna to forest interior. This was correlated with the cover of vegetation strata above, soil depth, and the occurrence of seasonal surface fires. Phytomass mainly consisted of leaf litter in the forests (about 400 g m−2 at the end of the rainy season, and about 600 g m−2 at the end of the dry season) and of grasses in the savanna (about 900 g m−2). Low grass biomass appeared to be primarily the result of suppression by competing woody species and not of shallow soil. The occurrence of early dry-season fires seemed to be determined mainly by the amount of grass biomass as fuel because fires occurred in almost all savanna plots while forest sites remained unaffected. However, late dry-season fires will encounter higher amounts of leaf litter raising fire probability in forests. Due to the importance of the amount of combustible phytomass, fire probability and intensity might increase with annual precipitation in both savanna and forest.

Mutualistic biotic interactions as among flowering plants and their animal pollinators are a key component of biodiversity. Pollination, especially by insects, is a key element in ecosystem functioning, and hence constitutes an ecosystem service of global importance. Not only sexual reproduction of plants is ensured, but also yields are stabilized and genetic variability of crops is maintained, counteracting inbreeding depression and facilitating system resilience. While experiencing rapid environmental change, there is an increased demand for food and income security, especially in sub-Saharan communities, which are highly dependent on small scale agriculture. By combining exclusion experiments, pollinator surveys and field manipulations, this study for the first time quantifies the contribution of bee pollinators to smallholders’ production of the major cash crops, cotton and sesame, in Burkina Faso. Pollination by honeybees and wild bees significantly increased yield quantity and quality on average up to 62%, while exclusion of pollinators caused an average yield gap of 37% in cotton and 59% in sesame. Self-pollination revealed inbreeding depression effects on fruit set and low germination rates in the F1-generation. Our results highlight potential negative consequences of any pollinator decline, provoking risks to agriculture and compromising crop yields in sub-Saharan West Africa.

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The international, interdisciplinary biodiversity research project BIOTA AFRICA initiated a standardized biodiversity monitoring network along climatic gradients across the African continent. Due to an identified lack of adequate monitoring designs, BIOTA AFRICA developed and implemented the standardized BIOTA Biodiversity Observatories, that meet the following criteria (a) enable long-term monitoring of biodiversity, potential driving factors, and relevant indicators with adequate spatial and temporal resolution, (b) facilitate comparability of data generated within different ecosystems, (c) allow integration of many disciplines, (d) allow spatial up-scaling, and (e) be applicable within a network approach. A BIOTA Observatory encompasses an area of 1 km(2) and is subdivided into 100 1-ha plots. For meeting the needs of sampling of different organism groups, the hectare plot is again subdivided into standardized subplots, whose sizes follow a geometric series. To allow for different sampling intensities but at the same time to characterize the whole square kilometer, the number of hectare plots to be sampled depends on the requirements of the respective discipline. A hierarchical ranking of the hectare plots ensures that all disciplines monitor as many hectare plots jointly as possible. The BIOTA Observatory design assures repeated, multidisciplinary standardized inventories of biodiversity and its environmental drivers, including options for spatial up- and downscaling and different sampling intensities. BIOTA Observatories have been installed along climatic and landscape gradients in Morocco, West Africa, and southern Africa. In regions with varying land use, several BIOTA Observatories are situated close to each other to analyze management effects.

Aim In the transition between the southern Sudanian and northern Guinean zones of West Africa, numerous islands of predominantly semi-deciduous forests are interspersed in extensive savannas. During the past decades, human population and intensity of land use have increased. At the same time, almost nothing is known about the natural dynamics of this widespread forest-savanna mosaic and how they are altered by human activities. This was investigated with respect to past, present and future forest-savanna dynamics, which presumably influence northern Guinean biodiversity.Location The Comoé National Park (CNP) region in north-eastern Ivory Coast.Methods Landscape dynamics and the rates of anthropogenic deforestation and natural reforestation were retrospectively analysed by means of historical and recent aerial photographs and satellite images, directly relating the semi-natural conditions in the CNP to neighbouring, traditionally utilized countryside.Results From 1954 to 1996, the studied forest-savanna pattern proved to be remarkably stable, even with extensive land utilization outside the CNP. The contour towards the surrounding savanna and, thus, the size of 95.4% of 653 forest islands remained unchanged. Unvegetated surfaces also remained remarkably constant during the period from 1967 to 1996. Although dynamics were clearly higher outside the CNP as a result of human activities, the 913 unvegetated surfaces studied showed no general trend of decrease or increase, i.e. there was no response over the study period to an identified climatic shift. Anthropogenic deforestation and subsequent natural reforestation within the contours of the existing forest have occurred to a noteworthy extent only outside the CNP. For the period 1988-2002, the extent of deforestation was greater than the extent of reforestation (40% vs. 14%). By 2002, 62% of the original gallery forest along a 75-km section of the Comoé river had been cleared.Main conclusions With its remarkable overall stability, the landscape pattern inside the CNP has responded with resilience to varying influences (in particular climatic variations) and disturbances (e.g. episodic mass herbivory). A possible natural succession from savanna to forest appears to proceed only very slowly due to the counteracting effects of annual savanna fires and the lower climatic humidity of the area compared to the southern Guinean zone. Consequently, the forests should be considered as habitat islands rather than as habitat fragments. As deforestation outside the CNP has increased considerably, the pre-existing pattern of forest insularization is now becoming overlain in these non-CNP areas by a pattern of forest fragmentation. This will aggravate the ecological and genetic isolation of the undisturbed forests in the CNP, which are among the last remaining natural forests of the entire GuineoSudanian transition zone.

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