Jean-Louis Devineau

“Ordinary biodiversity” in western Burkina Faso (West Africa): what vegetation do the state forests conserve?

The role of state forests in the conservation of the savannah environment of western Burkina Faso (West Africa) was assessed by considering the customary and fundamental biological components of plant diversity. The focus is on the “ordinary biodiversity” which constitutes the current environment of human populations and which generates their resources. Overall floristic composition, α, β, γ diversities and species accumulation curves of landscape units were compared inside and outside protected areas. Common species were identified according to their frequencies in landscape units and their local abundance. The occurrences of functional (life form, dispersion, etc.) and human-valued (current uses, potential threats, etc.) traits were compared. Current land uses outside protected areas have an unequal effect on the various components of plant diversity. Species richnesses and specific structures were all the more altered for woody species as agricultural pressure is high; conversely, they were maintained for herbaceous communities for which the proportion of wide-ranging species increased. The preservation of useful plant species on cultivated lands was obvious for woody species with edible fruits but less tangible for timber and service wood. It was deficient for species that furnish other non-wood products (e.g. leaves used as food or fodder), the conservation of which may be jeopardized where anthropic pressure is high. Given current land uses and dynamics, maintaining conservation areas in land use planning is crucial in order to preserve ordinary biodiversity.

Phenology of Woody Species Along the Climatic Gradient in West Tropical Africa

West tropical Africa (WTA) is known to be one of the most exposed regions in the world to climate change. The seasonality of rainfall and of atmospheric conditions, including a dry season lasting for several months in most of the area, strongly influences vegetation activity (Bourliere & Hadley, 1983; Breman & Kessler, 1995). Indeed, this region was already affected by severe and prolonged droughts in the 1970s-1980s. These events represent one of the major climate variations of the 20th century recorded at the global scale (Giorgi, 2002; Neelin et al., 2006; Redelsperger et al., 2006). The average annual rainfall deficit varied by ± 20% in higher rainfall zones and by 50% in lower rainfall zones. However, while these droughts were relatively uniform over most of WTA, the 1990–2007 period was characterised by a more complex pattern including large spatial variability (Lebel & Ali, 2009). Current projections of global change predict higher temperatures and lower rainfall, although opinions on temperatures are contradictory (Mearns et al., 2001; Haarsma et al., 2005; IPCC, 2007; Funk & Brown, 2009). More frequent extreme events are also expected in some parts of Africa (Hely et al., 2006; Frappart et al., 2009; Lebel & Ali, 2009).

Changes in the availability and uses of wild yams according to climatic dryness and land-cover in Western Burkina Faso (West Africa): a joint ecological and ethno-botanical approach using GIS and remote-sensing

The regional variability in the uses of wild yams is assessed according to their availability in relation with land-use and climatic conditions from the South to the North sudanian sectors in Western Burkina Faso. The study involves field studies and modelling of the geographical distribution of yams and seeks correlations between environmental and ethno-biological data. Terrain analysis consists of phyto-ecological surveys and interviews with local inhabitants. A cluster analysis of a multi-date image of data obtained by remote-sensing is used to assess land-cover. The Bayesian post-probabilities of occurrence of each species are inferred using Weight of Evidence modelling linked to a Geographical Information System. The model is implemented with land-cover units and annual Moisture Availability Index evidential-layers and is driven by species presence data. The probabilities of occurrence of each species throughout the whole area as well as within and without the protected areas and in the vicinity of the sites of enquiries are calculated. A multi-factorial analysis makes it possible to shed light on the relationships among land use, the availability of yams, the uses of yams, knowledge and local practice. Results provide statistical evidence of spatial association between the yam species and the environmental descriptors taken into account. The study also provides evidence of an important regional variability in the actual uses and knowledge of wild yams. The rather widespread use of wild yams as a food complement, in social relations and as merchandise in local trade in the North of the area studied, which is far less observed in the South, is one of the major components of this variability.

To what extent does land-use affect relationships between the distribution of woody species and climatic change? A case study along an aridity gradient in western Burkina Faso

The study aims at evaluating how land-use modifies the link between the observed distribution of species and the climatic variability and at detecting species involved in that modification. The area studied covers the phytogeographical transition between the South-Sudanian sector and the North-Sudanian sector in western Burkina Faso. It lies along an aridity gradient, of which the aridity index (UNESCO-MAB) ranges from 0.363 to 0.533. The data studied were derived from observations performed on 192 woody species in 603 vegetation survey plots inside and outside protected areas. The species turn-over (β diversity) and the mutual information were assessed along the aridity gradient inside protected areas on one hand and outside protected areas on the other. Our study shows that the statistical links between the geographical distributions of species and the aridity gradient differ according to whether the observations are performed inside or outside the protected areas. Anthropogenic disturbances, mainly agricultural in the region of study, result in a decrease in the β diversity and in the average mutual information between the distribution of all the woody species and the climatic gradient. Moreover, the variation in mutual information differs according to the species: it diversely decreases with agricultural land-use for most of them, but increases for some. Thus, land-use leads to species-specific changes in the realised climatic niches.

Caractéristiques structurelles et écologiques des phytocénoses de sous-bois des plantations privées de teck du département de l’Atlantique (Sud-Bénin, Afrique de l’Ouest)

Abstract Structural and ecological characteristics of private Teak plantations in the Atlantic Department, South Benin, were studied according to the synusial approach of phytosociology in order to contribute to the sustainable management of the plantations. The study of dendrometric characteristics of Teak plantations was done by establishing two temporal plots, each of 1 are. In each plot, the stem girth of the trees and the total height of three mean trees were measured. A total of 99 vegetal synusias has been described, then combined into 18 phytocoenoses. Ecological characteristics are also studied.

Groupements floristiques et capacité de régénération des espèces ligneuses des sanctuaires boisés dans l’aire culturelle bwaba (département de Bondoukuy, Ouest Burkinabé)

Résumé Afin d’évaluer l’intérêt des sanctuaires boisés pour la conservation de la flore ligneuse au sein de l’aire culturelle bwaba dans l’Ouest burkinabé, leur recensement exhaustif a été réalisé dans le département de Bondoukuy. Les investigations portent sur la répartition spatiale des sanctuaires, leur distribution de taille, leur flore, la densité de régénération de leurs espèces végétales. Elles portent aussi sur la variabilité des richesses spécifiques ? ? en fonction de la taille des sanctuaires et en fonction des groupements phytosociologiques mis en évidence. Ces travaux montrent que les sanctuaires boisés du département de Bondoukuy s’apparentent aux forêts sèches soudaniennes à Anogeissus leiocarpa et Diospyros mespiliformis; ils apparaissent comme des lieux de conservation d’espèces sensibles aux feux. Ils sont situés à proximité des lieux d’habitation et sont par ailleurs sujets à l’invasion par le neem, Azadirachta indica, qui appauvrit la flore forestière indigène. La flore des sanctuaires boisés apparaît ainsi menacée par l’anthropisation et la fragmentation des milieux ainsi que par leur sensibilité aux espèces invasives.

Phytocénose à Mallotus oppositifolius et Macrosphyra longistyla dans le sous—bois des plantations privées de teck (Tectona grandis) de la commune d'Abomey-Calavi, Sud-Bénin

Abstract A study has been undertaken in the natural undergrowth of private teak plantations in Abomey—Calavi using the synusial approach to phytosociology. Pedological and topographical factors and private teak plantation production within plant communities have been studied. Mallotus oppositifolius and Macrosphyra longistyla community is identified on acid clayey—sandy soils. It is composed of eight vegetal synusia and represents the fourth stage growth of the vegetation succession in the study area. Mean diameter of teak in this plant community varied between 5.7 cm and 15.8 cm while the mean height is between 6.5 m and 13 m and, the basal area between 10.7 m2/ha and 18.9 m2/ha. This community is indicative of the most productive forest sites of the municipality.