# Informations et ressources scientifiques sur le développement des zones arides et semi-arides

Accueil du site Doctorat États-Unis 1997 Dynamics of biodiversity and human carrying capacity in the Senegal Sahel

## Gonzalez, Patrick Joseph

Titre : Dynamics of biodiversity and human carrying capacity in the Senegal Sahel

Auteur : Gonzalez, Patrick Joseph

Université de soutenance : University of California, Berkeley

Grade : Doctor of Philosophy (PhD) 1997

Résumé
Extensive field surveys over 7600 km$\sp2$ in Northwest Senegal and analyses of ecological and socio-economic data show that biodiversity and tree densities have declined in the last half of the 20$\rm\spth$ Century, that population densities have risen above carrying capacity, and that the natural regeneration of local species would most effectively augment the land’s ability to support people and lead towards sustainability. Species richness of areas of 400 ha declined from 64 $\pm$ 2 species ca.1945 to 43 $\pm$ 2 in 1993, an extremely significant $\rm(p<0.001)$ decrease. Densities of trees of $\rm h\ge3$ m decreased from 10.1 $\pm$ 0.3 trees ha$\sp-1$ in 1954 to $7.8\pm0.3$ trees ha$\sp-1$ in 1989, also extremely significant $\rm(p<0.001).$ Arid Sahel species have expanded from the North, tracking a concomitant retraction of mesic Sudan and Guinean species to the South. Vegetation zones have shifted at a rate of 500-600 m y$\sp-1.$ Correlations coefficients, t-tests, scANOVA, gradient analyses, principal components analyses, and canonical correlations analyses mark latitude and longitude, proxies for rainfall and temperature, as the most significant factors determining tree and shrub distribution. The rural population of 45 people km$\sp-2$ exceeded the 1993 carrying capacity of firewood from shrubs of 13 people km$\sp-2$ (range 1-21 people km$\sp-2).$ Charcoal use also exceeded trunk wood production. Standing wood biomass fell 2100 kg ha$\sp-1$ from 1956 to 1993, releasing CO$\sb2$ at a rate of 60 kg C person$\rm\sp-1y\sp-1.$ Seventy-seven percent of local people favor natural regeneration of local species over the plantation of exotic species. Natural regeneration is practiced traditionally, requires no special inputs, and encourages the propagation of multiple-use trees. This research has produced the first documentation of a large-scale decline in species richness and tree densities in the West African Sahel, the first range maps of all 126 tree and shrub species in the Senegal Sahel, the first complete and accurate list of the Wolof names of the 126 species, and the first large-scale carrying capacity analysis in the Sahel based on field data. The research provides a practical plan for sustainable natural resource management for international development organizations in the field. This could help improve the life of the Senegalese villager, for whom the work is ultimately destined

Mots clés : Ecology, Environmental science, sustainable development, Health and environmental sciences, firewood, Biological sciences Forestry

Page publiée le 6 mars 2015, mise à jour le 30 août 2017