Abstract
This study is a contribution on information needs for the
potential carbon sequestration of savanna ecosystems. The research is
implemented in six Protected Forests of Senegal (Welor, Patako, Ouli, Bala-Est,
Kantoora and Mampaye), selected in various SoudanoGuinean and Guinean
ecosystems. The method is manifold including forest inventory, biomass
collection for allometric models development, dendrometry analysis, survey
plots monitored since 1993 and vegetation cover mapping.
From the data collected and analysed, 3 allometric models are
suggested based on quadratic, cubic and polynomial 3rd order
regressions. Carbon stock (above ground woody biomass) assessment based on
these models give a coefficient of determination r2 >0.9 and the
ANOVA tests shows a very low difference between mean values of experimental
data and model outputs. The application of these model on inventory data shows
low carbon stock for Welor (3-7 tC/ha), but for Mampaye (20-50 tC/ha) and
Kantora (40-47 tC/ha) the carbon stocks was better. Intermediate cases are Ouli
(12-20 tC/ha), Bala (18-28 tC/ha), and Patako (13-33 tC/ha). Most of the
biomass is trapped on individuals with DBH> 20 cm. Nevertheless, the carbon
dynamics is carried by young plants with a real growth potential.
Permanent plot data (3 plots of 1ha) show that carbon stocks
are essentially held by few species; mainly those with rapid growth. Species
with high contribution to total biomass are Pterocarpus erinaceus, Bombax
costatum and Terminalia macroptera. Hence, the specie
contribution to carbon stocks is strongly linked with its frequency, its
possibility to grow fast and its resilience to adverse stresses. The species
with rapid growth are Detarium senegalense and Bombax
costatum, followed by Anogeissus leiocarpus, Lannea microcarpa,
Pterocarpus erinaceus, and Terminalia macroptera.
The analysis of tree rings using dendrometry methods revealed
the good potential for tree dating and the possibility to link the tree ring
growth with parameters such as rainfall. The use of this method is very fuzzy
for tropical samples, but some samples gave good results that confirm the slow
growth rate of savanna species. With multiple strains in savanna ecosystems
such as fire, drought and competition, young plants do not necessarily have a
faster growth rate than mature trees as suggested by classical ecological
theories.
The low net productivity of savanna ecosystems results in
relatively low carbon sequestration compared to tropical forest stands, and
this required a measure of cautious for potential benefits from CDM projects.
The model outputs of carbon dynamics show several biomass removal factors such
as fires, wood extraction, slash and burn agriculture, overgrazing, with direct
effects on carbon stocks. This overall environmental degradation are associated
with climatic, political and economical factors that leads to high population
vulnerability that require various adaptation strategies, more vital for
population resilience to CC than the new misty carbon economy.
Par délibération, la Faculté
des Sciences et Techniques et l'Institut des Sciences de l'Environnement ont
décidé que les opinions émises dans les dissertations qui
leur sont présentées doivent être considérées
comme propres à leurs auteurs et qu'ils n'entendent leur donner aucune
approbation ni improbation.
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