Understanding environmental issues using system dynamics methods. pressure on natural resources in southern madagascar

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  • Publié le : 8 avril 2011
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La forêt sèche tropicale de l’Androy, extrême sud de Madagascar, est menacée de l’extinction par plusieurs sources de perturbation. Nous pourrions voir dans quelques littératures et des documents gouvernementaux l’affirmation que la population rurale ne se soucie pas de conservation de ressources naturelles. Au regard de ce sujet, la gestion durable du secteur forestier rentre dans unsystème complexe et multidisciplinaire. Cet article explique la déforestation comme un point central de plusieurs facteurs qui causent les problèmes environnementaux dans l’Androy. Ce faisant, la dynamique des systèmes est la méthode utilisée pour analyser les relations causales entre des variables socio-économiques et environnementales. Plusieurs facteurs s’entremêlent dans le problème de ladéforestation dont le plus évident serait des facteurs socio-économiques, démographiques et climatiques. Dans ce sens, une simulation sera effectuée en considérant le pôle social, économique et environnemental.
Mots clés : Androy, forêt sèche, ressources naturelles, méthode de la dynamique des systèmes, multidisciplinaire.
The tropical dry forest in Androy, southern Madagascar, is threatenedwith disappearance by many activities. We can see in the literature and government documents the fact that the rural population is little concerned by natural resources conservation. To debate this complicated subject, multidisciplinary approach allows us to understand the different dynamics. This paper explains deforestation as a central concern among several factors causing the environmentaldegradation in Androy. To do this, we use a system dynamics methodology for analyzing interlinks and causal relations between socio-economic and environmental variables. Deforestation is driven by many interacting factors such as a limited suite of recurrent core variables, of which the most evident would be socio-economic conditions, populations’ growth and climate factors. Taking this into account,simulations of a socio-economic-environmental model is conducted.

Key words: Androy, Dry forest, Natural resources, System dynamics method, Multidisciplinary.
Throughout history, demand for timber, forest products and agricultural land have had a negative effect on the world’s forest resources. Such forest loss is the result of many pressures, acting in various combinations indifferent geographical locations (Geist and Lambin, 2002).
In this paper, we are interested in tropical dry forest and open woodlands. According to (FRA, 2005), only about seven percent of the Earth’s dry land, are covered by tropical dry forest, with all of the forests of the southern part of Madagascar belonging to this zone. Dry forest in Madagascar is fragile because of its high levels ofspecies endemism with the flora and fauna having come to form part of a unique ecosystem thanks to the island’s isolation. There are a wide range of endemic species and 48% of the genera of plants are unique in the island (Koechlin, 1972). The “spiny forest ecoregion” is also listed as one of the 200 most important ecoregions (Olson et al, 2002). In 1970, ten years after gaining independence fromFrench colonization, the Malagasy forests, particularly in Androy were becoming increasingly depleted due to hatsake (slash and burn), ororaketa (cactus burning for cattle herding), timber harvest and charcoal production (Sussman et al., 1994; Sussman et al, 2003; Fanokoa, 2007).

The study zone is situated south of the tropic of Capricorn between 24° and 26° South and 44° and 47° East. The areais bordered by the Mandrare and Menarandra rivers (figure-1). Climate is semi-arid, with average annual precipitation varying from 35 centimetres on the south-western coast to 70 centimetres toward the north. Irregular rainfall makes the region subject to cyclic drought. Androy’s forest is characterized by xerophilous bush, dominated by species of endemic plant families: the Didiereaceae and the...