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Madagascar : the forest in danger

May 22, 2000

Madagascar's forest is one of the most threatened in the tropical world. In the south-west of the island cultivation of maize on areas cleared by slash-and-burn methods is the main cause of deforestation which, particularly intense in this area, is increasing year by year. Research scientists from IRD (Institut de recherche pour le développement) and from CNRE (the Madagascan National Centre for Environmental Research) have been working on the possibility of forest regeneration once land cultivated in that way is abandoned. It appears that, unlike in other areas of the wet tropical zone, deforestation in this part of Madagascar is irreversible. And the result is a sharp decline in plant biodiversity.

More than 20% of the territory of Madagascar is covered by forest, which extends to about 13 million hectares. Deforestation is now occurring at alarming rates. Each year 200 to 300 ha of forest disappears. This process has intensified recently, especially in the south and south-west of the island. In the Mikea forest for example, the surface area cleared has quadrupled since the end of the 1980s. In order to investigate this, as, part of the programme GEREM (Rural and Environmental Management in Madagascar) researchers from IRD and CNRE have studied the changes taking place in the forest ecosystem in relation to trends in agricultural activity in this region of Madagascar.
In the south and south-west of the island, deforestation can be attributed largely to the increase in maize growing on land cleared by slash-and-burn methods known locally as hatsake. This pioneer form of agriculture is developing rapidly at the expense of forest. Several factors are influencing this: an increase in population pressure owing to the arrival of migrants, saturation of the most fertile land given over to intensive cultivation and Government's relaxation of controls over forest clearance. Furthermore - and this is the strongest factor - maize, originally a subsistence food crop, has become a mainly commercial commodity in response to the needs of the national market and that of Reunion Island. Maize therefore never ceases to gain ground over the forest.
The hatsake system is not a sustainable approach to farming. The farmer summarily cuts a space in the forest, burns the residue and, as soon as the first rains arrive, sows the maize. For the first three years, if climatic conditions are favourable, yields are satisfactory (they can exceed 1500 kg of grain per hectare), without much work input, which is an advantage given the extent of the areas cultivated. However, crops subsequently decline to reach very low levels (less than 500 kg/ha) after five or six years. This deterioration results from soil impoverishment and invasion of plots by weeds. These could be removed by considerable weeding effort but this is rarely done owing to the large expanses of land given over to maize. The farmers most often just burn the remaining weed straw at the end of the dry season in order to prevent them from spreading. Having produced crops on the same plot for 5 to 10 years, the farmers find themselves forced to abandon it in favour of a plot newly cleared from the forest.
The researchers looked into whether or not the forest could regenerate once plots cultivated after slash-and-burn clearance had been abandoned. Using a set of indicators relating to the vegetation and soils, they monitored what happened in certain sites which had been abandoned for varying lengths of time (from 2 to 30 years). The results indicate that the deforestation is irreversible. Once cultivated plots give way to wooded savannah and the forest ecosystem is not restored, even 30 years after abandonment. Grasses, become a structural part of the ecosystem, also prevent any renewed cultivation of these areas by hatsake. In the framework of the GEREM research programme, the scientists are studying the possibility of other types of farming system that would prolong the productive life of the land in question and give acceptable yields.
Why is it that in South-West Madagascar, unlike in most humid tropical regions, the forest is observed not to regenerate? First, the land no longer cultivated is used for other purposes (grazing, timber and firewood gathering) and regularly swept by bush fires. Also, the climate is more arid in the south of Madagascar making the dynamics of vegetation development slower. Moreover, the endemic forest flora is fragile and poorly competitive which is a hindrance to any reconstitution of secondary forest.
Madagascar is experiencing one of the most preoccupying processes of deforestation in the tropical world. Although the ecological cost has not been completely assessed, certain major points are indeed emerging. The degree of erosion of the biodiversity is very high. According to one estimate from a survey in the Mikea forest, the deforestation is causing the loss of 75% of the original plant species. Among these are species that are valuable economically, exploited for timber or used as medicinal plants. This is all the more alarming when it is realized that the Madagascan forests harbour almost all the island's endemic species.

Institut de Recherche pour le Développement, Paris (IRD)