Madagascar concentrates on an island territory a mosaic of natural environments that few countries can claim. Humid forests of the east, spiny thickets of the south, mangroves of the west, savannas of the highlands: each environment obeys distinct climatic, geological, and biological constraints. Understanding what differentiates these environments also measures why their degradation does not follow the same trajectories and why restoration responses vary so much from one region to another.
Humid forests of the east versus spiny thickets of the south: two climatic extremes
The precipitation gradient between the eastern coast and the southwestern part of Madagascar produces radically opposing environments. The dense humid forest, fed by the trade winds, receives rainfall volumes several times higher than those of the spiny bush, where drought can last most of the year.
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| Criterion | Humid forest of the east | Spiny thicket of the south |
|---|---|---|
| Rainfall | High, spread over most of the year | Very low, concentrated over a few weeks |
| Canopy | Dense, stratified over several levels | Low, open, dominated by Didiereaceae |
| Endemism | Very high (lemurs, reptiles, orchids) | High, with plant families unique to Madagascar |
| Main pressure | Slash-and-burn agriculture (tavy) | Charcoal production and overgrazing |
| Natural regeneration capacity | Rapid if the soil remains in place | Very slow, skeletal soils |
This table highlights a fundamental imbalance: the humid forest regenerates faster but faces constant pressure, while the spiny thicket, once destroyed, hardly returns on a human timescale. Restoration tools must therefore be designed for incomparable time scales.
To better situate the different types of environment in Madagascar within their biogeographical context, it is also necessary to integrate intermediate environments, often overlooked in classical approaches.
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Highland savannas and dry forests of the west: environments shaped by fire
The central highlands and western plains share a common point that institutional documents rarely mention first: fire is the main structuring factor of these landscapes. Annual bushfires, whether pastoral or accidental in origin, maintain the grassy savanna and prevent forest recolonization.
In contrast, the dry deciduous forest of the west, when protected from fire, develops a closed structure with species of baobabs and rosewoods absent from the neighboring savanna. The difference between these two environments is less about rainfall than about the frequency of fires.
Assisted natural regeneration on degraded lands in the center
Since the early 2020s, assisted natural regeneration (ANR) has emerged as a restoration lever in degraded agro-forestry landscapes. Partnerships between the FAO, the GEF, and other donors support Madagascar in a strategy that no longer limits restoration to protected areas but integrates it into productive territories: agricultural zones, pastures, fragmented shrub savannas.
- ANR relies on the protection and management of spontaneous regrowth, which reduces costs compared to traditional plantations.
- National restoration goals now mention millions of hectares of degraded land to be restored by 2030, a notable scale change.
- On the ground, dynamic agroforestry projects combine trees and crops to restore soil fertility while maintaining food production.
This paradigm shift shows that the restoration of degraded savannas involves agricultural integration, not isolation.
Mangroves and coral reefs: the land-sea interface under pressure
The mangroves of the west coast form one of the island’s most productive ecosystems. They protect the coastline, serve as nurseries for fish, and store carbon in their sediments at rates significantly higher than those of terrestrial forests.
The coral reefs of the northwest and southwest complement this coastal system. Their health directly depends on the quality of the waters coming from the watershed: sediments from upstream deforestation, agricultural pollution, urban discharges.
A degradation that moves up the watersheds
The Malagasy specificity lies in the direct connection between the degradation of the highlands and that of marine environments. The erosion of lateritic soils, visible from space as red rivers, transports considerable volumes of sediment to the estuaries. The destruction of a mountain forest translates, a few years later, into the suffocation of a coral reef located sometimes several hundred kilometers downstream.
This interdependence between terrestrial and marine environments explains why sectoral approaches (forests on one side, fishing on the other) fail to stabilize coastal ecosystems.
Endemism and fragmentation: what Malagasy biogeography implies for conservation
Madagascar is classified among the global biodiversity hotspots. Its insularity and tropical position have produced one of the highest rates of endemism in the world, both for flora and fauna.
The fragmentation of habitats adds a layer of complexity. Each isolated forest fragment functions like an island within the island, with animal and plant populations gradually losing their genetic diversity. Biological corridors between forest blocks then become a priority conservation issue, as they allow gene flow between populations.
The ecosystem profile created by Conservation International in 2014 already highlighted this fragmentation dynamic. Since then, forest cover loss has continued, making these corridors even narrower and more vulnerable to fires and agricultural expansion.
Each type of Malagasy environment carries an irreplaceable part of this biological heritage. The disappearance of a spiny thicket in the south cannot be compensated by the protection of a humid forest in the east: the species involved are different, as are the ecological functions. This non-substitutability between environments makes conservation in Madagascar more demanding than elsewhere, and requires tailored responses for each bioclimatic region.