Earthshots: Satellite Images of Environmental Change

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Madagascar, the world’s fourth largest island, is located off the southeastern coast of Africa in the Indian Ocean. Because it is isolated from neighboring continents, almost all of its plant and animal species are found nowhere else on Earth.

In southwestern Madagascar, plants have adapted to a dry desert-like climate. These unique plants are so peculiar they cannot be classified into common classes like desert or forest. Many species there have small leaves and spines and can retain water very well—characteristics of succulents that are typical in deserts. They also have tall trunks, appearing more like trees. So the vegetation in this region often is named Madagascar Spiny Thicket.

This ecoregion, which extends across southern and southwestern Madagascar, has a long dry season. Most of the rain falls from October to April, but rainfall amounts can be erratic. The plants’ unusual adaptations allow them to survive the long dry periods. But this ecoregion is experiencing rapid deforestation, which is evident in this Landsat series.

Map of the featured area.

All of Madagascar is being threatened by deforestation, but this threat is most apparent in the Spiny Thicket region. Spiny Thicket has a naturally slow rate of growth and regeneration, making it especially vulnerable to the effects of deforestation. The primary threats are from small-scale but widespread clearing of trees for firewood, agriculture, and livestock grazing. Human population growth increases the demand on natural resources. This is part of the reason for the increased rate of deforestation here. For example, more land is needed for agricultural production.

Landsat images show more clearly the extent of changes to the Spiny Thicket ecoregion in southwestern Madagascar. Over the past four decades, rapid deforestation has occurred on both sides of the Linta River. Most of these images are from around the end of the rainy season (October to April) when vegetation is near its peak annual growth.

Looking at a more specific region within these images makes it clear that that the Spiny Thicket seems to be disappearing fast. Since 1990, this ecoregion has had the highest deforestation rate in the country.

Agriculture in this region is done by slash-and-burn. The fields are cleared by burning, then planted.

The forest is also used for charcoal production. Most households use charcoal to cook their daily meals. Even though this is less destructive than slash-and-burn, charcoal production causes the degradation of vast areas of the Spiny Thicket. Even when the Spiny Thicket regenerates, it does so as cactus scrub.

Landsat is uniquely suited to monitoring these types of land changes over large areas. Forests once covered Madagascar, but forest cover has been reduced to less than one-fourth of the island’s original extent. Information gathered by Landsat can help improve management of remaining resources.


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