Research suggests that forests in Madagascar were not destroyed by climate change or any natural disaster. Humans set fire to the forests to make way for feeding their cattle.
Human activities have caused profound effects on Earth’s atmosphere in the past few centuries after the introduction of power-driven machinery and growth of factories.
But a new research suggests that humans were changing planet’s environment long before the industrial revolution. A team of researchers from MIT and the University of Massachusetts shows a direct link between the widespread loss of Madagascar forests and the activities of human settlers.
Researchers suggest that around 1,000 years ago forests in Madagascar were not destroyed by climate change or any natural disaster; it was the humans who set fire to the forests to make way for feeding their cattle.
Researchers reached to the conclusion after looking at the composition of two stalagmites from a cave in northwestern Madagascar. Stalagmite is a mineral deposit that can be preserved for thousands of year. It can work as a time capsule and provides a unique opportunity to peek into the past and to observe environmental changes.
From their analysis, researchers found that both stalagmites’ calcium carbonate composition suddenly and completely changed from carbon ratio isotopes associated with trees to those consistent with grasslands within just one century. The oxygen isotope levels remained unchanged in both stalagmites indicating there was no dramatic climate change. The permanent landscape transformation was possibly caused by humans.
“We went in expecting to tell just a climate change story and were surprised to see a huge carbon isotope change in both stalagmites. Both the speed at which this shift occurred and the fact there’s no real climate signal suggest human involvement.” David McGee, Assistant Professor in the Department of Earth, Atmospheric and Planetary Sciences at MIT said.
It is also noticeable that populations of many large animals in the region also declined dramatically around the same period. The megafaunal extinction is likely triggered by habitat loss and widespread destruction of forests at that time.
Trees and shrubs have a fixed isotopic ratio of carbon-12 while grass has carbon-13 isotopic ratio. Researchers observed a sudden shift in the ratio of carbon-12 to carbon-13 around 1,000 years ago in both stalagmites.
“What we see in the record is that the change from carbon isotopes that look like forest, to isotopes that look like grassland, happens really rapidly, within a century and it would be unusual for a forest to naturally completely turn into grassland that quickly.” McGee said.
Researchers also found evidence that human settled on Madagascar around 3,000 years ago and introduced cattle to the land around 1,000 years ago. Humans possibly used “slash and burn techniques” to create pasture for the cattle where they can graze.
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“The transformation of ephemeral forager to dedicated agro-pastoralist occurred, probably across Madagascar around 1,000 years ago,” said co-author Laurie Godfrey, professor of anthropology. “We know that a dramatic transformation occurred in the northwest. We know that this transformation was not triggered by climate change. But we don’t yet know whether similar shifts also unrelated to natural aridification, occurred elsewhere on the island, and if so, when, exactly. We are currently seeking to answer these questions.”