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Climate Change Measured by Tree Growth

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Scientists are studying the effects of climate change by measuring tree growth

It is just after sunrise but the forest canopies in North Karnataka’s Sirsi are already a cacophony of activity. Woodpeckers drum on tree trunks. Sunbirds, small enough to fit into the palm of your hand, flit through vines with their distinct high-pitched trills.

But 25 metres below, on terra firma, and too busy to pay attention to the medley in the canopy, field researcher H.V. Raghavendra quietly goes about his work. To anyone watching, much of Raghavendra’s work would appear boring — maybe even bizarre.

Armed with a measuring tape, he jots down the girth of giant trees and the height of barely-noticeable seedlings unfurling their first leaves on the wet forest floor. He digs out coin-like ‘i-buttons’ buried in the wet soil to make sure they are doing their jobs: recording soil temperature. Small nets suspended from tree trunks catch falling leaves. Raghavendra will collect the leaf litter every month and then dry, powder and weigh each batch at his field station a few kilometres away before sending them to Bengaluru.

These peculiar exercises are aimed at deciphering answers to some of the most pertinent questions confronting the world today: how do changing weather patterns affect forests? What are the larger implications for India’s forests?

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Currently, the team monitors 11,726 trees (of nearly 400 species). And the data has begun revealing interesting nuances in tree growth, says Sankaran. “We are learning that in dry forests, tree girths can shrink substantially in the dry season, sometimes more than they grow in the wet season,” he says.

And preliminary results from the Andaman rainforests suggest that during years of normal rainfall, the forests act as carbon sinks, drawing carbon dioxide from the atmosphere. “However, during drought years, they switch to being sources, releasing more carbon dioxide than they absorb,” adds Sankaran. “This can have important implications for carbon cycling in the future, especially if droughts become more frequent, as has been predicted.”

These are exactly the kind of results the team hopes to generate in the coming years. The team’s data on local plant physiology and weather can also be used to refine existing climate prediction models that are now based on estimates from other parts of the world.

“But watching trees grow is slow business,” says Ratnam. The natural processes span decades; the first detailed results will start pouring in four years from now. Each plot involves intensive work and challenges include securing long-term permits to conduct their research in forested areas.

But then, studying vegetation is not considered as ‘interesting’ as studying animals. “Also, people often don’t see a direct societal impact, so it is difficult to convince them about the value of this data,” says Ratnam. “But with the interesting results we have been getting, we hope this will change this soon.”


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