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‘Edge effects’ harming forests

A section of land that was previously forest is littered with debris in Preah Vihear after it was cleared and burned off earlier this year.
A section of land that was previously forest is littered with debris in Preah Vihear after it was cleared and burned off earlier this year. May Titthara

‘Edge effects’ harming forests

Even comparatively small patches of human intrusion into contiguous forestland disproportionately saps forests’ ability to trap harmful carbon, a recent study has shown, a finding that suggests Cambodia’s government may be underestimating the environmental damage caused by logging and development.

So-called “forest degradation” – unlike typical deforestation – occurs when forest cover is thinned or pockmarked by human development, but not entirely clear-felled.

However, even this selective cutting down of forest trees not only releases carbon but dries out the remaining plants, lowering their ability to capture carbon, according to the new study, published in science journal Nature Communications on December 18.

Human development increases the number of holes and edges a forest has, dramatically reducing its effectiveness as a carbon sink.

Marcus Hardtke, the Southeast Asia coordinator for German conservation group ARA, said that the problem of woodland degradation is large in Cambodia, where a patchwork quilt of logging and economic land concessions eat away at forests.

“Most of the forest death [comes from] degradation, not deforestation,” said Hardtke. “It’s death by 1,000 cuts.”

According to the new study, biomass volume within a kilometre of a forest’s edge can be 10-25 per cent lower than in the interior and, as a result, traps far less carbon. As roads, selective logging and even seemingly small or unobtrusive settlements push into previously unspoiled forests, the amount of forest edge multiplies.

These “edge effects”, the study’s authors found, account for up to 24 per cent of global carbon losses from forest damage, especially in the tropics.

“Considering that 70 per cent of the world’s forest area is within 1 km of the edge, the extent to which this response is found across the tropics is of critical importance to carbon trading schemes and climate change mitigation more broadly,” the study says.

The authors added that not accounting for edge effects can cause policymakers to overestimate the amount of carbon they can retain with available forest land, especially when setting targets for Reducing Emissions from Deforestation and Forest Degradation (REDD) programs.

Forest loss in Cambodia has accelerated faster than any other country in the world since 2001, peaking in 2010, according to a Global Forest Watch report in September, and development in Cambodia seems almost tailor-made to exacerbate edge effects.

“Problem is, the government gave out all these plantation permits,” said Hardtke. “These guys start logging, put a big farm in the middle, then log outside the boundaries. No one is watching or controlling this. Once local people see this, they start logging, too.”

The lack of accountability makes a mockery of attempts to implement REDD in Cambodia, he said.

Environment Ministry spokesman Sao Sopheap yesterday said that the Cambodian government currently looks only at total forest cover, rather than measuring biomass and degradation, and acknowledged that it may be missing important details, but said that the government plans to get more granular in the future.

The Forestry Administration wasn’t immediately available for comment yesterday.

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