Big carbon gains from restoring forests

We’re learning more and more about what’s happening in the world’s tropical forests, and the news usually isn’t good.

Just this week Cosmos reported on a study showing that tropical soils are more sensitive to global warming than previously thought, and we recently learnt that tropical plants close to the equator are the most at risk from climate change and that tropical animal species are six times more sensitive to forests being broken up than are temperate species.

All is not lost, however. An international study just published in the journal Science shows that actively restoring degraded forests in Southeast Asia improves carbon storage recovery by more than 50% when compared with just letting them regenerate naturally.

That’s significant for two reasons. The first is that more than half of the world’s aboveground carbon is stored in tropical forests. The second is that degraded forests are often dismissed as having no ecological value.

Rainforest seedlings
Seedlings for restoration work growing in nurseries. Credit: Sonny Royal, SEARRP

This misconception has marked degraded forests as prime candidates for full conversion to agricultural plantations, the researchers say, despite evidence of their ability to continue to contribute to the ecosystem.

“Not long ago, we treated degraded tropical forests as lost causes,” says co-author Greg Asner, from Arizona State University, US. “Our new findings, combined with those of other researchers around the world, strongly suggest that restoring tropical forests is a viable and highly scalable solution to regaining lost carbon stocks on land.”

Scientists from 13 institutions, led by Christopher Philipson and Mark Cutler from Scotland’s University of Dundee, studied an area of tropical forest in Sabah, in Malaysian Borneo, that was heavily logged in the 1980s and subsequently protected from further logging or conversion to plantation agriculture.

To assess forest recovery, they mapped the area using their Global Airborne Observatory, equipped with powerful lasers and spectrometers, in 2016. The resulting maps revealed the location and amount of carbon stored above ground across thousands of hectares of forest.

Areas left to regenerate naturally recovered by as much as 2.9 tonnes of aboveground carbon per hectare of forest each year, highlighting the ability of degraded forests to recover if protected from full agricultural conversion.

That rose to 4.4 tonnes for areas that underwent active restoration through methods such as planting native species, removing tree-climbing vines, and thinning vegetation around saplings to improve their chances of survival.

Full recovery in a naturally regenerating logged forest would take around 60 years, the study suggests, while recovery for an actively restored forest takes just 40 years.

However, the current carbon price is still not sufficient to pay for the cost of restoration, the researchers say, limiting the possible impact of a new approach.  They suggest that new carbon offset programs could potentially fund these restoration costs.

The project included collaboration with South East Asia Rainforest Research Partnership (SEARRP) and the Yayasan Sabah Group.

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