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Deforestation: a lingering legacy

  • Researchers found that even if rainforest deforestation had stopped completely in 2010, the planet would still face about five or ten years’ worth of continued deforestation carbon emissions.
  • Their findings indicate that past deforestation will result in the extinction of 140 vertebrate species.
  • The authors say emissions and extinctions could be prevented through restoration.
  • However, other experts caution that increasing emphasis on restoration might detract from the importance of protection of still-intact forest.

When we humans cut down tropical forest, we have a good idea that there will be consequences. We know that clearing the land for a farm or a pasture or the timber it holds comes at the cost of a burst of carbon into the atmosphere, and that the habitat anchored by those trees will change pretty drastically, forcing animals, plants, and other organisms to adapt, move, or disappear.

What’s not as clear is how long those changes take to unfold. As a result, we may not have an accurate picture of the extent of carbon emissions and the loss of species from areas that we have already deforested.

“We haven’t been accounting for these emissions and these extinctions, and that’s quite a big [piece that is] missing,” said Isabel Rosa, an ecologist at the German Centre for Integrative Biodiversity Research in Leipzig, in an interview with mongabay.com.

Rosa is the lead author of a study in the journal Current Biology published this month that attempts to better understand the carbon and species extinction “debts” that we have to pay as a result of clearing forestlands between 1950 and 2009. To do that, Rosa and her colleagues created a computer model based on current data to “backcast” when and where these effects occurred or will occur.

“We have all the technology to really do a good job at monitoring landscape change [from now on],” Rosa said. “But we’re still going to have to always rely on models to go back in time and see what happened in the last 100 years and how that has impacted the future.”

Deforestation for cattle pasture in the Peruvian Amazon. Photo by Rhett A. Butler.

Key among the team’s findings is that, even if we had stopped cutting down rainforest in 2010, we would still expect the planet to face about the same amount of carbon emissions that we would get from five or ten years of continued deforestation. And, based on their modeling, that past deforestation would mean the end of another 140 vertebrate species – which is more than the total number of such species known to have gone extinct between 1900 and 2000.

While that’s a scary prospect, Rosa also sees these “time lags” as an opportunity.

“If we’re proactive and we invest in restoring these areas while the species is still trying to survive in the modified habitat, then we can still prevent further losses,” she said. Helping the forest grow back will also tamp down the carbon emissions, she said.

But she and her coauthors warn that the current focus in allaying deforestation seems to be primarily on protecting what’s standing.

“A lot of effort is being made on conservation and not as much on restoration,” Rosa said, adding that the conservation of existing habitats is “extremely important” nonetheless.

But, she said, “I think it’s really important that we look at all those degraded areas. We can do so much to prevent further carbon losses and species extinctions.”

The group’s research also highlights geographic shifts in deforestation. Their models tracked a well-known recent slowdown in the Amazon – though recent information seems to indicate that forest clearing there, primarily for pasture and agriculture, is once again on the rise. According to data from Global Forest Watch, Brazil’s deforestation rates peaked in 2004 and Peru’s rates topped out in 2012.

Percentage of tree cover loss in four countries over 14 years. The DRC surpassed Brazil for the top spot in 2013. Data accessed through Global Forest Watch.

However, Rosa warned that deforestation rates in the Congo Basin and Southeast Asia continue to climb, perhaps highlighting a worrying geographic shift in forest loss.

“We should try and prevent deforestation [from] ramping up in the Congo as a result of slowing down in the Amazon,” Rosa said. Currently, a lot of deforestation in the world’s second-largest rainforest, much of which exists in the Democratic Republic of Congo, is driven by small-scale farmers who clear land to grow food; but that appears to be changing. Industrial agriculture and logging companies have made significant developments, particularly in neighboring Republic of Congo. The country contains 26 million hectares of tree cover, an area about the size of Ecuador.

It’s also troubling that we know less about the Congo than we do about the humid forests in Southeast Asia and South America, Rosa said.

“We should really try and find ways that we can monitor deforestation in the Congo,” she added.

Other researchers who weren’t involved in this study say that Rosa and her colleagues’ research helps provide a clearer picture of the complexities of deforestation that has happened in the past.

“What they’ve produced is a very useful reminder that it will take time for any action we take to have an impact on emissions from deforestation, even if that action were effective enough to halt current and future deforestation,” said Valerie Kapos, a tropical ecologist and head of the climate change and biodiversity program at the United Nations Environmental Programme World Conservation Monitoring Centre.

Kapos said we’ve gotten pretty good at figuring out how much carbon will be emitted when a specific piece of standing forest is lost. But, “We tend to forget the fact that there is carbon sitting around that is still being emitted as a result of past deforestation,” she added.

Typically, some vegetation remains behind and decomposes as a persistent source of carbon, though the volume of downed wood, brush, and branches – and thus the amount of carbon that continues to trickle into the atmosphere – depends on how thorough the clearing was and for what purpose.

“This is one of the first studies – and probably the most rigorous study I’ve seen – that can estimate what the consequences are going to be decades in the future after you cut down rainforest now,” said Bradley Cardinale, a conservation ecologist at the University of Michigan in Ann Arbor.

Cattle grazing in a deforested area of Brazil. Photo by Rhett A. Butler.

However, Cardinale said he disagreed with the “implication” that protecting habitat won’t slow the tide of future extinctions.

“I worry that that sends a message to people that it’s too late, that even if we stop habitat destruction now, that we’re going to lose everything,” he added. “That’s just not true.

“The sooner we act, the better off we’re going to be and the more things we’re going to be able to save,” Cardinale said.

Kapos explained the trepidation: “The idea that restoration can counter [biodiversity loss] makes people very nervous.”

Even with efforts to reestablish habitats for the animals and plants that live in the forest, “It’s a very long time before restoration replaces like with like,” she said.

Unlike carbon, where we can offset the tonnage that’s liberated through deforestation by planting trees elsewhere, an area’s biodiversity isn’t so replaceable.

“We don’t know whether restoration can preempt that extinction debt by arriving at suitable habitat in an appropriate timeframe,” Kapos said.

Cardinale does agree with Rosa that the research showing that “we’re underestimating the consequences of our actions” points to an opportunity to compensate for deforestation.

“The good news is that this underestimate also means there’s time,” he said. “Those species are still here, and we have time to save them if we reverse our actions.”

But the window for action will pass quickly, he said.

“I think there’s an urgency. We don’t have a century to reverse them.”

Cardinale also said he would like to see this type of approach extended to other landscapes.

“Imagine we could get similar models, let’s say for grasslands,” he said. “You could basically model the extinction debt across the land surface of the planet.

“That would be a huge step forward.”

 

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