A new study has once again emphasized the importance of restoring degraded tropical forests in the fight against climate change.

Using high-resolution satellite imagery, the study identifies more than a million square kilometers (386,000 square miles) of lost tropical rainforest across the Americas, Africa and Southeast Asia as having high potential for restoration.

The researchers say there’s no time to waste on reforestation efforts, but caution that the type of reforestation undertaken must be carefully considered.

Countries such as China have increased their forest cover through the extensive planting of a single tree species, but studies have shown that monoculture tree plantations are inferior to natural forests when it comes to capturing carbon, hosting wildlife, and providing other ecosystem services.

JAKARTA — The loss of tropical rainforests the world over is a major contributor to the global climate crisis. But that loss isn’t irreversible, according to a new study that has identified deforested areas spanning more than twice the size of California that can be brought back to life.

The paper, published July 3 in the journal Science Advances, estimates there are more than a million square kilometers (386,000 square miles) of lost tropical rainforest across the Americas, Africa and Southeast Asia with high potential for restoration.

“Restoring tropical forests is fundamental to the planet’s health, now and for generations to come,” said lead author Pedro Brancalion, from the University of São Paulo. “For the first time, our study helps governments, investors and others seeking to restore global tropical moist forests to determine precise locations where restoring forests is most viable, enduring and beneficial. Restoring forests is a must do — and it’s doable.”

Reforesting these “restoration hotspots” would have the least cost and risk and at the same time bring the most benefits, such as carbon storage and biodiversity conservation, according to the researchers.

“We were surprised at the large area of hotspots found across global rainforests, a total of 101 million hectares,” study co-author Robin Chazdon, from the University of Connecticut, told Mongabay. “This area is larger than the combined area of Sweden and Spain. And these areas are found in all continents and across dozens of countries.”

The researchers used high-resolution satellite imagery and the latest peer-reviewed studies on four forest benefits — biodiversity, climate change mitigation, climate change adaptation, and water security — and three aspects of restoration effort — cost, investment risk, and the likelihood of restored forests surviving into the future — to assess and “score” all tropical lands worldwide in 1-square-kilometer (0.4-square-mile) blocks that retained less than 90 percent of their forest cover.

The researchers found that the top six countries with the highest mean score were all in Africa: Rwanda, Uganda, Burundi, Togo, South Sudan and Madagascar. That gives these countries the highest potential for feasibly achieving multiple restoration benefits.

Chazdon said they scored highly because while most of them had lost tropical moist forests, they had high potential to recover biodiversity, carbon, and water resources through forest restoration efforts.

“We were surprised to find such a concentration of highly ranked countries in a single continent,” she said. “The study really highlights the high potential for successful rainforest restoration outcomes in these African countries.”

The five countries with the largest restoration hotspot by area are Brazil, Indonesia, India, Madagascar and Colombia.

Another encouraging finding is that the majority of the restoration hotspots — 73 percent — were identified in countries that had committed to restore their rainforests by participating in the Bonn Challenge, a global initiative launched in 2011 that calls for 1.5 million square kilometers (579,000 square miles) of the world’s deforested and degraded land to be restored by 2020, and 3.5 million square kilometers (1.35 million square miles) by 2030.

To date, 59 national governments, private associations and companies have made Bonn Challenge commitments to restore 1.7 million square kilometers (658,000 square miles) of forest.

“It’s encouraging that so many hotspots are located in countries where restoring forests and landscapes is already a priority,” Brancalion said.

No time to waste

Chazdon said these hotspot countries should act quickly to restore their rainforests, given that more than half of the world’s tropical forests have already been lost or seriously damaged, and much of the remaining forest cover is under threat.

“We need forests to protect watersheds, to mitigate climate change, and to conserve biodiversity,” she said. “As a result of forest loss and damage we are losing species that need forests, diminishing our water supplies, losing soil and productive land, reducing rainfall, and emitting carbon dioxide to the atmosphere.”

Despite various commitments to halt deforestation made by governments and businesses, forest loss remains a widespread problem in tropical countries. The tropics lost around 120,000 square kilometers (46,300 square miles) of tree cover last year, an area the size of Belgium, according to data from the University of Maryland.

While this number is down from the previous two years, it’s still well above the 18-year average since data collection began in 2001. The tropics lost around 170,000 square kilometers (65,600 square miles) of forest cover in 2016, and 160,000 square kilometers (61,800 square miles) in 2017.

Last year, deforestation in Earth’s biggest rainforest, the Brazilian Amazon, reached the highest level in a decade, spanning an area 134 times the size of Manhattan’s land mass.

Things are only expected to get worse under the country’s new president, President Jair Bolsonaro. Since taking office at the start of 2019, the Bolsonaro administration has dismantled environmental protections and institutions by firing or not replacing top environment officials, loosening controls on economic exploitation of the Amazon, and halting the demarcation of indigenous lands.

Environmentalists have expressed concern that Bolsonaro’s policies will clear the path for unchecked deforestation, with the rising deforestation rate primed to mark 2019 as one of the worst years for forest loss in recent memory.

Monoculture plantations vs. natural forests

“If we don’t act now it will be too late, as climate change is already affecting forest functions and the opportunities for restoring and protecting forests will decrease dramatically,” Chazdon said.

However, she added that restoration “involves far more than simply planting trees.”

“One challenge is to define what reforestation can and should achieve, as it is not always focused on restoring ecosystems, enhancing rural livelihoods, or providing a broad range of ecosystem services,” she said.

A broader approach of landscape-scale restoration has multiple benefits, such as reducing species extinctions, mitigating climate change effects, and promoting sustainable livelihoods.

On the other hand, reforestation efforts that rely on establishing monoculture tree plantations — one species of tree planted across a wide area — have been shown to provide only limited benefits, and don’t last long enough to make a significant impact.

China, for instance, managed to increase its tree cover by 32 percent by 2015 through its ambitious reforestation policies aimed to mitigate floods. But most of these reforestation efforts relied on simply planting one tree species. Critics say this approach doesn’t qualify as restoration, since monoculture plantations are often poor replacements for natural habitat and provide fewer ecological benefits.

According to a 2010 study, agroforestry and tree plantations support 35 percent fewer species than primary forests, with many wildlife species only found in mature tropical forests.

And even though monoculture tree plantations can be grown quickly, they tend not to survive for long. The longevity of timber plantations, for instance, is heavily dependent on shifting market demand for wood. These plantations can be abandoned if they’re seen as a bad investment and replaced with crops with higher economic value once they’re harvested.

“Carbon is being stored in these systems, but many of these trees will not live for very long,” Chazdon said.

And even if they do survive for a long time, their climate benefits are still paltry compared to natural forests, which studies have found to be 40 times more effective than plantations for storing carbon.

Charlotte Wheeler, a forest researcher at the University of Edinburgh, said monoculture tree plantations couldn’t replace natural forests in mitigating climate change. She called natural forests “the only option that can realistically help mitigate climate change.”

One of the major reasons plantations aren’t ideal for carbon storage is that regular harvest and clearing tends to release carbon dioxide every 10 to 20 years. However, natural forests, when left undisturbed, will continue to store the carbon in perpetuity.

That said, monoculture tree plantations still have a role to play in reforestation efforts, according to Chazdon. In some places, establishing monoculture tree plantations may be the best option, such as in areas with poor conditions for natural regeneration, she said.

“One of the feasibility layers in our study is a measure of the variability associated with biodiversity recovery through natural regeneration,” Chazdon said. “In areas with high variability (high uncertainty), plantations are a better investment and in areas where uncertainty is low, natural regeneration is a lower-cost approach.”

Monoculture plantations, like timber plantations, can also contribute to forest conservation by sparing remaining natural forests from being logged or cleared for farming.

“To maximize long-term success in reforestation, a variety of approaches are needed and it is important to consider the impact on rural people and involve them in the process,” Chazdon said. “There is a place for monoculture plantations, but they should not replace native ecosystems or be grown in areas that have a high potential for natural regeneration.”

Brancalion said the new study could help inform policymakers and advanced forest restoration agendas, from setting targets on the size of restored areas to prioritizing where and how to restore.

“With the tools we have developed, countries, companies and other actors who have pledged to restore forests have the precise information they need to roll up their sleeves and dive into the difficult work of bringing our forests back,” he said.

“There are no shortcuts when it comes to forest restoration, but there is low-hanging fruit that we need to seize now, before it’s too late.”

Banner image: Drained, cleared, and burned peat forest in Indonesian Borneo. Image by Rhett A. Butler/Mongabay.

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