Sprawling across the heart of Africa, the Congo basin covers 3.7m square kilometres and is home to the planet’s second-largest tropical rainforest after the Amazon. The forest spans six countries in central and western Africa: Cameroon, Central African Republic, Democratic Republic of Congo (DRC), Gabon, Equatorial Guinea and Republic of Congo. It contains thousands of plant, bird and mammal species. As the reservoir for a quarter of the world’s carbon, it is sometimes referred to as the Earth’s “second lung”.

Yet the forest is diminishing rapidly, with serious implications for regional ecosystems and economies, as well as climate change.

The disputed questions of where and why deforestation is occurring, and what might help to slow it down, must be answered if governments and non-state actors are to reverse the trend.

Although there is no argument that deforestation is proceeding, academics disagree sharply on its rate. The latest turn in the dispute focuses on a study published in July 2013 by the European Commission’s Joint Research Centre (JRC), which said that deforestation across the Congo basin had fallen by about one-third since 2000. Using satellite imagery, the report claimed that between 2000 and 2010, an average of 2,000 square kilometres of rainforest was felled every year, down from 3,000 square kilometres in the 1990s.

Simon Lewis, a reader in global change science at University College London and the University of Leeds, edited the series that included this report. He attributed the downturn to the lack of commercial agribusiness in the region. “Unlike in South America or south-east Asia, in Africa we still see very little large-scale industrial deforestation for agriculture,” he said. “The decline of deforestation appears to be associated with countries obtaining revenue from mining and minerals and oil, rather than from large-scale agriculture expansion.”

Conflict in the DRC, which alone contains more than half of Africa’s forest cover, may also have contributed to the slowdown. “The reduction in deforestation is not because conservation initiatives have worked, or because the fight against illegal logging is won. It’s just that there has been less industrial activity as a result of the turbulence,” said Alexandra Pardal, an official at Global Witness, a UK-based campaign group. “As the region becomes more stable, there will be increased commercial interest to convert the forest for agriculture.”

Nonetheless, tree loss in the Congo basin is not being curbed as quickly as it is elsewhere. “There is a decrease but it is not that dramatic. It’s not the same reduction we see in the Amazon,” said Philippe Mayaux of the JRC, who led the group’s recent deforestation research.

Annual tree loss in the world’s largest rainforest peaked at 27,000 square kilometres in 2004, falling to 5,000 square kilometres by 2011, according to the US- based Climate Policy Initiative, which analyses climate and energy policies around the world.

And not everybody agrees that the rate of forest loss in the Congo basin is even declining. A 2013 paper from a team led by Belgian researcher Ernst Céline and published in Global Change Biology claimed that the annual rate of tree loss between 2000 and 2005 was in fact double that in the decade to 2000.

Environmental advocacy group Greenpeace also contests the JRC’s findings. “Most recent research as well as our field experience indicates that deforestation and degradation rates are increasing, particularly in the DRC,” argued Greenpeace campaigner Danielle van Oijen.

The JRC’s research does not examine forest degradation–only full clearance–which explains part of the divergence, she explained. Cloud cover diminishes the reliability of remote sensing technologies, Ms van Oijen added, noting that Greenpeace relies more heavily on fieldwork.

Either way, it is clear that tree loss is a serious problem. If there was a slowdown between 2000 and 2010, it is not certain that it will endure.

Under slightly more stable political conditions, the DRC government issued hundreds of logging permits between 2010 and 2012, according to Global Witness. This trend is likely to continue as the region’s population grows and more companies seek profits in Africa.

Forest clearance in the Congo basin has increased again since 2010 and the future is not rosy, said the JRC’s Mr Mayaux. “Degradation and deforestation will increase because the population of these countries will dramatically increase,” he said. The number of people living in the DRC alone is expected to double to almost 150m by 2050, according to the UN.

“There is increasing demand for food and agricultural commodities and there is nowhere left to expand except for the rainforest,” Mr Lewis added.

Greenpeace and the World Resources Institute, a Washington, DC-based global research organisation, predict that forest degradation in the DRC will double this decade. Forest degradation refers to a reduction in forest quality, including the density and structure of trees as well as species diversity in plants and animals, according to the UN Research Institute for Social Development.

Investments in the palm oil sector could also contribute to stripping the Congo basin’s forests. Palm oil is used in products ranging from margarine to cosmetics. The region’s countries are trying to lure investors into the sector as they attempt to diversify their economies. Olam, the Singapore-headquartered agricultural processor, announced in 2012 that it would invest $250m in a Gabonese palm oil project, while Italy’s Eni is developing a multi-billion dollar project in the Republic of Congo. Feronia, a Canadian company, is reinvesting in existing palm oil plantations in the DRC.

Properly managed, those enterprises could create jobs and provide central African governments with revenues. Environmentalists, however, are concerned that establishing new plantations will lead to forest exploitation.

“It looks like central Africa may well go the same way as south-east Asia, developing huge expanses of oil palm plantations,” Mr Lewis said. “We may well now see a rapid increase in deforestation if we don’t control those commercial agricultural developments.”

In Cameroon, proposed palm oil developments by the US-owned Herakles Farms have proven controversial. Environmental campaigners, including Greenpeace and the World Wide Fund for Nature, protested against its plans to build a 73,000-hectare plantation–a space ten times the size of Manhattan–claiming that they violated local laws and could endanger wildlife and forest. In November 2013 the company received final approval to begin work on a slimmed-down plantation of 20,000 hectares, prompting another outcry from conservationists. Developing other industries could also lead to forest exploitation. In the DRC, oil, the kind that runs engines, tops that list. It is currently illegal to drill for crude in the country’s protected national parks, but draft legislation would give the government the right to override that ruling, opening the door for international oil companies to come into the forest, according to the UN’s cultural agency (Unesco) and the World Bank. First among those investors would be London-based Soco International, which has a licence to explore a block overlapping Virunga National Park, a Unesco world heritage site and one of the last remaining habitats of endangered mountain gorillas.

Illegal logging is another major concern, particularly in the DRC. A March 2013 Greenpeace report found the country’s logging sector in a state of “organised chaos” because investors routinely flout a 2002 ban on new industrial logging permits. “It’s a free-for-all in the DRC,” Ms van Oijen said. “Chinese, Malaysian, Lebanese and European companies are looking for commercial timber, and the Congo is one of the last forest landscapes where you can still find interesting amounts, so they are finding illegal ways to get it.” Greenpeace research suggests that some companies are circumventing the moratorium by illegally using artisanal permits, designed only for small-scale forestry by local populations. Others are operating without any licence at all. In a country where corruption is rife, logging groups can “negotiate almost anything”, Ms van Oijen noted. Most of the region’s illegal loggers are targeting an endangered tree species called wenge, a valuable hardwood coveted in China where it is used to make flooring and furniture. Its removal in the DRC is rampant, according to a July 2012 Greenpeace study. “Wenge grows in clumps and logging companies come in with an illegal permit or no permit at all, log it all out, and destroy the forest,” she observed. As the forests shrink, local wildlife is disappearing. “The Congo basin has more biodiversity in terms of big fauna than in the Amazon, and for the moment what we observe is the destruction of the habitat, which is problematic for many species,” Mr Mayaux said. The population of central African forest elephants, for instance, is estimated to have fallen by over 60% since the turn of the century, as the landscape opens up to poachers, according to the African Wildlife Foundation, a US-based conservation organisation. In the DRC, where it once thrived, this unique species has been hunted almost out of existence.

Deforestation also poses a problem for climate change. The region’s carbon stock represents about 25% of the world’s total. Tree loss is one of the biggest sources of carbon dioxide warming the atmosphere. “As it goes on you will have significantly less rain and farmers in the Congo basin will be affected,” Ms van Oijen explained. The chaos in the logging sector is not only accelerating tree loss, it is also depriving governments of tax income. An October 2013 Global Witness report found that the DRC lost 90% of its logging revenues the previous year to tax dodgers. New European Union legislation implemented in March 2013 offers the logging sector a glimmer of hope. Companies are now banned from selling illegally harvested timber or products made from illegal wood on the EU market.

This law also includes Voluntary Partnership Agreements (VPAs), deals negotiated with producer countries to help tackle illegal logging. The US implemented similar laws in 2008 and together they could help dry up markets for illicit timber. EU companies will face stiff penalties if they breach the new laws, but enforcement is still a challenge. “EU and US authorities have been extremely slow in enforcing their legislation and it’s a worry,” Ms Pardal said. “As things stand, Europe still has an open-door policy to illegal timber imports from the Congo basin.”

For countries in the region, balancing the demands of fast-growing populations with responsible forest management is a complex task. The VPAs may help by giving logging transgressions a higher priority. In Liberia, for instance, the agreement enabled the government to take action against the wide-scale abuse of private-use permits, according to the UK Department for International Development.

All of the Congo basin countries are signatories of the Convention on Biological Diversity, a legally binding global agreement signed in Rio de Janeiro in 1992. Under this treaty the countries agreed to protect 17% of their land. But at a nationwide level, there is little evidence of coherent land management.

The EU’s legislation should help, but it will require African governments to do their part, too. “What countries need is a sustainable land-use policy, but this is something that none of them have yet,” Ms Pardal said. “There is a fundamental problem of corruption and governance and the decision-making around forest management has been perverted. If you have deforestation and the serious degradation we are seeing now, you won’t have the water, the protein, or the resources that their populations need to survive.”