According to fieldwork from south-central Sichuan Province, biodiversity within monocultures is lower than within cropland, the very land being restored.
The research found that cropland restored with mixed forests offers marginal biodiversity gains and comes at no economic cost to households, relative to monocultures.
The researchers recommend incentives for restoration of native forests under the program, which they say would provide the greatest benefits for biodiversity.
The world’s largest reforestation scheme may offer only marginal benefits for — or diminish — biodiversity, a study released earlier this month in Nature Communications revealed.
A team of international researchers led by Princeton University found that the overwhelming majority of forests restored under China’s Grain-for-Green program – which amount to roughly 28 million hectares – are monocultures or compositionally simple forests.
This spells bad news for biodiversity, the study shows, in a country already experiencing severe wildlife population declines.
Through fieldwork in south-central Sichuan Province, the researchers determined that restored monocultures support fewer species of birds and bees – common indicators of biodiversity – than sloped cropland, the very land targeted for restoration. Even mixed forests – those restored with two to five tree species – offer only marginal benefits for birds and harbor less bee diversity than cropland.
But there is still a case for optimism, the authors emphasize. Choosing mixed forests over monocultures results in a net gain in bird diversity, with no penalty for bee diversity. Switching to mixed forests is also unlikely to pose significant economic risk to rural households, highlighting the potential for biodiversity gains that the Grain-for-Green program has yet to realize.
Conceived in the wake of historic floods of 1998 – which left around 4,000 dead – China’s Grain-for-Green program (GFGP) is a government-led effort to reduce soil erosion, mitigate flooding, and alleviate rural poverty through restoration. Households receive cash and food payments, in addition to technical support, to restore sloped cropland and scrubland – areas that are prone to landslides and erosion. The forests restored under GFGP — covering an area larger than New Zealand — comprise the largest national undertaking of reforestation in the world.
China’s reforestation programs like Grain-for-Green are part of the country’s efforts to reduce deforestation and restore areas already affected. According to the UN’s Food and Agriculture Organization (FAO), only 6 percent of China still contains primary forest, and satellite data show that areas of primary forest connected and undisturbed enough to support their original biodiversity levels — called Intact Forest Landscapes (IFLs) — are nearly gone. In total, China’s Natural Forest Conservation Program aims to reforest 40 million hectares by 2020.
Most forests under GFGP are production forests, harvested for timber, tree fruits, and other cash crops, with biodiversity restoration as a secondary concern. Nonetheless, the profound scale of the program suggests that it will have a considerable impact on biodiversity, an issue that, the authors write, is “strikingly unexplored.” Until now.
The team of academics – hailing from Princeton, the Chinese Academy of Sciences, Sichuan University, the University of East Anglia, and the University of Vermont – came together to explore, for the first time, the biodiversity implications of the program.
“We asked: What types of forest are being established by the program across China?” said lead author Fangyuan Hua, a postdoctoral research associate at Princeton, in a press release. “Then, focusing on a particular region, we asked: How does the biodiversity of the new forests compare to the biodiversity of the croplands they are replacing? How do the new forests compare to native forests? And, would planting more diverse forests result in any biodiversity benefits while also being economically feasible?”
In a review of 258 publications on the composition of GFGP forests across China, the authors found that the overwhelming majority of restored forests under the program are monocultures — forests comprised of a single tree species, such as Japanese cedar, eucalyptus, or bamboo. “Mixed forests” with between two and five species were less common. Only three publications cited locations where forests were restored to approximate the native landscape.
“To our knowledge, this is the first nationwide synthesis of the tree-species composition of forests reestablished under the program,” Hua said. “This is essential to understanding the program’s biodiversity implications.”
But how does biodiversity fare among the different restored forest types?
To answer this question, the team carried out fieldwork in south-central Sichuan Province. They studied the diversity and composition of birds and bees within restored monocultures and mixed forests, cropland the forests were replacing, and native forests.
“Birds are sensitive to the types of trees, the overall age of the forest and the insects within the forest, and bees depend more on resources like pollen or nectar from the understory,” Hua said. “Together, these two taxa provide a well-rounded picture of biodiversity within a forest.”
Their results revealed some surprising trends. Sichuan forests restored with monocultures — the vast majority of forests under the program — sustained fewer species of birds and bees than cropland – the very area targeted for restoration. The results were even bleaker for bees, which exhibited lower diversity in both monocultures and mixed forests, relative to cropland. As expected from previous research, native forests had higher bird and bee diversity than any other habitat type.
“None of the restoration techniques are really going to produce major improvements on biodiversity,” co-author David Wilcove, professor of ecology and evolutionary biology at Princeton, told Mongabay. “You can make some improvements by planting mixed forests, but that won’t benefit the bees and the other pollinators.”
There is a bright side, however, the authors point out. Choosing mixed forests over monocultures offers biodiversity gains – an increase in bird diversity – without a noticeable change in bee diversity. Mixed forests are also likely to offer better erosion control, carbon sequestration, and resilience to pest outbreaks, the study reports, making them a more appealing option for restoration from an environmental perspective.
But what about from an economic perspective?
The final component of the study addressed this question. Through a series of semi-structured interviews in villages surrounding their field sites, the authors investigated whether or not planting mixed forests or native forests in lieu of monocultures posed economic risk – termed an “opportunity cost” in the paper – to the rural households responsible for the planting.
Their data revealed the two forest types are effectively the same, in economic terms. Profits from forest products and intensity of labor was comparable between monocultures and mixed forests, indicating that a shift to mixed forests “is unlikely to carry opportunity costs or pose unforeseen economic risks to households,” the authors state in the paper.
The analysis also revealed the opportunity to restore native forests with limited financial tradeoffs. According to its findings, even if there is no financial return from forest products the opportunity cost would only constitute 12.8% of household income ($431 per hectare per year).
“This is a relatively small percent,” Wilcove told Mongabay. “For a somewhat modest payment on the part of the government to the family you could make up for that loss of income” and restore the landscape with native forests.
Hua agrees: “If the Chinese government is willing to expand the scope of the program, restoring native forests is, without doubt, the best approach for biodiversity.”
But the authors say there is still plenty of room for improvement within the constraints of China’s existing incentives and policies by choosing mixed forests over monocultures.
“Even within the current scope of the program, our analysis shows there are economically feasible ways to restore forests while also improving biodiversity,” Hua said. “Together, our findings point to the enormous potential of biodiversity benefits that China’s Grain-for-Green Program has yet to realize.”
China has committed to extend GFGP to 2020 and plans to restore an additional 2.83 million hectares of marginal cropland. But whether this area is turned into monocultures, mixed forests, or native forests remains to be seen – as does the outcome for biodiversity.
Wilcove’s suggestion? “Go native! Look for opportunities to restore native forests. Those forests would be best for biodiversity.”
Hua, F., Wang, X., Zheng, X., Fisher, B., Wang, L., Zhu, J., … & Wilcove, D. S. (2016). Opportunities for biodiversity gains under the world’s largest reforestation programme. Nature Communications, 7.