It is widely assumed that land uses that increase carbon in biomass and soil to mitigate climate change also benefit biodiversity. But that might not always be the case. Until recently, there was no clear picture on what the most likely carbon-boosting strategies, such as planting trees in open lands and halting deforestation, meant for biodiversity.

In response, scientists from the Center for International Forestry Research (CIFOR) and partner organizations decided to study the relationship between payments for adding ecosystem carbon and the level of biodiversity in 12 landscapes across seven countries –Finland, Indonesia, Mexico, Laos, Peru, Tanzania and Vietnam.

“We wanted to understand the impact of the most common ways of increasing carbon in practice, because it might not always follow the general trend,” says lead author and associate professor with Peking University Markku Larjavaara. “Take the plantation of one single exotic tree species on native shrubland: that is set to augment carbon, but not biodiversity, even if these aspects go hand in hand in the landscape as a whole.”

To that end, researchers conducted two sets of interviews. In one case, they asked 97 experts how land use would change from the business-as-usual scenario with hypothetical annual payments of US$ 1 and US$ 10 for every additional ton of stocked carbon.

Then, they asked 115 biodiversity experts to rate how beneficial those land uses would be for local species of animals, plants and fungi in each of the landscapes –most specialists were focused on only one of the landscapes.

A win-win for climate and conservation

The research confirmed that more carbon generally means more biodiversity and the other way around, as researchers expected. “As a first guess, one can assume that something which is bad for carbon, such as agricultural subsidies, is bad for biodiversity as well,” says Larjavaara.

Interestingly, scientists also found that all the suggested main strategies to increase ecosystem carbon were beneficial for biodiversity –in nearly all cases. In Finland, Laos, Mexico and Vietnam, for instance, specialists expected carbon payments to stimulate increase of carbon in already forested areas.

Other mechanisms that were found to increase both carbon and biodiversity are tree-planting in agricultural lands (Peru, Tanzania); converting agricultural lands into natural forests (Peru); and reducing decomposition and peat burning by planting trees in open degraded areas (Indonesia).

The archipelago of Zanzibar in Tanzania has the only landscape where the potential strategy of choice to increase carbon could be harmful to biodiversity. Specifically, some of the experts interviewed by researchers expected carbon funding to lead to the conversion of native coral rag scrubland into tree plantations.

The species that would be most impacted by these changes are the caffeine-free coffee species Coffea pseudozanguebariae, followed by the blue duiker (Cephalus monticola) and the shrub or small tree Xylotheca tettensis. The third most affected species would be the Zanzibar red colobus (‘Piliocolobus kirkii’) and the endangered Mafia Island toad (Stephopaedes howelli), both of them endemic.

Managing landscapes holistically

Scientists note there are two ways of increasing carbon relative to business-as-usual scenarios: slowing down its loss –for example, by protecting natural forests— and speeding its increase –for instance, by establishing planted forests. The first option is generally good for biodiversity, while the second might not, points out the study.

“Take a tropical rainforest: it might first be converted into pasture and then turned into forest again,” explains Larjavaara. “This new forest is likely to be much simpler, perhaps even a monoculture, meaning it will have a lot less biodiversity despite being a fairly good storage of carbon.” 

In light of the findings, authors call on policy-makers and land-use planners to take both carbon and biodiversity into account when making decisions on land use.

“Focusing in each of these aspects separately can lead to situations that make little sense, such as designating one area for biodiversity conservation and another for a carbon project,” says the scientist. “We could achieve much better results if both areas were managed for both biodiversity and carbon.”

The researcher hopes the study will open a path that others can tread and expand: “I really hope our study makes more people take both biodiversity and carbon into account when making decisions on land-use, rather than just blowing with the winds of markets.”