How tree planting works to combat climate change | Local news

“Trees can play a role in mitigating climate change for several reasons,” Bukoski said. “It's pretty easy to understand that forests pull and store carbon dioxide from the atmosphere, and trees are something pretty much everyone can support – we've introduced several bipartisan tree-planting bills in Congress. This study brings a nuanced perspective to the whole 'should we plant trees to combat climate change?' debate.”

Bukoski points out that global forest expansion is widely proposed as a key strategy to combat climate change, as forests sequester carbon dioxide from the atmosphere in their biomass and soils. Harvested wood also stores carbon in the form of wood products.

There are two basic approaches to expanding forests, said Bukoski.

“Basically, we can let the forests regenerate themselves, which is slow but cheap, or we can be more active and reforest them, which accelerates growth but is more expensive,” he said. “Our study compares these two approaches in reforestable landscapes in low- and middle-income countries and shows where natural regeneration or planting forests is likely to make more sense.”

Using machine learning and regression models, the scientists found that over a 30-year period, natural regeneration would be most cost-effective for 46 percent of the areas studied and planting for 54 percent.

They also concluded that a combination of the two approaches would be 44% better than natural regeneration alone and 39% better than planting alone in all areas.

“If your goal is to sequester carbon as quickly and as cheaply as possible, the best option is a combination of naturally growing forests and planting forests,” Bukoski said.

The study suggests that natural regeneration is particularly cost-effective compared to plantation agriculture in much of western Mexico, the Andean region, the southern cone of South America, West and Central Africa, India, southern China, Malaysia and Indonesia.

Conversely, plantations are preferable to natural regeneration in much of the Caribbean, Central America, Brazil, northern China, mainland Southeast Asia, the Philippines, and North, East and Southern Africa.

“Which method is more cost-effective at a particular location depends on several factors, including opportunity costs, relative carbon accumulation and harvest rates, and relative implementation costs,” Bukoski said.

Other scientists involved in the collaboration included Jonah Busch and Bronson Griscom of Conservation International, Susan Cook-Patton of The Nature Conservancy, David Kaczan of the World Bank, Yuanyuan Yi of Peking University, Jeff Vincent of Duke University, and Matthew Potts of the University of California, Berkeley.

The authors stress that reforestation is a complement, not a substitute, for reducing fossil fuel emissions. The total mitigation potential of reforestation over 30 years would amount to less than eight months of global greenhouse gas emissions, they note.

The authors add that carbon is only one aspect of growing trees. Biodiversity, demand for wood products, support for local livelihoods and non-carbon biophysical effects must also be considered when deciding where and how to reforest landscapes.

But they also point out that their findings suggest that reforestation offers far greater potential for cost-effective climate change mitigation than previously thought.

The results of the study, led by Conservation International, were published in Nature Climate Change.