Microbes in the bark of trees play an important role in removing methane from the atmosphere, scientists have discovered.
The greenhouse gas is a product of agriculture and the burning of fossil fuels and is 28 times more powerful than carbon dioxide. However, it remains in the atmosphere for a shorter time.
Since then, methane has been responsible for about 30% of global warming pre-industrial timeswith emissions currently rising at their fastest rate since the 1980s.
The team behind the study by the University of Birmingham, published in the journal Nature and led by Prof Vincent Gauci, investigated methane absorption levels in highland tropical forests in the Amazon and Panama; temperate broadleaf trees in Wytham Woods in Oxfordshire in the UK; and boreal coniferous forest trees in Sweden.
Methane absorption levels were found to be highest in tropical forests, likely due to the microbes’ ability to thrive in warm and wet conditions.
Previously, soil was thought to be the only terrestrial sink for methane, with soil bacteria able to absorb the gas and break it down to use as an energy source. But Gauci said the research highlighted “a remarkable new way in which trees provide an essential climate service”.
Launched at the Cop26 climate summit in 2021, the Global Methane Pledge set out the goal of reducing methane emissions by 30% by the end of the decade. Gauci said: “Our results suggest that planting more trees and reducing deforestation should certainly be important parts of any approach to this goal.”
Tree planting has become a key tactic in combating the climate crisis, with the British government plans to spend more than £500m on trees and woodlands between 2020 and 2025. But another piece of research published on Wednesday shows countries need to weigh the benefits and disadvantages of tree plantingwith natural forest regeneration proving more cost-effective in some circumstances.
Jacob Bukoski, a scientist from the Oregon State University College of Forestry, and his team analyzed data from thousands of reforestation sites in 130 countries for the study, published in the journal Nature Climate Change. They found that natural regeneration would be the most cost-effective over a 30-year period for 46% of the areas studied, while planting would be more cost-effective for 54%.
“In general, we can let forests regenerate on their own, which is slow but cheap, or take a more active approach and plant them, which accelerates growth but is more expensive,” Bukoski said. “Our study compares these two approaches across reforestable landscapes in low- and middle-income countries, and identifies where naturally regenerating or planting forests is likely to make more sense.”
Natural regeneration has been found to be more cost-effective in areas such as western Mexico, the Andes region, the southern cone of South America, western and central Africa, India, southern China, Malaysia and Indonesia.
A combination of factors favored natural regeneration in these areas, such as whether there were sufficient ecological conditions for tree regrowth, opportunity and implementation costs, and carbon accumulation rates.
Scientists eventually determined that using a combination of both approaches globally would be 44% better than natural regeneration alone and 39% better than just planting. “If your goal is to sequester carbon as quickly and as cheaply as possible, the best option is a mix of both natural regenerating forests and planted forests,” Bukoski said.
While reforestation can be highly effective in offsetting greenhouse gas emissions, the authors emphasize that reforestation is a complement to, not a substitute for, reducing fossil fuel emissions. The entire mitigation potential of reforestation over 30 years would only equal less than eight months of global greenhouse gas emissions.
The authors also argue that many other factors need to be considered alongside carbon when deciding where and how to reforest landscapes, such as reforestation’s impact on biodiversity, demand for wood products and non-carbon biophysical effects such as water availability.
