In news that will be of interest to those companies planning to offset carbon-equivalent emissions through the planting of forests, two separate recent papers in Nature Sustainability have suggested that planning for afforestation must be very carefully carried out. One paper looked at the effect of subsidised tree planting in Chile between 1974 and 2012; in some cases, native forests were replaced by new planting because of poor bureaucracy, and although total forest cover in the country increased, native forest cover decreased. The monocultures that are often the product of tree planting schemes meant that biodiversity decreased, as did the amount of carbon stored in forests. “If policies to incentivise tree plantations are poorly designed or poorly enforced, there is a high risk of not only wasting public money but also releasing more carbon and losing biodiversity,” was the conclusion of co-author Prof Eric Lambin of Stanford University.

The other paper examined the effect of soil conditions on the uptake of carbon dioxide by trees. In carbon-poor soils, planting of forests increased the carbon density of the soils, but in carbon-rich soils, the carbon density of the soil decreased as forests were planted. Lead author Dr Anping Chen of Colorado State University said of the findings that the authors “hope that people can understand that afforestation practices are not one single thing” – i.e. that those planning on using forestry to offset emissions will have to consider carefully local conditions, and account for their carbon accordingly.