The direct and indirect effects of afforestation on climate forcing at high latitudes and their relative magnitudes over the lifetime of a plantation. a) Plantation establishment disrupts the previously intact soil,
leading to increased decomposition of microbial carbon (1), which is exacerbated by enhanced soil insulation caused by increased snow trapping and reduced snow packing (2). Growing trees exude carbon from their roots accelerating the turnover of soil carbon by root-associated microbes (3). As the plantation matures, trees darken the surface and diminish the proportion of energy reflected to the atmosphere (4). When a plantation is disturbed, the albedo increases while carbon stored in biomass decreases (5). Credit: Laura Barbero-Palacios, Greenland Institute of Natural Resources
In addition, the regions surrounding the North Pole in North America, Asia, and Scandinavia are prone to natural disturbances – such as wildfires and droughts – that kill off vegetation. Climate change makes these disturbances both more frequent and more severe.
The researchers say that tree planting at high latitudes is a prime example of a climate solution with a desired effect in one context but the opposite effect in another.
The Net Climate Impact (NCI) of tree planting across the Northern circumpolar region (blue=cooling, red=warming). NCI is the carbon storage in trees minus the albedo reduction effect expressed as CO2 equivalents (CO2e) per unit area. CO2e indicates the mass of CO2 that would need to be emitted/extracted from to the atmosphere to force a similar warming/cooling effect. Note that significant areas of the Arctic are excluded due to lack of data. Given the general northward change from cooling to warming effects, the researchers expect these areas to show mainly warming net effects.