Description of the Business As Usual (BAU)
Exploitation still relies too often on clear-cutting that exposes soils to high temperature and erosion, then increasing carbon exportation to the atmosphere and water. Rotation periods prime maximising short-term economic revenue. Management of the understory and of dead wood is not wise and ranges from excessive elimination, which reduces important resources for biodiversity and C sequestration, to excessive wood accumulation that can induce risk of pests and wildfires.
Description of the system change
Temperate European forests are accumulating carbon due to the combination of different factors, including forest immaturity after long-lasting exploitation, decreasing logging intensity, nitrogen deposition and CO2 fertilisation. Global warming has contrasting effects on C sequestration depending on latitude. In northern latitudes, rising temperatures are increasing the duration of the growing season, while in southern areas (mainly in the Mediterranean region) water availability is a limiting factor for plant growth and C sequestration.
Ideally, C sinks increase with forest age, the increase in the average diameter of trees and tree species richness. From the mitigation point of view, no exploitation is an efficient option to increase carbon sinks, since forests actively sequester atmospheric CO2 for very long periods after raising their maturity and because soil carbon stocks, which are more stable in time than plant carbon stocks, are more important in mature than in young forests.
However, social demands for other ecosystem services provided by forests make this option unviable at large scale. Diverse management options must be considered while preserving strategic forest patches for strict protection, in search of the best synergies between mitigation and adaptation strategies. It must be said that, when it comes to commercial forests, their mitigation capacity is primarily determined by species selection (slow-growing and dense wood trees), subsequent trade (e.g. wood treatment and distance to destination of the final product), and final use of the harvested wood (e.g. short- lived products as paper, firewood vs long-lived products such as construction, long lasting furniture, etc.).
In general terms, management makes forests carbon emitters in the short term but stimulates high productivity and therefore C sequestration in the mid-term, due to decreased competition. Moreover, cessation of exploitation and subsequent increase in forest density can be detrimental in water-limited regions, where water availability per tree can decrease to levels that induce growth decline, vulnerability to pests and increased mortality risk. In this sense, The Mediterranean basin is among the most threatened regions by climate change, with forecasted increases in drought severity and long-term aridity. These threats affect forests developed on poorly productive soils due to bioclimatic causes (natural restrictions for primary production) that interact with degradation induced by intense historical human pressure. In these forests, adopting adaptation strategies oriented to preserve the existing forest carbon stocks is a more realistic option than deploying carbon sequestration strategies with mitigation as the main objective.