|The ghost orchid is very vulnerable to clear-cutting (Photo: BM)|
When a forest is clear-cut, the soil is disturbed, root systems die and the soil leaks carbon for 10-20 years before photosynthesis from new plants compensates for the leakage. The powerful greenhouse gas methane is emitted as well from clear-cuts. It can take up to 40 years for trees planted on drained peat land until they act as a net carbon dioxide source. If the forest is harvested after 80 years and if the biomass is used to produce paper with a short life span, the forest ecosystem becomes a major greenhouse gas source.
In continuous cover forestry, where the soil is never left bare, more of the carbon and nutrients remain bound. Because of this more carbon is stored in such forests and they yield more ecosystem services over all. Other research does not find a significant difference between in carbon sequestration between clear-cutting and continuous cover forestry, but these authors did not consider the increased soil carbon fluxes after clear-cutting or that in practice branches and treetops are removed for bioenergy. A recent review that summarizes on carbon sequestration concludes that managed forest lose soil carbon in the long run.
A less intensive management may reduce the risk of warming climate effects. Functional ecosystems resist and recover better from fires, storms, insect outbreaks and other damage, compared to fragmented and managed areas. Furthermore, a large variety of mycorrhiza fungi store more carbon in the soil.
More carbon is sequestered in mixed forests than in pine monocultures according to modelling - but also empirical studies. Deciduous forests have higher albedo than dark and dense coniferous forests, and reflect more sunlight back into space while coniferous trees absorb more heat. The evapotranspiration of the deciduous canopies (the transport of water into the atmosphere through transpiration from the vegetation, especially during the summer) results in local cooling and possible cloud formation that could increase albedo. Replacing natural ecosystems with monoculture forest plantations can increase runoff and reduce evapotranspiration. Clear-cuts lead to larger local variation in temperature and an increase in air temperature during summer months.
Clear-cutting is the dominant forestry method in Sweden, for both historical and economic reasons. But there are many ways to compute profitability - which method one should choose depends on one's purpose. When natural regeneration is taken into account in economic calculations (which spares the cost of planting), continuous cover forestry becomes more profitable in most cases.
Continuous cover forestry has large advantages for biodiversity. In other parts of Europe, for instance in the United Kingdom and Italy, a transition to continuous cover forestry has therefore begun. That means much practical knowledge is available on how a transition to this form of forestry benefits both the climate and biodiversity and simultaneously takes social considerations into account. In the entire world, there is approximately 2 billion hectares of land that could be restored to natural forests in different ways, in order to support multiple ecosystem services from forests.