"Climate change and forest ecosystems are closely connected, with climate mainly affecting the rate, frequency, intensity and timing of air temperature, solar radiation and rainfall. Climate change impacts can be both positive and negative on forest structure, growth patterns, composition, productivity and functioning, depending on the location and type of forest. For example, positive effects are expected, in Europe, on wood production and wood supply, especially at high latitude, due to enhanced CO2 concentration in the atmosphere and more rainfall. However, climate change could represent a threat for forest ecosystems and services, especially in Mediterranean regions, where higher rates of tree mortality and forest fires, due to enhanced temperatures and droughts conditions, are expected to increase (EEA, 2016a; 2016b). Modified climate conditions have already led to negative impacts such as changes in: forest species composition and biodiversity, growing rate, resistance to pest and disease, invasive species propagation, forest fire regime and forest susceptibility to fire.
Forests can act as carbon sink; they can accumulate atmospheric CO2 as carbon in vegetation and soils. However, human activities affecting land use and forestry characteristics can alter the carbon cycle between the atmosphere and the terrestrial ecosystems leading to more CO2 emissions. Since forests are able to act as carbon sink, they are included in international policies (EU LULUCF Regulation 2018/841) to address climate change both via mitigation and adaptation processes; linking these two aspects should be preferred.
Afforestation and reforestation projects can pursue this double role for forest ecosystems. Afforestation (i.e. converting long-time non-forested land into forest) refers to the establishment of forests where previously there have been none, or where forests have been missing for a long time (50 years according to UNFCCC) while reforestation refers to the replanting of trees on more recently deforested land (i.e. converting recently non-forested land in forest). If these two approaches are viewed as complementary, they may enable “win-win” policy options. However, if unsustainably managed, both practices may be controversial as they may lead to the destruction of original non-forest ecosystems (e.g. natural grassland).
At international level, afforestation and reforestation have been initially recognized as mitigation approaches, and have been promoted for carbon sequestration goals. However, they can also help forests to adapt to climate change by decreasing human pressures (for example by reducing the destruction or degradation of habitats) and enhancing landscape connectivity and reducing fragmentation (thus facilitating species migration under climate change conditions). Afforestation and reforestation may also contribute preserving biodiversity hotspots, avoiding soil degradation and protecting other natural resources (e.g. water).
The sustainable management of afforested or reforested land help in pursuing adaptation responses, since it maintains forests status and guarantees ecosystems services, especially at local scale, by reducing vulnerability to climate change and to biodiversity loss. In case of crop failure due to climate change, forests can provide safety nets for local communities with their products (e.g. with both wood or non-wood products, such as game animals, nuts, seeds, berries, mushrooms, medicinal plants). Forests also help in regulating water flow and water resources through their hydrological-related ecosystem services (e.g. base flow conservation, storm flow regulation and erosion control). In addition, planting trees can create new habitats for more tolerant species and enhance biodiversity, especially when multispecies plantations (choosing native species and avoiding invasive ones, less adapted to the habitat) are preferred. Afforestation and reforestation can also control soil degradation, hydraulic and landslide risks and encourage local communities towards agroforestry or silvo-pastoral systems, thus creating new income opportunities. Finally, forest management practices, such as sanitation harvest, can help in reducing pests and diseases attack.
Through the Agenda 2000 programme, afforestation was intended as an accompanying measure of the agricultural policy. The EU afforestation policies have supported the planting of about 2 million hectares of trees on agricultural land in the period from 1994-2015. However, the level of afforestation has decreased over the last decades although afforestation is currently considered as a mitigation strategy by CO2 sequestration. The current allocation in the EU Rural Development programs (2014-2020) expects the planting of further 510 thousand hectares.
There is not enough information available to estimate the share of coniferous species versus broadleaved species in afforestation and reforestation programmes. Nevertheless, the share of the broadleaved and mixed forests has been increasing in Europe in the latest decades even if afforestation with conifers is still dominating in some countries."