Forest ecosystems are reservoirs of biodiversity and provide many services to people and society (e.g. edible plants, carbon storage, wood, cooling during the summer, etc.). Until now, these services have always been quantified for forest interiors, far away from forest edges as they are subject to all kinds of edge effects and external influences. However, due to forest fragmentation, there are now many more forest edges: no less than 70% of the European forest area is located within 1 km of a forest edge! It is therefore important to quantify ecosystem services also in forest edges and to compare them with forest interiors.

In this paper, we quantified and compared four biodiversity indices (total number of plant species, number of forest specialists, functional diversity and phylogenetic diversity) and seven ecosystem services (soil carbon storage, pollination value, cooling during summer, nutrient cycling, edible plants, wood production and rejuvenation of the forest) between forest edges and forest interiors. Data was gathered from 45 oak-dominated forests in different European countries (Italy, Switzerland, Germany, Belgium, France, Poland, Sweden, Norway), and realized through collaboration with local universities in the respective countries. These universities are part of the umbrella network FLEUR (https://fleur.ugent.be), and funding was provided through the European Union via the Forest Microclimate Assessment project FORMICA (https://formica.ugent.be).

Our main finding was that some ecosystem services are higher in the forest edge, while others are higher in the interior. Forest edges harbor more plant species in total, have a higher wood production, provide more nectar to pollinators and show a better rejuvenation of the forest. Forest interiors, on the other hand, contain relatively more forest specialist plants (e.g. bluebells, wood anemones, wild garlic, etc.), have a higher phylogenetic diversity (plant species are better distributed on the evolutionary tree and the plant community is therefore more robust to changes in itsenvironment), offer more cooling during the summer and are better at cycling nutrients. On a landscape scale, it is therefore important to have sufficient forest edge and forest interior area, as these can be complementary in providing as many ecosystem services as possible. The importance of forest edges should thus not be ignored in policy and conservation decisions for our European forests.

In addition, we found that forest structure is the most important driving factor of these differences between forest edge and forest interior. Forests with a more diverse, complex structure are better at simultaneously providing multiple services. Forest structure, or in other words the architecture of the forest (for example, the stratification and density of the canopy), and can be strongly determined by management. Foresters can use their management to determine which ecosystem services they want to maximize in their forest, or they can also choose to have as many services as possible provided at the same time. Diversification is again of key importance here: a forest with a complex structure, and therefore a combination of more open and more closed parts (possibly even interspersed with small open areas), will likely be the “healthiest” forest and best at simultaneously providing many different services.

Cover picture: ©Pieter-Jan D'Hondt