Forest restoration, biodiversity and ecosystem functioning

Abstract

Globally, forests cover nearly one third of the land area and they contain over 80% of terrestrial biodiversity. Both the extent and quality of forest habitat continue to decrease and the associated loss of biodiversity jeopardizes forest ecosystem functioning and the ability of forests to provide ecosystem services. In the light of the increasing population pressure, it is of major importance not only to conserve, but also to restore forest ecosystems. Ecological restoration has recently started to adopt insights from the biodiversity-ecosystem functioning (BEF) perspective. Central is the focus on restoring the relation between biodiversity and ecosystem functioning. Here we provide an overview of important considerations related to forest restoration that can be inferred from this BEF-perspective. Restoring multiple forest functions requires multiple species. It is highly unlikely that species-poor plantations, which may be optimal for above-ground biomass production, will outperform species diverse assemblages for a combination of functions, including overall carbon storage and control over water and nutrient flows. Restoring stable forest functions also requires multiple species. In particular in the light of global climatic change scenarios, which predict more frequent extreme disturbances and climatic events, it is important to incorporate insights from the relation between biodiversity and stability of ecosystem functioning into forest restoration projects. Rather than focussing on species per se, focussing on functional diversity of tree species assemblages seems appropriate when selecting tree species for restoration. Finally, also plant genetic diversity and above - below-ground linkages should be considered during the restoration process, as these likely have prominent but until now poorly understood effects at the level of the ecosystem. The BEF-approach provides a useful framework to evaluate forest restoration in an ecosystem functioning context, but it also highlights that much remains to be understood, especially regarding the relation between forest functioning on the one side and genetic diversity and above-ground-below-ground species associations on the other. The strong emphasis of the BEF-approach on functional rather than taxonomic diversity may also be the beginning of a paradigm shift in restoration ecology, increasing the tolerance towards allochthonous species.

Figure 1

Seedling planting and ecological forest restoration. Planting late-successional tree species under early-successional shrubs can be an effective means of restoring forests under high abiotic stress. Tree planting under facilitating nurse shrubs is a typical example of the community approach to forest restoration. This figure shows the planting of an African wild olive seedling (Olea europaea ssp. cuspidata) under the canopy of Euclea racemosa rather than in the open space between the present shrubs. See [43] for details. Tsegaye Gebremariam, Raf Aerts and Bisrat Haile agreed to be photographed in the field.

Figure 2

Related concepts in the scientific literature on forest restoration, biodiversity and ecosystem functioning. The relationship between the most widely used words (30 of 2745 terms) in the abstracts of scientific literature on forest restoration, biodiversity and ecosystem functioning (BEF). Data were obtained from Thomson Reuters Web of Science using the query Topic = (biodiversity ecosystem function*) refined by Topic = (restoration) AND Topic = (forest*). The diagram shows that, even in the BEF literature, functional (bio)diversity has received less attention than species richness and (plant) species diversity thus far (an interactive online version shows the number of occurrences for each word and word pair and the contexts of each word pair and is available at http://www-958.ibm.com/v/116799).