Mixed forest plantations for climate change mitigation and adaptation - MixForChange

Abstract

Forest restoration and afforestation with native tree species has therefore recently received a wide international attention as a crucial opportunity for mitigating climate change (CC). Yet, the ongoing increase in biotic and abiotic stress driven by CC puts forests under threat. In the face of CC, adaptation and mitigation by forests are ultimately linked, because the ability of forests to sequester carbon (C) in the long run depends on the ability of tree species to cope with multiple stresses. A growing body of evidence suggests that mixed forest plantations, i.e., plantations where several tree species are mixed, may be more efficient in sequestrating C, while better coping with CC-related stress. Mixed plantations thus represent an important nature-based solution for CC mitigation and adaptation. However, monocultures still dominate the world's forest plantations. The reasons for the apparent aversion for mixed plantations among forest owners and decision makers need to be identified and addressed in future forest policies to promote the large-scale expansion of CC-resistant mixed forest plantations. One of the possible factor that may have prevented the expansion of mixed plantations at large scales is an insufficient scientific evidence base for decision makers. Using an existing global network of forest biodiversity experiments (TreeDivNet), we will provide a mechanistic understanding of how tree diversity, species identities and management (thinning and fertilization) influence the potential of mixed forest plantations to mitigate (C sequestration) and adapt (drought resistance) to CC. In addition, we will translate this knowledge into recommendations and guidelines for forest managers and policy-makers. The design of TreeDivNet experiments allows detection of causal relationships between tree diversity, management (incl. thinning and fertilization) and forest ecosystem functioning (incl. C sequestration). This mechanistic understanding and the contrasting environmental contexts embedded in the global network of TreeDivNet experiments will allow us to scale-up our findings beyond case studies to provide evidence-based guidelines for mixed plantation management in a broad range of environments. Moreover, MixForChange will analyse in a common framework, and at unprecedented scale, synergies and trade-offs between the CC mitigation and adaptation potential of mixed plantations and the fulfillment of stakeholders' objectives. This - currently missing - science base is a prerequisite to the large scale implementation of mixed plantation, which require both technical knowledge and acceptance by forest owners and stakeholders. The societal impact of MixForChange will be ensured by a strong focus on knowledge transfer and capacity-building at all levels of forest-policy and management decisions. Doing so, MixForChange will make an important contribution to promoting mixed forest plantations as nature-based solutions to fight CC. (AU)