Composition diversification vs. structure diversification: How to conciliate timber production and carbon sequestration objectives under drought and windstorm risks in forest ecosystems

Forests provide ecosystem services such as timber production and carbon sequestration. However, forests are sensitive to climate change, and financial and amenity losses are expected for forest owners and society, respectively. The forests in the Grand-Est region, France, are dominated by European beech, for which a decline is anticipated due to repeated drought events induced by climate change. These forest ecosystems are also threatened by windstorm events. Beech forests need to adapt and diversification can decrease drought and windstorm risks. In this context, the objective of the paper was to compare different forest adaptation strategies from an economic perspective with the objective of reducing drought- and windstorm-induced risks of dieback. For this purpose, we studied two types of diversification that we analysed separately and jointly: Mixing beech with oak and diversifying stand structure (i.e. from an even-aged to an uneven-aged forest). We also considered two types of loss (financial, and in terms of carbon sequestration) under different recurrences of drought and windstorm risks. We combined a forest growth simulator with a forest economic approach through the computation of land expectation value (LEV). Maximizing the LEV criterion made it possible to identify the best adaptation strategies in economic terms. The results show that diversification increases timber production and LEV, but reduces carbon storage. The two risks as well as the adaptation strategies show some synergies. Finally, trade-offs between the financial balance and the carbon balance (i.e. adaptation vs. mitigation) are possible.