Adaptation of mountain forests management to climate change: can we maintain mixed uneven-aged and productive forests? | Adaptation des forêts de montagne aux changements climatiques: peut-on maintenir des forêts mixtes, irrégulières et productives ?

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN

International audience

English. Climate change is expected to increase exposure and vulnerability of forests ecosystems to natural disturbance or stresses, such as storms or droughts. Forest managers are investigating strategies to limit forest sensitivity to these risks. Some suggest increasing harvests and reducing diameter limit and/or stocking (i.e. basal area), so as to limit water competition and the amount of stock exposed to perturbations. However these practices could modify forests structures and compositions, whereas maintaining a continuous cover trough mixed uneven-aged stands is a primary issue in mountain forests, which have an essential protection function of human habitats against natural hazards (avalanches, landslides, rock falls…). Continuous cover forestry, which aims at increasing forests resilience trough settled regeneration and complementary species, could be a sustainable response to climate change. We decided to question whether these strategies (a more dynamic silviculture and continuous cover forestry) are compatible and sustainable. Our objective was to determine which management scenarios lead to satisfactory wood production while maintaining mixed and uneven-aged stands. We hypothesised that intermediate ranges of management would enable sustainable trade-offs between wood production, tree species diversity and tree size diversity. We propose a long-term simulation study based on Samsara2, a mountain forest simulation model developed for spruce-fir irregular forests of the French northern Alps, to analyse how production, diversity and structure respond to silviculture. We developed a silviculture algorithm to simulate management scenarios. We control harvesting parameters like harvesting and thinning diameters, minimal and maximal amount of harvest and its distribution among diameter classes. Stand responses to management are studied trough the Gini index applied to tree diameters, a species mixing rate, yield and harvested volume. A sensitivity analysis allowed us to determine the relative influence of algorithm parameters on the response variables as well as the domain where management objectives of wood production and adaptation to climate change reveal compatible. We present several examples of such scenarios that lead to a dynamic balance within a satisfactory range of irregular structure, species diversity, yield and wood production Although the current version of the model only takes two species into consideration, it covers a large range of the French northern Alps forests. Simulation models help understand stands response to alternative management scenarios and have thus a key role to play in the process of forest management adaptation to tackle climate change.