Assessment of the adaptive capacity to climate change of forest social-ecological systems

Impacts of climate change are likely to be marked in areas with steep climatic transitions. Species turnover, spread of invasive species, altered productivity, and modified processes such as fire regimes can all spread rapidly along ecotones, which challenge the current paradigms of ecosystem management. We conducted a literature review at a continental-wide scale of South-Western European forests, where the drier and warmer conditions of the Mediterranean have been widely used as examples of what is expected in more temperate areas. Results from the literature point to: (a) an expansion of slow-growing evergreen hardwood trees; (b) increased dieback and mortality episodes in forests (both natural and planted) mostly related to competition and droughts, and mainly affecting conifers; and (c) an increase in emergent diseases and pests of keystone-trees used in agroforestry zones. There is no consensus in the literature that fire regimes are directly increasing due to climate change, but available satellite data of fire intensity in the last 17 years has been lower in zones where agroforestry practices are dominant compared to unmanaged forests. In contrast, there is agreement in the literature that the current spread of fire events is probably related to land abandonment patterns. The practice of agroforestry, common in all Mediterranean countries, emerges as a frequent recommendation in the literature to cope with drought, reduce fire risk, and maintain biodiverse landscapes and rural jobs. However, it is unknown the extent to which the open vegetation resulting from agroforestry is of interest to forest managers in temperate areas used to exploiting closed forest vegetation. Hence, many transitional areas surrounding the Mediterranean Basin may be left unmanaged with potentially higher climate-change risks, which require active monitoring in order to understand and help ongoing natural adaptation processes.

Forest social-ecological systems (FSESs) can play a major role in both the mitigation of climate change, as well as the adaptation of local communities to it. In Europe, however, forests are highly fragmented and located close to human populations. This means that maintaining forest sustainability implies not only increasing ecosystem adaptation but also developing social adaptation. Hence, there is a need to understand the current priorities and management goals of forestry stakeholders, as well as their capacity to achieve functional and sustainable FSES in the future. The present study uses an interdisciplinary approach to evaluate stakeholders’ capacity to deal with climate change and top-down policies in different FSESs. We selected five FSESs in France that exhibit a range of climatic threats and socio-economic characteristics to estimate their adaptive capacity and transformative potential. The estimation is based on an assessment of different types of capital (i.e. natural, social, resources, governance) that involves evaluating 70 indicators through more than 70 semi-structured interviews with local stakeholders. Our results highlight that forest management in France, and more broadly in Europe, is mainly based on technical approaches, which build stakeholders’ confidence in their capacity to maintain the status quo. We observe asymmetry in capital distribution in some FSES, mainly through the maximization of the resources capital, which can constraint FSESs in a robustness trap. To develop adaptive capacity for small perturbations as well as transformability, forestry stakeholders should be encouraged to compromises. More balanced capital distribution, with decreased economic benefits, along with new technical approaches and changes to the landscape composition could be necessary to ensure the long-term adaptability of FSES to climate change.

In a climate change context, the implementation of adaptive strategies appears as one of the greatest challenges for our societies. At the beginning of the 21st century, the scientific community proposed an adaptation option to limit climate change impacts on biodiversity, the assisted migration (AM). Despite a good theoretical justification, the AM application raises several questions about ecological, economical, ethical and political issues. Along this thesis, I was interested in the adaptive capacity of society actors concerning the changing climate, through the implementation of new practices as AM. Given the slow migration capacity of tree species, forests represent a relevant ecosystem for AM application, especially in France which has more than 29% of its surface as forest areas that are highly fragmented. In the first part of this thesis, I concentrated on the AM debate and I analyzed the actual barriers in its conception and its implementation. On the basis of a comparative analysis between France and Canada, I highlighted that different acceptations of adaptation and AM between policy and scientific actors represent a barrier for the implementation of adaptive strategies, as AM. Hence, I proposed a new concept of AM at the ecosystem scale, allowing limiting the focus on economic issues of AM programs. Moreover, I demonstrated that the AM actions are not constrained in a precautionary approach but could be applied in a prevention context. These results unties the deadlock about the “when to act?” question. After an empirical and theoretical analysis of AM and its context, in the second part of this thesis, I was interested on the real application of AM in the field. Therefore, I evaluated the capacity of forest actors to change their practices in a climate change context, with an original method based on the estimation of local capitals. Sadly, this analysis showed that for the moment, foresters implement more easily strategies for increasing robustness than resilient or transformative strategies, increasing the fragility of socio-ecosystems and risking a violent collapse of them.