Optimisation of forest management under climate change in the French maritime pine (Pinus pinaster Aiton) forests

Key message: A modern portfolio optimisation was performed on simulation data to optimise management alternatives of maritime pine (Pinus pinaster Aiton), under climate change. The objective was to maximise the biological productivity while minimising the inter-annual variability, until 2100, taking into account local variations in precipitation and soil available water capacity. We show that combining pine management alternatives helps to stabilise forest productivity. Optimal management portfolios must be flexible and reevaluated periodically to be adjusted to a changing climate. Context: The adaptation of forest management to climate change is poorly documented on a local scale, taking into account both soil and climate heterogeneities of the forest. Our study focuses on the management of planted maritime pine (Pinus pinaster Aiton) in South-West France. Aims: This paper presents a novel analytical framework to identify strategies maximising maritime pine forest productivity while ensuring its temporal stability under future climate at sub-regional scale, i.e. within the 1 Mha vast Landes de Gascogne forest. Methods: We used the mean-variance optimisation method to identify the optimal management portfolios for the Landes de Gascogne forest. The process-based model GO+ was used to simulate the forest annual production from 2006 to 2100 for four management alternatives under two climate change scenarios (RCP 4.5 and 8.5), two rainfall patterns and three levels of available soil water capacity. Subsequently, productivity mean and temporal variance were calculated over a 30-year sliding window spanning the twenty-first century. The distribution of management alternatives across the forest was optimised in order to achieve the desired balance between high mean and low variance for productivity. Management alternatives considered are variations of the classic management of this production forest, changing by the length of rotation and density. One is a prospective alternative, with thinning to reduce water deficit. Results: Under the RCP 8.5 climate projection, mean productivity was projected to decline over the course of the century, while inter-annual instability was expected to increase. In contrast, RCP 4.5 predicted a tipping point in mean productivity in 2040, followed by a decline. At the forest level, the optimised portfolios combined between one and four management alternatives depending on climate and risk aversion of the forest managers. In addition, the optimal portfolios were dynamic in nature and changed over time with future climate predictions. Conclusions: A combination of management alternatives was necessary to ensure a stable productivity in face of anticipated climate change. Furthermore, the optimal portfolio should be flexible and re-evaluated periodically when a stand is about to be regenerated (plantation or natural regeneration). Our findings highlighted the importance of the management alternative regulating tree density in response to water deficits as a key element in risk-averse strategies.

Duke Scholars

Author Jean Christophe Domec Environmental Natural Science