Dynamics of P. pinea and P. pinaster forests: Implications for adaptive management in a climate change context

Abstract

Over the last decades, climate change has been particularly severe in the Mediterranean basin, where the intensity and frequency of drought events had a significant effect on forest dynamics. As a consequence, tree allometry is modified, reducing tree and stand growth, provoking tree or stand decay and dieback and altering plant recruitment. In this context, differences in structural and physiological strategies of tree species, could mitigate the damage inflicted by climate change and reduce risk. Programs aiming to adapt forests to climate-changing conditions should take profit from the knowledge of these strategies, and propose a set of actions oriented to emulate or enhance the inherent capacity of the forest for adaptation. Between these actions, this thesis highlights the promotion of natural regeneration or the increase of intra and interspecific diversity. A most diverse ecosystem could help to reduce vulnerability and increase resistance against the lack of water availability. In addition, tree species interactions could lead to complementary effects during low-growth years by the optimization of resources. This thesis provides a variety of methodologies based on analyzing how different factors control the response dynamics of P. pinea and P. pinaster in mixed and monospecific Mediterranean forests throughout stand development, from regeneration to adult stages. The main hypothesis was that species responses, could help to cope with climatic variability and that the composition, mixed or monospecificic, could attenuate these responses. The thesis used data from a network of 1936 plots of 0.02 ha to study natural regeneration, and a network of 75 mixed and monospecific temporal plots on adult stands, both installed in the Northern Plateau of Spain. In this last group of plots, the use of tree-ring width series permitted us to evaluate species-mixing effects on inter-annual and intra-annual tree growth dynamics.