Análisis de la dinámica de los robledales (Quercus pyrenaica Willd.) frente al cambio global en el límite sur de su distribución (Sierra Nevada)

Résumé

The study of the ecological dynamics of populations located at the limits of their distribution is considered essential to establish appropriate management guidelines under current climatic uncertainties. Rear-edge populations are usually adapted to local environmental conditions at the limit of the ecological range of the species, and often show long-term persistence. Local responses to environmental changes may differ from the average response of the species, and such differences may promote or hinder the survival of the rear-edge populations under current conditions of global change. Q. pyrenaica populations of Sierra Nevada represent one of the southernmost margins of this species’ range. They are located in a mountain region that has served as a refuge for the species. Like other Mediterranean forest formations, Q. pyrenaica woodlands have been subjected to intense anthropogenic pressures over time, which has led to a reduction in their extent and a modification of their floristic composition and structural patterns. Historically, Q. pyrenaica forests been exploited in coppices for firewood, charcoal and tannins. They were also cleared to generate large grazing areas. All these actions led to an overexploitation of the Q. pyrenaica woodlands, so that the current configuration of these formations in the Sierra Nevada seems to depend largely on past use. However, from the second half of the 20th century onwards, traditional activities were abandoned, resulting in a decrease in anthropic pressure on forest ecosystems. Paradoxically, many Q. pyrenaica forests present an advanced state of degradation (regeneration problems, high tree stand densities, growth stagnation, among others). These problems may be aggravated in the current context of climate change, especially considering the high vulnerability of Q. pyrenaica to climate change, and particularly for populations located at the rear edge of its distribution range such as Sierra Nevada. Therefore, understanding the ecology of populations located at the rear edge of its distribution is key to evaluate the response of the species to changing environmental conditions. The general objective of this doctoral thesis is to analyze the functioning dynamics in the face of global change of Q. pyrenaica populations located in Sierra Nevada, a mountainous region that represents one of the geographical limits of its distribution, where these formations have been subject to intense anthropic pressures.