Evidencias pasadas y proyecciones futuras de cambios climáticos y ecológicos en bosques de la cuenca mediterránea y la cordillera del Himalaya.

Abstract

GENERAL ABSTRACT Modifications in climatic conditions have been observed globally with increases in temperatures and modifications in rainfall patterns and distribution. This situation has given rise to processes of growth limitation, decline and mortality in forest ecosystems in a multitude of ecosystems. These processes do not affect all regions in the same way. The Mediterranean basin, due to its seasonal climate with regular periods of drought, which are expected to increase both in intensity and frequency, is a region that is particularly sensitive and vulnerable to climate change. This situation is also particularly severe in the Himalaya region, which is undergoing more accelerated climatic changes than the rest of the regions worldwide. This, together with the great diversity of this region and its particular climate modulated by the monsoons, makes it a particularly sensitive and vulnerable region in the face of climate change. It is therefore essential to understand the functioning and responses of forest ecosystems in order to predict their behavior and carry out effective forest management measures to reduce their vulnerability and increase their capacity to respond to extreme climate events. The role that conifers play in mountain forest ecosystems is remarkable, and among all conifers, it is worth mentioning the unique role of A. pinsapo, a relict species located in the Sierra de las Nieves Natural Park with a fragmented spatial distribution, with processes of decay and mortality and population isolation. In order to understand how the growth of this species is modulated by climatic conditions, we have carried out different multidisciplinary studies throughout this Doctoral Thesis. In these studies, analyses have been carried out to verify how the growth values (Ring Width, Ring Width index, Early Wood, Late Wood), intrinsic age values of each individual together with the elevation of these values can modulate the climatic sensitivity of A. pinsapo. In addition, local climatic variables (precipitation and temperature) and regional and global atmospheric patterns (Westerly Index and North Atlantic Oscillation) were studied, as well as the genetic diversity of different study sites (nSSR;nuclear simple sequence repeats, cpSSR; chloroplast simple sequence repeats) and the modulation that these exert on the growth of individuals. More broadly, Linear Mixed Models (LMM) have been performed in the Himalaya region in order to carry out reconstructions and growth predictions for a multitude of species under different climate change scenarios (RCP 26-45-60-80 models obtained from CIMP5) in the Himalaya region. This allows us to evaluate and detect species that are especially vulnerable and will see significant reductions in their annual growth rates in order to be able to carry out forest management techniques to reduce their vulnerability. It is noteworthy that during the development of all the research a total of 23 species have been studied in the Mediterranean basin and the Himalaya region, thus covering a wide variety of response to climate and climate change along with a wide spatial range. There are several studies on the decline and mortality in conifer ecosystems from a climatic point of view. There are also studies on the impact that different forest management techniques, such as thinning, have on ecosystem structure and dynamics. However, these studies tend to study the short-term effect of these techniques. That is why in this thesis we study the impact of forest management techniques such as thinning and the effect they have in reducing the vulnerability of A. pinsapo individuals associated with reduced competition and better utilization of resources. However, our thesis proposes an innovative approach in this aspect, carrying out a long-term study of the benefits associated with these techniques and how they vary over time. It is noteworthy how variables such as Resistance, Resilience, Recovery and Relative Resilience are studied pre and post thinning treatment, with the aim of identifying lasting and significant changes. In general, our results show disparate behaviors among the different species studied in the Himalaya region with some of them seeing a very important increase in their growth values, while others show mortality of individuals. Likewise, we can observe how A. pinsapo is a very drought-sensitive species that is expected to present very important growth limitation processes during the next years if forest management measures are not carried out. However, these forest management measures show how they are effective in the short term, but their effects diminish in the long term.