HISTORY, DISTRIBUTION AND ECOLOGICAL CHARACTERIZATION OF OLD GROWTH FORESTS IN SARDINIA

ABSTRACT - Thesis of Sergio Fantini: HISTORY, DISTRIBUTION AND ECOLOGICAL CHARACTERIZATION OF OLD GROWTH FORESTS IN SARDINIA. Old forests globally play a very important role. The most widely used definition of primary forest is: “Naturally regenerated forest of native species, where there are no clearly visible indications of human activities and the ecological processes are not significantly disturbed” (FAO). Their biodiversity, their ability to mitigate CO2 emissions, and to globally and locally modify the water cycle and climate, make these fundamental ecosystems very important to be studied and preserved. Globally, it is well known that currently primary forests are in decline. Also in Sardinia, only a small percentage of the original forest heritage was saved from the deforestation that began in the early nineteenth century and continued until after the half of the twentieth century. Despite the great importance, there was not a complete knowledge of the consistency, structure, distribution, threats and types of ancient forests. This research tried to fill, at least in part, these gaps and produced a first characterisation of the ancient residual forests of Sardinia. The first phase of the study consisted in the research, identification and field mapping of the oldgrowth stands. The feedback provided by local experts from public forestry agencies and research institutes universities through the compilation of a questionnaire was essential. A total of 68 plots were surveyed throughout the island. The identification of old-growth features was based on: amount of large-size and old trees, tree species composition, canopy heterogeneity, occurrence and amount of deadwood. The main goal of this work was to determine the degree of old-growthness of each single plot and, for this reason, several structural variables were surveyed. Because no one single proxy indicator can be a measure of old-growthness alone, a structural index (Structural Heterogeneity Index, SHI) was elaborated in order to summarisethe above-mentioned variables in one single value. Finally, how the SHI varied among environmental or human-related factors was statistically evaluated. In the second part of the work, the relationship between the presence of great longhorn beetles (saproxylic beetles that play an important role as an ecosystem engineer) and the structure of old-growth holm oak, the most widespread and representative forest type present in Sardinia, was analysed. Finally, the degree of protection of the old-growth stands from the legislative point of view and from wildfire hazard, was studied. These analyses, performed in GIS environment, allowed to identify which surfaces of the old-growth stands were included in the regional protection network and, through the visibility analysis of the fire lookouts network, the risk ofold-growth forest fires was assessed. To do this, the application of a parametric method allowed an assessment and the creation of a vulnerability map through the integration of visibility, old-growthness and wildfire hazard parameters of each oldgrowth stand.