Abstract
Relic laurophyllous plant species belong to lineages that evolved within the Tertiary laurel forest during a climate phase that was warmer and more humid than nowadays. These plants survived the Quaternary climate deterioration, which led to the extinction of almost all Tertiary flora. Some studies have inferred or reported a northern shift of their ranges due to current climate change. Furthermore, even land-use changes are affecting the pattern of laurophylls distribution. Given the biogeographical importance of relic laurophylls, ecological studies on this topic are of fundamental importance for defining proper management and conservation actions. This study analysed the ecology of relic laurophylls at the level of communities, species and populations within the reference system of the Italian flora. A national vegetation-plots database, presented in chapter I, was the main tool utilized to approach the study aims. In chapter II, from among the Italian flora, we selected relic laurophylls occurring in a climatic niche similar to the present-day laurel forests of the Eurasian continent. This set of species was used to localize potential refugia and to identify habitat suitability. Chapter III presents the coenological amplitude and the ecological niche of one of the most emblematic relic laurophylls, i.e., Laurus nobilis L. (Laurel). The results were discussed to give consistency to conservation practices of the European Habitat Directive. Chapter IV describes the population structure of laurel in 16 forests of central Italy and the effect of browsing and rooting on its regeneration process. The analytical potential and usefulness of a vegetation-plot database is shown in the first chapter of the thesis. Chapter II discusses and demonstrates how few relic laurophylls occupy a climatic niche comparable to present-day laurel forests in terms of precipitation, although not necessarily in terms of temperature. Refugia areas for these species are mainly located on the mountain ranges of central Italy, underlining the historical importance of temperate sites during the Quaternary climate deterioration. Generally, most Italian forests are suitable for relic laurophylls. This fact highlights that limited postglacial range recolonizations provide a better explanation of the distribution pattern of laurophylls than current climate. The data presented in chapter III shows how laurel has a wider coenological amplitude in respect to other relic laurophylls. In fact, it occurs in warm and humid sites, as well as hot and dry sites with nutrient and moisture in the soil. Furthermore, there are discrepancies between the results in this study and guidelines of the European Habitat Directive. In Chapter IV, the revealed population structures of laurel suggest a potential increase of species occurrence within the forests of central Italy. However, there is a negative impact on laurel juveniles induced by browsing and rooting within nature reserves. Lastly, a discussion is offered regarding the implications for management and conservation of relic laurophylls.