Paleoclimatic relicts and climatic disjunctions in the Flora of Northern Portugal
Climate is generally considered the main factor determining the global distribution of plant and animal species.
Climate changes, depending on their rapidity and intensity, can give rise to events of (local, regionalor global) extinction, redistribution of flora and fauna, population genetic divergence, ecotype differentiation or even speciation. That is, climate changes reflect on both ecosystem structure and function, as well as on spatial organisation of the borders between biogeographic units, and eventually also on the genesis of both ecosystems and biogeographic units itsel.
Specific physical conditions working at a local scale (microclimate), such as rocky cliffs, watercourses or special types of rock, can enable the persistence of species in territories where the macroclimate is no longer appropriate for their occurrence. There are also those species whose taxonomic independence occurred under climate conditions which were very different from the current ones, and then became adapted to the plant communities developing under the new climate. If these species are common extant taxa elsewhere, they are called climatic disjunctions, but if their distribution is nowadays very restricted, they are known as climatic relicts.
A related concept is the one of "biogeographic relict". Traditionally, a biogeographic relict is anendemic taxon, with limited distribution range, descending of another taxon that was once widely distributed. Like many other concepts in Biogeography and Ecology, the concept of biogeographic relict depends on both space and time scales. Also, taxonomic entities of lower rank (the species and infra-specific ranks) are no more than useful abstractions, often very hard to relate to genetic distances. Therefore, we think it is possible to extend the concept of"relict" to the population level, at different biogeographic dimensions and time scales, as long as it is possible to relate current distribution patterns of those populations with specific palaeoclimatic periods and events. Within this wide concept of "relict", isolated populations of plants which are common in other biogeographic territories are here interpreted as climatic disjunctions. On the other hand, in order to keep the "taxon biogeographic relict" concept, we think it is more appropriate, on a small spatial scale, to speak of relict populations of a given taxon, or then, of territorial (local) relict, as long as thc specific biogeographic scale is referred.
Their specific survival conditions, the potential uniqueness of their genetic information, and the biogeographic significance of the plant communities they live in, give climatic relicts and disjunctians a remarkable conservation value. They are also precious sources of information concerning past climates.
ln this paper, we present a preliminary list of palaeoclimatic relicts and climatic disjunctions of the Northern Portugal flora. We recognise three main types of relicts occurring in the territory: I)Palaeoclimatic relicts (xerophytic and mesophytic subtypes); 2) Würmian temperate climatic disjunctions; and 3) Pre-würmian mediterranean climatic disjunctions. ln this first approach, we only listed those taxa whose isolated populations are clearly related to specific palaeoclimatic periods and events. For each taxon, we present information on ecology and distribution in Portugal. We also address the conservation status of these relict populations and discuss future perspectives for their long-term preservation in the territory.