Phenological and genetic characterization of Mediterranean plants at the peripheral range: the case of Cistus albidus near Lake Garda

The potential effects of climate change on the distribution of Mediterranean plants at their peripheral range make them extremely vulnerable to environmental fluctuations. The northern-most Italian population of Cistus albidus provides an outstanding case for study, as it grows at the extreme northern edge of its range and because phenological data have been available since the early XIX century. In the period 2012–2017, we analysed the population demography and spatial structure, growth and flowering phenology, and genetic variability to understand the history, current state and possible evolution of this population. Lastly, the population data were tested for association with environmental factors. The population studied consists of plants on average 10 years old, showing the highest growth rates in spring and autumn. Anthesis starts in April and ends in early June and is significantly dependent on temperature. High levels of genetic variability are present (average He = 0.471), with heterozygote excess detected at four loci out of five. Bayesian analysis does not support any genetic structuring of the population. The aggregated pattern in the distribution of individuals and their phenological traits, together with the absence of genetic structuring, seem to suggest that this extreme geographical population is not currently endangered.