Conservation of a threatened marginal population of Cistus albidus of Lake Garda (Italy)

The population of Cistus albidus of Lake Garda (N-Italy), present at the northernmost margin of its range, is endangered by urban development and extreme climate events. Since this species has been continuously declining for over 200 years, conservation actions are necessary to prevent its extinction. To identify the best sites for an assisted colonisation of the species in the area, we carried out experiments posing 120 plantlets grown from seeds from the natural population in each of 5 sites within a 20 km range from the natural population. Environmental, demographic and meteorological parameters were monitored for 8 years at each site to evaluate the response to our intervention. Demographic changes occurred at different rates, reflecting the effect of environmental factors on new plants establishment and survival; the final survival rate of reintroduced plants was 45.3%. Unlike winter temperature, summer drought had a strong negative impact on plant survival. Inter-population comparison suggests a formerly wider distribution of the species, and bodes well for the survival of the newly created populations. Differentiating between ecological factors influencing growth and those regulating reproductive biology and success of new generations will help to improve long-term fitness and viability in assisted colonisation projects.