Effects of six years snowpack manipulation on growth and phenology of common juniper (Juniperus communis L.) at high elevation

Climate change is nowadays a well-known and global phenomenon with multiple effects: from the warming trend in lands and oceans, to the biodiversity and ecosystems loss, from the ice sheets shrinking, to the increase in the intensity and severity of extreme events. Among all, an issue resulting from those changing climatic conditions is the decrease of the amount and number of snow precipitation events during the snow season that, together with increased temperature, is inducing a reduction of snow cover permanence in mountain areas. This affects the distribution, growth and phenology of many plant species that live in those areas and are directly or indirectly dependent on snow cover dynamics thanks to complex evolutionary processes. It is, therefore, useful to collect as much information as possible about the new snow cover dynamics and shrinking permanence to better understand how plants will respond and how the composition of mountainous vegetation will change in the future if the current tendency will continue. This study will focus on common juniper (Juniperus communis L.), which is the conifer with the widest distributional range in the northern hemisphere, and its responses to different levels of snow cover. The aim is to assess the effects of snowpack duration on the phenology and growth of this species. A six-years snow manipulation experiment was carried out in an experimental plot above the treeline on previously selected plants which were subjected to altered snowpack duration (C: prolonged, S: reduced, N: natural) to simulate different snow cover lengths. During the growing seasons we collected data on phenological traits (buds’ development, shoot growth). The results show that a prolonged snowpack duration had an effect in the initial growth period, in which the growth rate was slower than the other treatments, probably because of a detrimental effect that persisting snow could have on growth. A reduced snowpack duration, on the other hand, caused a higher growth in the first years because of a longer exposure to solar radiation for the photosynthesis, but, in the following years, this effect faded out. The convergence in the growth in all the treatments that we observed in the recent years could represent an acclimatation mechanism.