Warming-related growth responses at the southern limit distribution of mountain pine (Pinus mugo Turra ssp. mugo)

Questions: Could mountain pine (Pinus mugo Turra spp. mugo) located above the timberline and at the edge of its potential geographical distribution be a promising species to monitor climatic change in peculiar environments, such as the Mediterranean mountains? Does mountain pine krummholz upward expansion result from the current climate change? Have the relationship between climate and tree-ring growth of mountain pine changed? And, and to what extent does a climatic variability affects tree-ring growth? Could mountain pine upward expansion contribute to the loss of biodiversity in the undisturbed treeline ecotone on the Majella massif? Location: Majella National Park, Apennines (Italy). Methods: Dendroclimatological analysis was performed to examine the relationship between tree rings of mountain pine and climatic parameters at the tree line. Climate-growth relationships were analysed by correlation function (CF) analysis and moving CF (MCF). Results: In the Majella massif, climate variables affected mountain pine tree growth at the treeline ecotone. Significant correlations were found with the spring maximum temperatures and summer precipitation. Essentially, three months played a key role in mountain pine growth: April, May and October of the previous year. MCF showed that mountain pine is a sensitive species, in terms of tree ring growth. Conclusions: Growing above the limit of tree vegetation, mountain pine proved to be a promising species for monitoring climate- and land use-driven influences over tree ring growth at high elevation. Our results showed that mountain pine is very sensitive to climate, particularly at the beginning and at the end of the growing season.