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

Questions Could mountain pine (Pinus mugo Turra subsp. mugo) located above the timberline and at the southern limit of its potential geographic distribution be a promising species to monitor climatic change in specific environments such as the Mediterranean mountains? Does mountain pine krummholz upward expansion result from current climate change? Has the relationship between climate and tree ring growth of mountain pine changed? To what extent does climatic variability affect tree ring growth? Could mountain pine upward expansion contribute to loss of biodiversity in the undisturbed tree line 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 using correlation function (CF) analysis and moving CF (MCF). Results In the Majella massif, climate variables affected mountain pine tree growth at the tree line ecotone. Significant correlations were found with spring temperatures and summer precipitation. Essentially, three months played a key role in mountain pine growth: April and May of the current year 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 elevations. Our results show that mountain pine is particularly sensitive to climate at the beginning and at the end of the growing season.