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

Questions: Could mountain pine (Pinus mugo Turra subsp. mugo) located abovethe timberline and at the southern limit of its potential geographic distributionbe a promising species to monitor climatic change in specific environments suchas the Mediterranean mountains? Does mountain pine krummholz upwardexpansion result from current climate change? Has the relationship betweenclimate and tree ring growth of mountain pine changed? To what extent doesclimatic variability affect tree ring growth? Could mountain pine upwardexpansion contribute to loss of biodiversity in the undisturbed tree line ecotoneon theMajella massif?Location: Majella National Park, Apennines, Italy.Methods: Dendroclimatological analysis was performed to examine the relationshipbetween tree rings ofmountain pine and climatic parameters at the treeline. Climate–growth relationships were analysed using correlation function(CF) analysis andmoving CF (MCF).Results: In the Majella massif, climate variables affected mountain pine treegrowth at the tree line ecotone. Significant correlations were found with springtemperatures and summer precipitation. Essentially, three months played a keyrole in mountain pine growth: April andMay of the current year and October ofthe previous year. MCF showed that mountain pine is a sensitive species, interms of tree ring growth.Conclusions: Growing above the limit of tree vegetation, mountain pineproved to be a promising species for monitoring climate- and land use-driveninfluences over tree ring growth at high elevations. Our results show thatmountain pine is particularly sensitive to climate at the beginning and at theend of the growing season.