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?