Cold temperature extremes during spring do not limit the range shift of Mediterranean pines into regions with intermittent frost

Bioclimatic envelope models have predicted latitudinal range shifts of tree species in Europe following climate change. Accordingly, Mediterranean species will be able to migrate northwards if climatic conditions become warmer and dryer. Frost, on the other hand, is an important and recurring factor in temperate and boreal regions causing damage to buds and leaves, and potentially limiting the survival of Mediterranean tree species or populations at higher latitudes. Since species distribution models rely on average climatic parameters, they may underestimate the risk of frost damage from low temperature extremes. We measured the cold hardiness of Pinus sylvestris, Pinus nigra and Pinus halepensis seedlings from a total of 11 European populations growing in a common garden in a cold Central Alpine valley on seven dates between February and July 2013. On each date, needles were artificially frozen at several temperatures and the temperature estimated at which 50% of the needle tissue is ...