DOI: 10.5061/dryad.5r0f0
title: Data from: Cold temperature extremes during spring do not limit the range shift of Mediterranean pines into regions with intermittent frost

description: 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 damaged (LT50; relative electrolyte leakage). Cold
 hardiness did not differ between populations of the same species and was
 not related to the minimum temperatures at the seed origin. In comparison
 with deciduous trees, Mediterranean P. sylvestris and P. nigra maintained
 extremely wide safety margins against frost throughout late winter and
 spring. By contrast, safety margins of P. halepensis were much narrower
 until March and winter cold hardiness was in the range of regularly
 recurring low temperature events in Central Europe. According to the
 measured LT50 values, the migration of a wide range of drought-tolerant
 populations of P. sylvestris and P. nigra from the Mediterranean to
 Central and Western Europe is not limited by intermittent cold temperature
 extremes in spring. They are notably as well adapted to frost as
 populations from Central Alpine origin. Differences in dehardening
 patterns between species demonstrate the importance of analysing cold
 hardiness repeatedly during potentially sensitive periods in order to
 predict species range shifts in the context of climatic change.
description: Relative electrolyte
 leakage of frost-damaged Pine needlesPines needles of
 seedlings from a common garden experiment have been artificially subjected
 to different levels of frost stress. They were subsequently incubated in
 deionized water and conductivity of the solution was measured. The samples
 were then autoclaved at 121ºC and conductivity was measured a second time.
 The two conductivity measurements are used to calculate the 'relative
 electrolyte leakage' (REL) of damaged needles, an index of injury for
 frost damage.Conductivity.csvValues of LT50 of frost-damaged pine needlesLT50 of frost-damage was calculated based on the relative electrolyte leakage (REL) of pine needles, derived from conductivity measurements from a common garden experiment. The LT50 was calculated with a non-linear regression using the freezing temperature as independent variable.LT50Values.csv