drought stress, gas-exchange, iWUE, C:N ratio, root collar diameter
dendrochronology, palaeoclimatology, proxy archives, stable isotopes, tree rings
Altitudinal gradient, Climate change, chronologies, plant water use efficiency, Quercus spp., tree-ring carbon isotopes
δ13C and δ18O, analytical comparison, isotope chronologies, isotope ratio mass spectrometry, paleoclimate proxies, tree-ring stable isotopes