Dendroclimatic responses of four European broadleaved tree species near their southwestern range edges

Iberian temperate forests are distributed along the boundary between the Atlantic and the Mediterranean biogeographical regions, and represent the south-western range edges of diverse European broadleaved deciduous tree species. Trees growing at the boundary between Atlantic and Mediterranean biomes suffer from different stresses, including increasing moisture deficit which has been identified as one of the main limitations for growth. In this work, dendrochronological techniques were employed to characterize the radial growth of Acer campestre L., Fagus sylvatica L., Fraxinus excelsior L., and Quercus robur L. in a mixed forest in northern Spain, and examine its relationships with local climate near their south-western range edges. Acer and Fagus tree-ring chronologies showed the highest common signal and the strongest responses to climate. Positive effects of precipitation, especially in the previous December and current summer, were relevant for growth of all species. Only Acer growth showed a detrimental effect of maximum diurnal temperatures in the previous autumn and current summer, while Fraxinus and Quercus growth was benefited by above-average winter temperatures. Cloud cover strongly improved the radial growth of all species, probably because cloudy conditions mitigate the detrimental effects of summer water depletion and low winter temperatures. The beneficial effects of precipitation and cloudiness on tree growth were temporally unstable and have become significant generally since the 1970s, suggesting that rising temperatures and decreasing rainfall shape radial growth-climate relationships of broadleaved deciduous trees near their southern range edges