Oaks are keystone species in European temperate forests. Nemoral oaks (Quercus robur, Q. petraea) are widespread all throughout the continent, but reach their southern distribution boundary in northern Iberia. In the Mediterranean Region, they are replaced by evergreen oaks, but ‘sub-Mediterranean oaks’, i.e., drought-resistant deciduous oaks with marcescent leaf habit usually occur at the transition areas. But according to prediction models, climate change is expected to modify the future distribution areas of these species.
The northwestern Iberia Peninsula is one of the coexisting areas of oaks at their distribution boundaries. In fact, Q. robur is progressively replaced by the sub-Mediterranean Q. pyrenaica, as summer drought increases. However, ‘classical’ tree-ring analyses often fail at identifying the main climate-growth relationships probably due to the lack of a single prevailing limiting factor.
In this talk, I will show the analyses we have been carrying out for the last years at the Department of Botany of the University of Santiago de Compostela (Spain). In order to understand the main climatic factors affecting growth performance of oak, we apply dendrochronological techniques to the characteristics of earlywood vessels (quantitative wood anatomy), and study the dynamics of cambial activity (xylogenesis) for the interpretation of the climatic relations found. The combinations of these techniques with ring-width analysis are capable of providing a much more complete overview on the behavior of oaks along their distribution boundary.