Response patterns of xylem and leaf phenology to temperature at the southwestern distribution boundary of Quercus robur: A multi-spatial study

Abstract

We investigated how temperature patterns affect cambial activity and leaf phenology of oak across a wide range of natural woodlands at its southwestern distribution boundary. Understanding the climatic control of wood formation in dominant species is very relevant to infer tree responses to ongoing environmental changes and their impact on the carbon cycle. We selected nine sites along two elevation gradients from the coastline in northwestern Iberia, and sampled ten trees per site biweekly during 2012 and 2013. Leaf and cambial phenological phases were related to mean air temperature for 10–60 day running periods along the year to identify the most relevant time windows for cambium and leaf phenophases, and the relationships among them. The first earlywood vessels expanded before the appearance of small leaves, and subsequently underwent maturation to meet water requirements for full leaf unfolding. The advance or delay of cambial reactivation and budburst varied among sites and years modulated by spring temperature, and were respectively maximized by maximum and minimum values. Temperature can modify the onset of early phenophases of primary and secondary growth differently, and also the synchronicity between them. However, the maturation of the first earlywood vessels is necessary to undergo full leaf extension.