Disparate response to water limitation for vessel area and secondary growth along Fagus sylvatica southwestern distribution range

Abstract

The response of European beech (Fagus sylvatica L.) to climate warming will depend on the ability of their populations to adjust tree performance to water shortage. By exploring inter- and intra-annual variations in secondary growth and mean vessel area (MVA), we assessed the effects of precipitation on cambial activity and hydraulic control during the vessel expansion phase along tree lifes. We sampled beech populations at low and high altitude from four mountain ranges across its southwestern distribution edge. We measured a total of 45,897 rings from 126 trees and 5.5 million vessels from 76 trees. We built chronologies for ring width and MVA between 1950 and 2017, calculated their climate responses and evaluated the effects of region, altitude and chronology type (ring-width vs. MVA) by means of ordinations (PCA) and constrained ordinations (pRDA). Precipitation controlled ring width and MVA along beech's southwestern distribution range, but at different time domains. Ring width responded primarily to summer precipitation during the previous growing season, whereas MVA responded to water availability during the vessel expansion phase, with timing shifting along the ring, according to the moment of vessel expansion. Regional differences were significant, but low, compared with the effect of chronology type. A large part of the variance explained by region was due to the strong difference between Western Pyrenees forests –growing under hyperhumid conditions– and the rest of forests under drier and warmer climate. Only minor differences between altitudes were found for the climate control of ring width and vessel size at annual scale, and no intra-annual effect on climate control of MVA. The stronger effect of chronology type on climatic response compared to the role of geographical location or altitude suggests common climate constraints on secondary growth and xylem anatomy along beech dry edge.