Tree-ring Growth and Structure of Pinus uncinata and Pinus sylvestris in the Central Spanish Pyrenees

Abstract

We compared tree-ring structure and formation for Pinus uncinata Ram. and Pinus sylvestris L. in the Central Spanish Pyrenees. Ring width and the number of tracheids in the latewood and in the entire ring were measured monthly during the growing period in 1993. Both species developed the major part of the tree ring between 10 June and 18 July, although the tree ring formed earlier in P. sylvestris. Tree-ring growth was delayed in the highest elevation stand. Ring width and the number of tracheids in the tree ring were functionally correlated. Pinus uncinata had smaller tree rings with fewer cells in radial transects. Latewood development, including formation, later coloration, and cell wall apposition, started in July and ended in October. Tree rings show greater latewood density and color contrast in P. uncinata. Characteristic tree rings show latewood tracheids with thin cell walls and wide cell lumina in many P. sylvestris cores. The analysis of the intra-annual ring growth and structure variability has thrown light on some interannual assumptions such as phenological variability controlled by climate. In conjunction with past dendroclimatological studies, this work shows the existence of a delay between ring growth and structure and their controlling climatic factors.