Variations in the tree-ring structure of Norway spruce (Picea abies) under contrasting climates

Variations in tree-ring structure from pith to bark of mature Norway spruce (Picea abies Karst. (L)) grown under contrasting climate conditions (warm-dry vs. cool-humid) in south-western Germany were investigated. Sample trees were from even-aged stands where no intensive silvicultural treatments had taken place. The cell number (CN), diameter (CD), lumen diameter (CL) and wall thickness (CW) were measured from stem cross-sections taken at breast height. A raw data chronology of each cell parameter was established for the whole annual ring (AR), earlywood (EW), latewood (LW), and transition wood (TW). The long-term trends of the cell parameters were generally non-linear, parameter-specific in AR and EW and similar over sites. Those in LW were site-specific and similar over cell parameters. The variation of the same parameter, expressed by the coefficient of variance (CV), tended to increase from EW towards LW and was clearly higher for CN than for other cell parameters of all tree-ring zones. Trees from the warm-dry site had more LW cells and substantially thicker CW, whereas those from the cool-humid site had larger EW cells. These observed differences are likely due to the hydraulic adaptation mechanisms of trees to different site conditions.