RELATIONSHIPS BETWEEN SAPWOOD AMOUNT, LATEWOOD PERCENTAGE, MOISTURE-CONTENT AND CROWN VITALITY OF DOUGLAS-FIR, PSEUDOTSUGA-MENZIESII

Relationships between sapwood amount, latewood percentage, moisture content and crown vitality were studied in 171 Douglas firs [Pseudotsuga menziesii (Mirb.) France] belonging to different vitality classes. The trees originated from 10 stands in the Netherlands varying in age from 25-70 years. Both age and vitality have a significant influence on the absolute and relative amount of sapwood. Predictably, older trees have a lower relative amount of sapwood than young trees. Non vital trees show a lower amount of sapwood both absolute and relative, although overlap with more healthy trees exists. Non vital trees show a lower average latewood percentage in the sapwood, but here also there is overlap with more healthy trees. The latewood percentage in the last formed five annual rings of non vital trees is even lower. It is hypothesised that the hydraulic 'fitness' of the sapwood in non vital trees remains unaffected because the lower amount of sapwood in those trees coincides with a higher earlywood percentage, which allows for greater conductivity. In ten trees the moisture content in each growth ring at four height levels in the trunk was measured. The moisture content in the sapwood rings at breast height is significantly lower than in and just under the crown. The moisture content of the heartwood rings at all height levels is about 30-35%, which is very close to the fibre saturation point. The moisture content in sapwood growth rings is significantly and negatively correlated with the latewood percentage. The sapwood was completely water saturated in one tree only; in the other trees the moisture content was about 80-90% of the calculated maximum value. Because of the very limited range of vitality classes in the trees studied no indication could be given whether crown vitality influences sapwood moisture content. The levels found in this study are indicative of hydraulic fitness of all trees. A higher moisture content coincided with a lower relative sapwood area and also with a lower latewood percentage. In the overall sample this relationship between latewood percentage and relative sapwood area was only also found for trees in the age class of c. 50 years old. It was not valid for the younger and older trees.