Relation between the permeability and the anatomy of jack pine sapwood with stand development

The anatomical characteristics of sapwood from the base of the live crown of trees from 11 jack pine stands (Pinusbanksiana Lamb.) of different age and site quality were related to the patterns of change of longitudinal sapwood permeability (k) previously observed to occur among these stands. Tracheid length (L t ) increased rapidly from a minimum of 1.9 mm to a plateau of around 3.6 mm as stand age and site quality (productivity class) increased. Sapwood relative water content (R s ) measured before saturation ranged from 78 to 85% for the majority of trees. Samples taken from trees growing on poor sites, however, exhibited significantly lower values of R s , which probably resulted in their remaining below saturation during the determination of sapwood permeability. The lower R s values were assumed to be reflective of more adverse water balances during the growing season associated with rapidly drained and (or) shallow soils. Tracheid lumen diameter (D l ) was positively correlated with k within age-classes 15 and 35, but not thereafter. The initial relation between D l , and k is thought to be associated with corresponding increases in the area of pit membranes, which determines the number of pores within a pit membrane. Values of k were never more than 60% of the values calculated by Poiseuille's law for ideal capillaries (k c ) and were generally less than 40%. Values of k tended to approach k c with increasing L t and decreasing D l . Overall, Poiseuille's law by itself could not explain the changes in the hydraulic properties of jack pine sapwood with stand development. However, L t and R s could together account for 72% of the variation in k. Young stands that had different k depending on site quality generally had corresponding differences in L t , R s , and (or) D l . Mature stands that had reached maximum k on all quality sites no longer showed differences in L t , R s , or D l .