CROWN DEVELOPMENT OF COASTALPSEUDOTSUGA MENZIESII, INCLUDING A CONCEPTUAL MODEL FOR TALL CONIFERS

Abstract

Seventy trees from seven stands 50–650 years old were selected for this investigation of crown structural development inPseudotsuga menziesii. All branches, limbs, and trunks were nondestructively measured for size, structure, and location while climbing the trees with ropes. These data were used to generate a computer model of each tree's crown that was error‐checked trigonometrically. Leaves, bark, cambium, and wood were quantified by using limited destructive sampling to develop predictive equations that were applied to the complete inventory of structures in each tree's crown. Summations of these values yielded whole‐tree estimates of several structural variables. A second set of equations was then developed to predict these whole‐tree parameters from simple, ground‐based measurements. Principal components analysis of 24 tree‐level variables revealed two orthogonal dimensions of structure that accounted for 71.3% and 12.4% of total variation in the 70 trees. The first dimension represented a gradient of overall tree size and structural complexity that was positively correlated with tree age (R2= 0.89). The second dimension represented a gradient of incremental growth potential that was positively correlated with measured growth of main trunks at breast height during the five‐year period after trees were mapped (R2= 0.39). The strongest determinant of incremental growth potential was the ratio of a tree's total cambium surface area to projected leaf area. A tree's incremental growth potential may thus be unrelated to either size or structural complexity and depend instead on factors related to whole‐tree carbon balance (e.g., how much the tree invests in fighting and feeding fungi). Our intensive analyses ofPseudotsuga menziesiiand extensive observations of other species were used to develop a conceptual model of crown development in tall conifers. Trees respond to disturbances by growth of replacement structures whose form depends on disturbance intensity and age. Young trees rebuild damaged crowns through epicormic shoot production on original branches, whereas older trees also recover by producing new, epicormic branches. Damage to main trunks and top dieback stimulate production of reiterated trunks. Repeated damage leads to multiple hierarchical levels of trunk reiteration as well as to limb formation and increasing tree individuality.