Crown structure differences and dynamics in 100-year-old and old-growth Eucalyptus obliqua trees

Summary The crown structures of eight old-growth (∼450 y) and eight 100-y-old intermixed Eucalyptus obliqua trees at Warra LTER, southern Tasmania, were mapped by direct climbing and vector-based surveys. The quantitative maps were statistically compared between age classes. The older trees had a more variable crown structure and size range when compared with the unaltered growth pattern of branches in the generally rounder-crowned younger trees. The older trees were more decayed, with more dead wood in the crown and, in some cases, a snapped trunk. The 100-y trees averaged 44.5 m tall, 1.04 m DBH and 14.1 m3 trunk wood volume. The older trees were larger in many dimensions, averaging 60.8 m tall, 2.79 m DBH and 97.3 m3 trunk wood volume. Principal components analysis delineated the age classes clearly along Axis 1, weighted on measures of tree size and branch size, and slightly less so along Axis 2, weighted on branch numbers and total crown volume. Evidence of higher structural diversity was detected in old trees lacking visible evidence of fire and in 100-y trees that were less dominant in the canopy. Marked differences in crown structure were detected visually, and the inter-branch dynamics at the tree scale responsible for these differences elucidated an analogy to inter-tree dynamics at the forest scale.