Shoot elongation, leaf demography and bud formation in relation to branch position on Larix laricina saplings

Abstract

Shoot development was investigated on branches of Larix laricina (Du Roi) K. Koch trees growing in their 8th year in two plantations and in a natural stand approximately 12 years old. Expansion of throughout-crown series of short and long shoots was measured weekly, and later colour change and natural fall of leaves were assessed. Similar shoots were collected at intervals and dissected, the long shoots by 25-leaf segments. Leaf area and weight, as well as time of bud formation, were determined. Increasing acropetal trends were evident in time to bud burst: duration of short-shoot leaf-cluster expansion; size of leaf clusters and number, area and weight of leaves per cluster; duration and rate of long-shoot elongation; number, area and weight of leaves on long shoots; time to terminal-bud formation on long shoots. Along each long shoot, stem and leaf elongation and lateral-axis formation progressed acropetally. Lateral axes were most numerous on second to fourth 25-leaf segments. On longer shoots, some axes in middle segments developed as sylleptic short shoots rather than as lateral buds. Leaves of short shoots and basal leaves on long shoots turned yellow and abscissed sooner than axial leaves on long shoots. Colour change and loss among axial leaves were acropetal along shoots and up the crown. Thus, last-formed leaves, in axils of some of which lastformed lateral buds occurred, were held longest.