Within-tree variations in shoot differentiation patterns of 10 tall tree species in a Japanese cool-temperate forest

Abstract

The relations of leaf–stem balance, stem thickness, leaf thickness, and leaf size to stem length of current-year shoots were compared between terminal and lateral shoots in saplings of 10 tall tree species in a Japanese cool-temperate forest. Six monopodial and four substitution sympodial branching species were studied. For both terminal and lateral shoots, the ratios of leaf area / stem length, leaf mass / stem mass, and leaf number / stem length were greater in shorter current-year shoots, implying shoot differentiation such that short current-year shoots specialize in leaf display and long current-year shoots in crown expansion. These ratios were generally greater for terminal shoots than for lateral shoots, especially in the lower range of stem length. This tendency was more conspicuous in the ratio leaf area / stem length than in leaf mass / stem mass and leaf number / stem length, because terminal shoots showed greater stem mass / stem length, leaf area / leaf mass, and leaf area / leaf number ratios than lateral shoots. These terminal–lateral variations were generally greater in the monopodial species than in sympodial species. These observations are discussed in relation to differences in ecological functions and hydraulic architecture between terminal and lateral shoots, and in relation to apical control and branching patterns (the monopodium and the sympodium).Key words: shoot functions, apical control, short shoots, terminal shoots, monopodial branching, substitution sympodial branching.