Sympodial and monopodial branching in Acer: implications for tree architecture and adaptive significance

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Abstract
To understand the adaptive significance of sympodial and monopodial branching in Japanese Acer, growth patterns of vigorous saplings and their consequences for tree architecture were examined in 6 sympodial species (exhibiting sympodial branching) and 14 monopodial species (exhibiting monopodial branching). All sympodial species were characterized by weak dominance of a main lateral branch and its large branching angle with the leader branch it developed (referred to as the SS type). The monopodial species were divided into two types. One, the ME type, was characterized by strong dominance and a small branching angle of a terminal branch, and the other, the MS type, by intermediate dominance and a small branching angle. The computer simulations showed that the growth pattern of the SS type would result in a vigorous sapling with many horizontally spread branches, that of the ME type with a large amount of vertical growth, and that of the MS type with an intermediate architecture between these two types. The SS, MS, and ME types were recognized as strategies adapted to less sunny, intermediate, and more sunny sites, respectively.