Stem orientation is related to growth rate, leaf dimensions, and the deciduous habit in temperate forest saplings

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The orientation of the central stem is a key component of tree architecture. Stem orientation was related to extension rate in saplings growing in light conditions ranging from forest understories to large openings in 11 deciduous angiosperms, 1 evergreen angiosperm, and 2 evergreen conifers in the Appalachian Mountains of the southeastern United States. Most of the deciduous species showed pronounced differences between arced, dorsiventrally symmetric forms in slow-growing, shaded saplings and erect, radially symmetric forms in fast growing, sunlit saplings. In contrast, the evergreen species showed little or no shift in stem orientation in relation to growth rate and tended to be more erect in shade than the deciduous species. Evergreen saplings studied at other sites were also more erect in shade than the deciduous species studied here. Within the deciduous species, the degree of arcing in shade declined with increasing leaf size and petiole length. These results, involving two congeneric pairs, suggest that stem orientation is related more to leaf dimensions and leaf habit than to taxonomic classification per se. The positioning of a single cohort of nonoverlapping leaves in shaded deciduous saplings may increase the efficiency of light interception in arced forms, as compared with evergreen saplings, where new leaves must be positioned in relation to older leaf cohorts.


"I thank the Mountain Lake Biological Station, University of Virginia, for use of facilities and partial financial support and the Lilley Cornett Woods Appalachian Ecological Research Station, Eastern Kentucky University; its manager, Robert Watts; and assistant manager, Christopher Todd Williams, for use of facilities and field assistance. Helpful comments on the manuscript were provided by Hiroaki Ishii, Takashi Kohyama, Maxine Watson, and an anonymous reviewer." (p. 1290)