Phototropism of Whole Trees: Effects of Habitat and Growth Form

Abstract

The hypothesis that phototropism applies to entire trees as well as to apical meristems was tested. The hypothesis was correct but with important modifications: (1) canopy emergent species exhibit very little phototropic response; (2) streamside species exhibit significantly more response than upland species. Costs and benefits of learning are shown to provide an evolutionary explanation for these differences. Extrapolation of the cost/benefit model yields predictions about what habitats are likely to select for phototropic response.