The importance of the height of the lowest living branch or fork, also called the morphological inversion point, is stressed by Ogawa (1965), Hallé et al. (1978) and Oldeman (1974b, 1989). It provides an easily measurable ratio between crown depth and total height. Empirically, Hallé et al. (1978) established that a ratio greater than one half indicates a free-standing, not shaded, tree. A ratio of about one half indicates trees that have recently entered a phase of vigorous growth. A value less than one half is evidence of diminished vigour, by suppression or by senescence. Hallé et al. consider the morphological inversion points collectively as the morphological inversion surface. This surface gives a topographical indication of the distribution of either vigorous, recently established, or senescent canopy trees. Lescure (1978) used the morphological inversion surface for characterization of secondary tropical rainforest development in French Guiana. Hallé et al. (1978) suggest that the position and nature of this inversion surface might have a bearing on microclimate regulation. Light and humidity gradients with height are modulated by the canopy architecture. These modulated gradients show microclimatic “inversions” from less or more than such light intensities as average extinction would account for at a certain level in the forest, and also from more or less than average humidity build-up. The collected points where these inversions take place can be thought of as forming an ecological inversion surface. Hallé et al. thus emphasize that efforts should be made to relate the morphological to the ecological inversion surface.
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