FOLIAGE PROFILE, SIZE STRUCTURE AND STEM DIAMETER PLANT HEIGHT RELATIONSHIP IN CROWDED PLANT-POPULATIONS

The relationships between vertical foliage profile of an individual pl ant, competition between individuals, size structure and allocation pa ttern between stem diameter (D) and plant height (H) were investigated using canopy photosynthesis and two-dimensional continuity equation m odels including D and H as two independent variables. Broad-leaved typ e plants (more foliage mass in the upper layer than in the lower layer of the canopy of an individual when grown in isolation) showed curvil inear D-H relationship and bimodal H distribution, and underwent more asymmetric competition than coniferous type plants (more foliage mass in the lower layer than in the upper layer of the canopy of an individ ual when grown in isolation) under crowded conditions. Coniferous type plants showed almost linear D-X relationship (i.e. simple allometry) and unimodal H distribution, and underwent more symmetric competition than broad-leaved type plants under crowded conditions. However, in bo th the cases D distributions were unimodal. Allocation patterns betwee n D and H affected these features only a little. These simulation resu lts can explain many actual data already published. The value of eta f or an individual plant (foliage profile parameter of an individual can opy representing a species-specific branching pattern and canopy morph ology when grown in isolation) governs size structure (bimodal or unim odal), the mode of competition, D-H relationship and mean D-mean H tra jectory with time under crowded conditions. Therefore, a simple view o f the competition-allometry relationship that competition determines a llometry should be re-evaluated incorporating the foliage profile of a n individual. These theoretical results should also be important when studying species coexistence. The canopy tends to be multi-layered in broad-leaved type plants and mono-layered in coniferous type plants. T herefore, it is hypothesized that species coexistence in the former is mainly by way of separation of vertical space (i.e. niche separation under strongly asymmetric competition) and that species coexistence in the latter is due to nearly symmetric competition in a single canopy layer. (C) 1995 Annals of Botany Company