Biomass production, structural deformation, selfthinning and thinning mechanisms in monocultures

Abstract

Consideration is given to the production of biomass in three of the possible growth phases that may be experienced by plants at various spacings in stand monocultures. The amount of radiant energy available for this is related to canopy surface area, volume, and slenderness, and the efficiency with which the operation is performed. The unified non-dimensional formulae established describe normal natural growth, growth with plastic deformation, and growth subject to the self-thinning process, which occurs when individuals are packed too closely together. The formulae define growth surfaces for the life-lines followed by individual plants, and for the rounding and smoothing of these lines that occurs, at the otherwise sharply defined growth phase boundaries, as a result of the statistical uncertainties in specifying plant dimensions and numbers in spacetime. The results provide an explanation of features of the self-thinning process and the values of the constants and parameters associated with approximate power law descriptions of the phase boundary on which it takes place. A quasi-static analysis of growth and thinning mechanisms indicates one-sided competition coexistence conditions for plants in distributions with uniformly augmented and diminished biomass, and the boundaries separating and distinguishing diminished biomass states from which recovery to further growth is, or is not, possible. Because of the dependence of events in the growth process on canopy shape and volume a preliminary classification of suitable geometric forms is given, together with formulae for evaluating the required quantities, for several cases of interest.