Model of Above-ground Assimilate Partitioning and Growth of Individual Trees in Even-aged Forest Monoculture

A model in two parts is developed to predict annual, above-ground biomass growth of individual trees in even-aged forest monoculture. The first part predicts what proportions of the assimilate produced by the tree by photosynthesis are partitioned between leaves, branches and stems. The method used draws on earlier suggestions that there are functional relationships between the plant parts which determine the assimilate partitioning. However, the relationships identified in the earlier work were strictly limited in number leading to simple mathematical techniques to determine partitioning. In the present work, it is recognized that the number of functional relationships between the various parts is not necessarily limited and that these relationships, together with other biological requirements of growth, all act as constraints on assimilate partitioning. Mathematical expressions for these constraints are developed from appropriate functional relationships between above-ground tree parts (leaves, branches and stems) and other biological considerations. A linear programming approach is then used to determine the partitioning proportions by assuming that trees adopt a growth strategy of maximizing leaf production. The second part of the model involved little novel development and predicts the biomass growth and dynamics of the trees in the stand. Application of the two parts of the model in a Eucalyptus regnans F. Muell plantation forest suggests that it describes realistically the known growth dynamics of individual trees in even-aged forest monoculture.