Structure and dynamics of a clonal plant population: Classical model results in a non-classic formulation

The structure of a clonal plant population is studied in Calamagrostis canescens, a perennial grass colonizing forest areas which have become open due either to tree-felling or windthrow. A scale of ontogenetic stages is defined where the stages of individual plants (tussocks) are described in terms of their morphology. No strict correspondence has been revealed between the stage of the tussock and its chronological age. Therefore, the formal classification of individuals considers both the age and the stage in ontogenesis, which results in a life-cycle graph defined on a finite two-dimensional lattice. The origin of individuals (seed reproduction or vegetative propagation) has also appeared to predetermine different pathways within the life cycle. The traditional way to formally relate population dynamics to the population structure leads to a matrix model, while the special pattern of the life-cycle graph, together with that of the corresponding population vector, results in a non-traditional form of the projection matrix. This form differs from the classical Leslie and Lefkovitch ones with certain nonzero entries (vital rates), which complicates the routine mathematical analysis of the model. We demonstrate that the classical model outcomes, like the asymptotic rate of population growth (or decline), the equilibrium population structure and the reproductive values of the population groups can still be obtained from a given set of the age-stage-specific vital rates. The potential-growth indicator is also shown calculable from the vital rates and it appeared useful in a procedure of model calibration on a short series of empirical data. The model can thus serve as a research tool specialised for applied problems which may be associated with the double-structured population dynamics in a clonal plant species.