Demographic approaches to studies of canopy development in plants

Via their modular structure, plants operate at two levels in their population biology—the level of the individual and that of the parts which make up an individual; the genet and the ramet (sensu Harper). Thus, possibilities exist to describe the growth of plants as a population-like process rather than via the conventional notions of dry matter change and relative growth rate. This paper gives three applications of this idea. The first analyses the temporal changes in the number of vegetative and flowering shoot meristems of plants grown in different soil volumes. The main conclusion was that the ‘trade-off’ between the production of flowering or vegetative meristems was less influenced by root restriction than was the overall production of meristems. This was higher for plants grown in the largest pots. The second example is an analysis of pruning apple trees where, using bud-counts on pruned and unpruned trees, bud distribution between branches was analysed. Pruning restored a normal distribution, whereas unpruned plants had a skewed distribution of buds per branch. The final, related notion, is the development of a matrix model of bud pruning based on the prediction of the maximum harvestable yield of an animal population. Pruning and harvesting are analagous processes since both involve removal of some individuals, thus affecting the fecundity or productivity of remaining members of the population. Optimal pruning or harvesting estimates, on the basis of the age-dependent fecundity and survival of individuals in the population, the maximum number of individuals which can be removed without reducing the overall population growth rate below unity. At this point, all harvested individuals or pruned buds are replaced in the next time step. The discussion highlights directions for extending this corollary further.