Seasonal model of modular growth in plants

1. Modules are important to plant growth because they have the meristems needed to produce daughter units. The module dynamics of single plants are examined in a model developed to evaluate the relative importance of seasonality and reproductive effort. The model is a logistic system in which K is the maximum number of modules per plant and r(t), the instant growth rate, is the capacity of modules to multiply under optimal conditions minus the costs of seasonality and flowering. 2. Simulations included adverse seasons varying in severity and frequency, different timings of births and deaths of modules, different flowering times and reproductive efforts, different performances under optimal conditions, and different maximum plant sizes. 3. Of all the parameters in the model, only the capacity to multiply and the combined costs of flowering and climatic severity had a substantial impact on early plant size. The rate of module accumulation slowed when plants got close to maximum size. Mathematically complex frequencies, timing and delays in mortality, growth and flowering can be disregarded. 4. The capacity to multiply vegetatively (r.sub.v) should be measured in newly emerged seedlings growing under optimal conditions. before the onset of negative size-dependent factors. Producing daughter modules early in the life of modules should be favoured when rapid growth is crucial. The value of [r.sub.v] limits the amount of reproductive effort, [Phi), and seasonal severity, [Sigma], that a plant can sustain. Plants should show increased reproductive effort at the climatically benign end of their range. Key-words: module demography, seasonality, reproductive episodes, reproductive effort Journal of Ecology, 1992, 80, 123-130