The applicability of traditional models of life-history evolution is restricted because models assume constant environments without density-dependence. In these models the geometric growth rate Q,) of a lineage is the natural choice for the fitness criterion. Because in growing populations ~ is very sensitive to changes in generation time, biennials appear at a disadvantage when compared to species with annual reproduction. We propose an alternative fitness criterion for the situation in which recruitment is limited by both the availability of seeds and the (constant) rate at which 'safe sites' for establishment are created by small-scale disturbances. Under the assumptions of the model the evolutionarily stable strategy is to maximize expected seed production, irrespective of the length of the life cycle. For monocarpic plants, this implies that delay of flowering is favourable if the increased seed production compensates for the death of rosettes. * Publication of the Meijendel comit6, New series No. 89. ** Nomenclature follows Heukels & van der Meijden (1983), Flora van Nederland, Wolters Noordhoff, Groningen. *** We would like to thank Prof. K. Bakker, Dr Nora Croin Michielsen, Dr E. van der Meijden and Dr M. Sabelis for their comments on a number of previous drafts.