Reproductive strategies of six herbaceous perennial species in relation to a successional sequence.

Dry weight allocation to vegetative and reproductive structures in six perennial herbs was studied at three successional sites (quarry, grassland and scrub) on the magnesian limestone in County Durham, England, during the summer of 1978. Two species showed little difference between sites but the other four all displayed the same pattern. Population reproductive effort was highest in the quarry and lowest in the grassland. Reproductive effort of flowering individuals however was the same at all three sites, so that between-site differences in population reproductive effort were entirely a consequence of variation in the proportion of plants which flowered. Indirect evidence suggests that initiation of flowering may be triggered by the attainment of a critical leaf weight. It is suggested that the between-site differences can be explained in terms of the levels of competition at each site and that reproductive effort does not necessarily decline uniformly during succession.