Seed production and size of heaths along an altitudinal gradient in North Spain

The seed production and size of Calluna vulgaris, Erica cinerea and Erica vagans were studied at different altitudes (from coast to high mountain). There were no significant differences in seed production among species, although E. cinerea tend to produce more seeds. Seed production of the species varied between localities. A high seed production was not found at the highest altitudes for E. vagans and E. cinerea. Neither low seed production nor significant annual fluctuations were revealed for Calluna at the highest altitudes. Type of substratum seem to influence seed production of E. vagans. Its lowest seed production was on quartzite. Altitude did not seem to have an effect on seed size, however, the characteristics of soil could influence on the mean seed size. The smallest seed size of Calluna was produced on richer soils. While E. vagans showed the highest seed size on this type of soils. Annual variations in mean seed size for two species were also revealed. Seed production and seed size variations between species and sites could be related with the success of seed regeneration and present distribution patterns of these plants