Do inter-specific differences in seed size determine natural regeneration traits in pinus pinea and pinus sylvestris?

Abstract

Inter-specific difference in seed size is one of the main factors influencing regeneration strategies in plant species. The classical trade-off theory postulates that the species with larger seeds produce smaller amounts of offspring that colonize fewer microsites, although a large amount of reserves permits seeds to germinate and survive in a broader range of conditions. Contrarily, the species with smaller seeds are assumed to widely disseminate their seeds, attaining lower rates of seedling establishment and survival. We tested this hypothesis by analysing regeneration traits in Pinus pinea L. (large-seeded species, average seed weight: 700 mg, SD: ±200 mg) and Pinus sylvestrais L. (small-seeded species: average seed weight: 13 mg, SD: ±4.2 mg). We used data from regeneration trials in inland Spain to analyse five different attributes: 1) seed production and masting habit, 2) seed shadow, 3) annual pattern of emergence and seed success, 4) spatial pattern of seedling emergence, and 5) seedling survival. Our results show that those attributes defining the spatial pattern of regeneration in both species match the assumptions related to their seed size. However, when these species grow under limiting environments, the annual pattern of emergence and seedling survival does not follow the expected trade-off theory.