Reproductive variability in Pinus sylvestris in southern France: Implications for invasion

Though fecundity and dispersal have been recog- nized as major factors in most invasion models, their ecologi- cal determinants are still poorly known. This paper aims to identify the main sources of variation in seed production and dispersal distance in a naturally expanding Pinus sylvestris population. We propose some tree measurements that may be related to their contribution to population expansion. We quantified cone and seed production and measured three seed characteristics related to their dispersal ability: mass, wing area and wing-loading (mass:area ratio) in cones sampled at different relative heights and aspects in the canopy and in trees of different age and competitive status. Results showed that isolated trees had a much more abundant cone production, which was more evenly distributed in the canopy than trees within stands. Age was also positively related to cone produc- tion. Seed dimensions varied between and within trees but we found no effect of isolation or age. The strong positive corre- lation between wing area and seed mass leads to a limited variability of seed wing loading. Seed characteristics may thus play a minor role in individual dispersal ability and relative tree position in the stand that is strongly linked to tree fecun- dity should be more appropriate for estimating the individual contribution to the whole population expansion. Our results also highlight the importance of obtaining demographic data in low-density populations to estimate the invasive potential of a species.

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