Reproductive variability in Pinus sylvestris in southern France: implications for invasion
Variabilité de la capacité de dispersion dans une population de Pinus sylvestris du sud de la France : implications pour l`invasion
Résumé
Though fecundity and dispersal have been recognizedas major factors in most invasion models, their ecologicaldeterminants are still poorly known. This paper aims toidentify the main sources of variation in seed production anddispersal distance in a naturally expanding Pinus sylvestrispopulation. We propose some tree measurements that may berelated to their contribution to population expansion. Wequantified cone and seed production and measured three seedcharacteristics related to their dispersal ability: mass, wingarea and wing-loading (mass:area ratio) in cones sampled atdifferent relative heights and aspects in the canopy and in treesof different age and competitive status. Results showed thatisolated trees had a much more abundant cone production,which was more evenly distributed in the canopy than treeswithin stands. Age was also positively related to cone production.Seed dimensions varied between and within trees but wefound no effect of isolation or age. The strong positive correlationbetween wing area and seed mass leads to a limitedvariability of seed wing loading. Seed characteristics may thusplay a minor role in individual dispersal ability and relativetree position in the stand that is strongly linked to tree fecundityshould be more appropriate for estimating the individualcontribution to the whole population expansion. Our resultsalso highlight the importance of obtaining demographic datain low-density populations to estimate the invasive potentialof a species.