Flowering phenology as an essential parameter for pollen flow modelling in Populus nigra L

International audience; European black poplar (Populus nigra L.) can be found in three interconnected ecosystems: (i) natural riparian forests, (ii) cultivated stands through P. ×euramericana interspecific hybrids, and (iii) ornamental plantings through P.nigra cv. ‘Italica’ (i.e., Lombardy poplar). As a first step to assess the potential impact of cultivated and ornamental poplars on the genetic diversity of wild populations, pollen flow was modelled within a wild P.nigra stand located at close vicinity of a Lombardy poplar row. An inventory of 484 wild P. nigra adult trees was realized on this 11.5 ha study site located along the Loire River. Several physical and biological parameters such as flowering phenology, physical distance, and tree size were measured on all trees. Pollen flow was estimated by collecting 1680 seeds from 31 females distributed over the site, and by modelling pollen dispersal using mating model and paternity analysis based on 10 SSR markers. We detected a high immigration rate (45%), and 4% of the seeds could be attributed to Lombardy poplars. The model that best fitted the data involved an exponential power distribution curve with a fat-tailed dispersal kernel. Phenological assortative mating and short distance pollen dispersal were identified as the main factors influencing reproductive success and hybridization between Lombardy and wild poplars.