Pollen-mediated gene flow on the landscape level is investigated by using results of a three-dimensional mesoscale atmospheric meterology and transport model. The interpretation of simulated physical pollen dispersion is based upon the pollen-ovule ratio, which is the ratio between the settled pollen quantities and the number of receptive female flowers. This provides the inference of effective gene flow from potential gene flow data. Apart from the meteorological conditions of the flowering days, which shape the pollen dispersion pattern, the spatial extent of gene flow depends on the strength of the pollen sources, and on the availability of female flowers in the settling area of the pollen. If the pollen production amounts to 2.5 billion pollen per m2 forest the analysis of simulated pollen flow indicates effective gene flow at very low frequencies up to 100 kilometres downstream of the investigated oak stand. A high pollination frequency occurs only in the proximity of the oak stands. Sensitivity analysis of the total pollen production on the effective gene flow pattern shows that an increase of the pollen production promotes in particular the pollination close to the emitting stand, while long distance gene flow is lesser promoted. In fragmented tree populations, a low production restricts frequent gene flow within populations, while high values bridge the forest fragments on the landscape level.
