Local pollen dispersal and distant gene flow in Norway spruce (Picea abies [L.] Karst.)

Pollen gene flow is one of the most important factors influencing genetic structure of wind pollinated forest trees. We investigated mating system, pollen dispersal patterns and the level of pollen immigration in a clonal archive of Norway spruce (Picea abies [L.] Karst.). The plantation consisted of 114 clones originating from different (often distant) parts of Poland. We sampled 100 seeds in upper and lower crown portions of two ramets, each of five clones (totally 2000 seeds). Using allozyme markers, we estimated the parameters of reproductive system based on neighborhood model approach. We found that the level of self-fertilization was generally low (s=0.059), although statistically significant. The immigration from outside of the neighborhoods (20 m radius) was considerable accounting for more than 83% of successful fertilizations. Despite the high level of distant gene flow, pollen dispersal within neighborhoods was severely restricted to neighboring trees with a mean effective pollen dispersal distance=6.8 m (mean physical distance between mothers and potential fathers=13.1 m). In addition, mating success of individual males within neighborhoods was moderately influenced by their fecundity and direction of their location relative to mother trees. The mean effective number of outcross males within neighborhoods was low (Ne=6.71), which is about 7.5% of the mean number of potential males (90). The mating parameters were similar in upper and lower crown levels. The implications of reproductive patterns of clonal archives for ex situ conservation programs are briefly discussed.