Mating success in a coastal Douglas-fir seed orchard as affected by distance and floral phenology

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Abstract
The effect of distance and stage of phenological development on cross-pollination in a Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seed orchard was investigated by estimating the proportion of viable embryos resulting from fertilization by designated male trees. The pollen source was identified by unique allozyme genetic markers that occurred in two clones in the orchard. In 38 mother trees, the proportion of embryos fertilized by the male marker ranged from 0 to 71.4%. Very little pollen was dispersed beyond 30 m. Within 30 m, mating success was only weakly associated with distance. Multiple regression analyses determined that phenological factors strongly influenced mating patterns; nearly one-third of the variation was dependent on a phenological variable (LMmf), which measured the combined effects of floral overlap and relative pollen fecundity of potential male parents. The interaction between LMmf and distance was highly significant, indicating that the floral status of mating pairs had a strong influence on the effect of distance. Our results suggest that a lack of complete floral synchrony between near neighbors may reduce preferential mating and thus help to promote cross-fertilization within Douglas-fir seed orchards.

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