Phenology, dichogamy, and floral synchronization in a northern red oak (Quercus rubra) seed orchard

We developed a novel scoring system to assess spring phenology in a northern red oak (Quercus rubra L.) clonal seed orchard. The system was used to score from 304 to 364 ramets for three reproductive seasons and to place clones into early, intermediate, and late phenology classes. Although the absolute number of clones in each phenological class changed from year to year, the overall order of clonal flowering was highly stable (rₛ = 0.67, p < 0.001). Early-flowering clones flowered significantly longer than later flowering clones in all 3 years. Dichogamy was present in the orchard, with male flowers of a clone emerging from 1.4 to 3.0 d sooner than its female flowers. Mean dichogamy values for individual clones ranged from 0.0 to 4.9 (± 1.3) d. Year strongly influenced a clone’s dichogamy value (F = 6.0, p = 0.004), whereas genotype had no influence. The mean overall phenological synchronicity for the 3 years of observations was 0.30 ± 0.01 or about 30% overlap between the time when females were receptive and males were shedding pollen. This study represents the first effort to quantify phenology in an artificial population of northern red oak, and it provides a snapshot of the current relationship between temperature, phenology, and floral synchronization.