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ARS Home » Northeast Area » Washington, D.C. » National Arboretum » Floral and Nursery Plants Research » Research » Publications at this Location » Publication #317189
Title: Phenology, dichogamy, and floral synchronization in a northern red oak (Quercus Rubra L.) seed orchard

Author
item Alexander, Lisa
item WOESTE, KEITH E - Forest Service (FS)

Submitted to: Canadian Journal of Forest Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2015
Publication Date: 2/2/2016
Citation: Alexander, L.W., Woeste, Keith E. 2016. Phenology, dichogamy, and floral synchronization in a northern red oak (Quercus Rubra L.) seed orchard . Forest Ecology and Management. 46:629-636.

Interpretive Summary: We used a novel floral rating system to determine the relative influences of genetics and environment on phenology, dichogamy, and floral synchronization in a northern red oak seed orchard. Year influenced leaf out date more than subline location or genotype, indicating that environmental factors at flowering time strongly regulated absolute flushing date. Temperature had a clear effect on the duration of flowering in the seed orchard, where early clones flowered significantly longer than later flowering clones in all three years. Dichogamy was present in the orchard with male flowers of a clone emerging between 1.4 and 3.0 days sooner than its female flowers. The mean overall phenological synchronicity for the three years of observation was 0.30±0.01, or about 30% overlap between all receptive females while males were shedding pollen. We believe that this rating system and analysis software could be widely adopted by seed orchard managers to facilitate management, add to basic understanding of red oak phenology, and provide a tool for comparisons among seed orchards. The quantification of phenological synchronization is also fundamental in making decisions regarding orchard rouging, supplemental mass pollination, or controlled pollinations within an orchard managed to attain high levels of genetic diversity in seed orchard progeny.

Technical Abstract: We developed a novel scoring system to assess spring phenology in a northern red oak clonal seed orchard. The system was used to score between 304 and 364 ramets for three reproductive seasons and place clones into early, middle, and late phenology groups. While the absolute number of clones in each phenological class changed from year to year, the overall order of clonal flowering was highly stable (r = 0.67, p < 0.001). The average length of pollen shed for a clone was 10 days; the average length of a clone’s female flower receptivity was 9.5 days. Temperature had a clear effect on the duration of flowering in the seed orchard, where early clones flowered significantly longer than later flowering clones in all three years. Dichogamy was present in the orchard with male flowers of a clone emerging between 1.4 and 3.0 days sooner than its female flowers. Mean dichogamy values for individual clones ranged between 0.0 and 4.9±1.3 days. Year strongly influenced a clone’s dichogamy value (F=12.8, p<0.001) while genotype had no influence. The mean overall phenological synchronicity for the three years of observation was 0.30±0.01, or about 30% overlap between all receptive females while males were shedding pollen. In all years, late flowering males had the highest phenological overlap (PO) values, followed by intermediate males. Early flowering males had the lowest PO. Female flowers had the opposite pattern – early flowering females had the highest PO values while late flowering females had the lowest PO. This represents the first effort to quantify phenology in an artificial population of northern red oak and provides a snapshot of the current relationship between temperature, phenology, and floral synchronization.