White Oak...
Flowering and Fruiting- White oak flowers in the spring at about the same time leaves appear. The time may vary from late March to late May depending upon latitude. It is monoecious; flowers of both sexes are present on the same tree. The yellowish staminate flowers appear first and are home in 5- to 8-cm (2- to 3-in) catkins. The reddish pistillate flowers appear 5 to 10 days later either singly or in pairs on short stalks. Female flowers that are not fertilized abscise during the development period. High abscission rates are common and may be related to weather conditions during the period of pollination, ovule development, and fertilization (44). Ripe anthers open and close with changes in relative humidity. Normally, pollen dissemination is completed within 3 days but periods of wet weather delay pollen shedding. Dry winds and freezing weather are also detrimental to flower development and pollen shedding (28). Acorn crops are good in years when the weather is warm for 10 days during flowering and then cool for 13 to 20 days afterward. The acorn crop has been poor in years when cool periods preceded warm periods at the time of flowering (36).
Acorn maturity is reached approximately 120 days after pollination. Acorn drop follows 25 days later and is complete within a month. Physiological maturity, as indicated by normal germination, is reached when acorns change color from green to light brown (4). Acorns germinate almost immediately after falling to the ground in September or October.
Seed Production and Dissemination- White oak can produce seeds prolifically, but good acorn crops are irregular and occur only every 4 to 10 years. Sometimes several years may pass without a crop. Acorn yields range from 0 to 500,000 acorns per hectare (202,000/acre) (7,22,28). This great variation in acorn production exists not only among isolated stands of oaks but also among individual trees within stands and from year to year.
Trees normally bear seeds between the ages of 50 and 200 years, sometimes older; however, opengrown trees may produce seeds as early as 20 years. Individual white oak trees tend to have either very good or very poor seed crops and are noticeably consistent in seed production from year to year (20,28,36,40). A recent study (13) showed that white oak flower production varies not only annually but also among trees within a given year and that much of the variation in acorn production can be related to flower abundance at the time of pollination. More than 23,000 acorns were produced during a good seed year by an individual white oak tree growing in Virginia; it was 69 years old, 63.5 cm (25 in) in d.b.h., and 21 in (69 ft) tall, and had a crown area of 145 m² (1,560 ft²) . Average production in good years for individual forest-grown trees, however, is probably no more than 10,000 acorns.
Several studies have shown that only a small portion of the total mature acorn crop (sometimes only 18 percent) is sound and fully developed; the remainder is damaged or destroyed by animals and insects (15,28,40). However, some damaged acorns germinate if the embryo is not damaged. Light acorn crops are often completely destroyed by animals and insects, so seedlings are produced only during heavy crop years.
Seeds are disseminated by rodents (chiefly squirrels and mice), gravity, and wind. The area seeded by individual trees is small and therefore widespread reproduction depends on adequate distribution of seedbearing trees.
