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Biology And Ecology

Found in a wide variety of habitats, oaks prefer loamy, well drained soils. The roots are quite extensive, reaching out at least three times the height of the tree and down as deep as 15-40 ft (4.6-12.2 m), depending on site conditions.

There are both evergreen and deciduous species. Each leaf of the evergreen oaks falls after one to two years, but there is no synchronous leaf loss. New leaves form during either the first spring growth or a smaller secondary flush of growth which can occur when conditions are favorable. Deciduous oaks follow the typical pattern of fall leaf loss in response to decreased daylight, winter dormancy, and spring flush of new leaves and flowers.

Oaks vary in size from small shrubby species to trees with majestic dimensions. The tallest oak, reaching up 123 ft (37.5 m), with a circumference of 21.6 ft (6.6 m) and a canopy spread over 83.6 ft (25.5 m) is a black oak found in Warrensville Heights, Ohio. Other oaks notable for their size are: the Wye live oak (Q. virginiana) in Maryland standing 91.8 ft (28 m) tall; a 106.6-ft (32.5 m) tall coast live oak (Q. agrifolia) in Chiles Va Mey, California; and a northern red oak (Q.rubra) in Ashford, Connecticut, standing 77 ft (23.5 m) tall and spreading 105 ft (32 m).

Relying primarily on wind pollination, massive quantities of pollen are produced in the male flowers (25-100 per catkins) each spring. The female flowers tucked inconspicuously in the nodes of axial twigs mature a little later, avoiding self-pollination. Either single or clusters of two to three acorns begin forming. Most trees begin acorn production after 20 years. Crop production varies yearly according to numerous factors, but an individual tree can produce over 5,000 nuts in a good year. Of these, roughly 25% are likely to be infested with weevils, making them inedible and unviable.

Because of their huge investment in acorn production, oaks play a critical role in supporting wildlife and maintaining regional biodiversity. Many migratory species of birds and bats roost or nest in them, in addition to using the food resource. In California, it is estimated that over 5,000 species of insects, more than 80 species of reptiles and amphibians, 150 species of birds, and over 60 species of mammals rely upon oaks for some part of their lifecycle. Acorn or mast production is such a significant element of most oak ecosystems that crop failure can be life threatening for many species.

Additional topics

Science EncyclopediaScience & Philosophy: Nicotinamide adenine dinucleotide phosphate (NADP) to Ockham's razorOaks - Evolution, Biology And Ecology, Diseases, Distribution, Historic Importance, Acorns, Wood, Ecological Significance - Economic importance