You can find numerous types of oak trees around the world. In north america and especially in Virgina, our Tree Experts of Charlottesville have seen some common species which include northern red oak (quercus rubra), white oak (quercus alba) and coast live oak (quercus agrifolia). Oak is the common name for many acorn-producing trees and shrubs that are members of the beech, or fagaceae, family. Oak trees are classified as members of the genus quercus, a latin word said to be derived from a celtic word meaning “fine tree. ” worldwide there are more than 600 different species of oak. They thrive across the northern hemisphere in china , japan , europe , the british isles , and in all of the continental united states except for alaska.
More than half of the 600 species are native to north america. Yet only about 60 varieties grow north of mexico. In the forests of northern areas that have short summer growing seasons and long winters, such as canada , northern europe, and siberia , varieties of oak are very scarce.
Identify an Oak by Leaf Shape
In many cases an oak’s leaf shape and its geographic location together provide a pretty good indication of species. For example, a wild-growing oak with heavily lobed leaves in the southern rocky mountains or colorado plateau can only be the gambel oak; in the pacific northwest, such a tree can only be the garry oak (a. K. A. Oregon white oak). Even within a given geographic area, ecological setting or habitat can give you confidence in identifying certain oaks by leaf shape. An oak leaf in the deep south is probably that of a water oak if you find it in bottomland woods, and probably that of a blackjack oak if you encounter it along a dry ridgecrest.
Red Oak Tree Group
Where do willow oak trees grow? they thrive in floodplains and near streams or marshes, but the trees are remarkably drought tolerant, too. One of the interesting facts about willow oak trees is their relation to red oaks. They are in the red oak group but do not have the characteristic lobed leaves of the red oaks. Instead, willow oaks have narrow willow-like leaves with a bristle-like hair at the end of the foliage that characterizes them as oaks.
The white oak group, called botanically leucobalanus, is one group. In this the white oak, quercus alba, is the predominant species. It also includes post, bur, swamp white, chinquapin, over cup, and swamp chestnut oak. These species provide the so-called sweet mast. Their acorns mature in one year, are less bitter, and germinate in the fall. Buds are rather rounded. The bark is light gray in color and rather flaky. Leaves are lobed or wavy along the edges but the lobes and ends of the leaf are rounded and smooth. The wood cells of these trees are coated inside with a plastic-like substance called tyloses. This makes the wood waterproof and accounts for its use in barrels, buckets, and ships. White oak wood is most durable.
The red oak sapling can survive in partial shade but eventually requires full sun to reach its maximum height. The best setting for a red oak is in sandy loam that has a tendency to be either neutral or somewhat acidic. Water this species on a regular basis, especially as it grows. The tree is a northern species and it will not fare as well in warmer climates. Expect heavy crops of acorns every two to five years. Transplanting red oaks is usually problem-free.
The White Oak Tree Group
The white oak is a large, strong, imposing specimen. It has a short stocky trunk with massive horizontial limbs. The wide spreading branches form an upright, broad-rounded crown. The bark is light ashy gray, scaly or shallow furrowed, variable in appearance, often broken into small, narrow, rectangular blocks and scales. The leaves are dark green to slightly blue-green in summer, brown and wine-red to orange-red in the fall. The fall foliage is showy. Oaks are wind pollinated. Acorns are produced generally when the trees are between 50-100 years old. Open-grown trees may produce acorns are early as 20 years. Good acorn crops are irregular and occur only every 4-10 years.
The white oak prefers full sun, but has a moderate tolerance to partial shade. It is more shade tolerant in youth, and less tolerant as the tree grows larger. It can adapt to a variety of soil textures, but prefers deep, moist, well-drained sites. High ph soil will cause chlorosis. Older trees are very sensitive to construction disturbances. The deep tap root can make transplanting difficult. Transplant when young. New transplants should receive plenty of water and mulch beneath the canopy to eliminate grass competition. Old oaks on upland sites can be troubled by sudden competition from and excessive irrigation of newly planted lawns. Their root zones must be respected for them to remain healthy. White oak is less susceptible to oak wilt than the red oak species.