The cork oak, Q. Suber, the bark of which yields cork (q.v.), is a native of the west Mediterranean area. In Spain the wood is of some value, being hard and close-grained, and the inner bark is used for tanning.
The valonia of commerce, one of the richest of tanning mate rials, is the acorn of Q. Aegilops, a fine species indigenous to Greece and the coasts of the Levant.
Some oaks are of indirect importance from products formed by their insect enemies. Of these the Aleppo gall (see GALLS) is yielded by Q. infectoria, a native of Asia Minor and western Asia. Q. coccifera, a small bush growing in Spain and many countries around the Mediterranean, furnishes the kermes dye. (See KERIVIES.) Q. persica, or according to some Q. mannifera, attacked by a small insect (Coccus sp.) yields a sweet exudation which the Kurds collect and use as manna (q.v.).
In North America the oaks are generously represented. They attain their greatest size and economic importance in the southern United States, especially in the lower Mississippi valley, and reach their maximum diversity as regards species in the highlands of Mexico, notably in the western Sierra Madre range, where they form vast forests. In a recent monograph (The American Oaks, 1925), W. Trelease enumerates 371 species, of which 253 occur in Mexico, 54 in Central America, 3 in Panama, 4 in Colombia, and 1 in the Antilles (Cuba), while 84 are found in the United States, To extending into the southern border of Canada. These vary greatly in size from small, straggling or even creeping shrubs, to magnificent forest trees, 150 ft. or more in height, with trunks exceeding 6 ft. in diameter. In addition Trelease recognizes more than 5o named hybrid oaks whose parent species are regarded as satisfactorily determined.
The American oaks fall into two main groups—the white oaks and the red or black oaks—about equal in number and comprising practically all the species. In the white oak group (Leucobalanus) the acorns ripen at the end of the first season, the shell of the nut is smooth inside, and the leaves or their lobes, which are usually rounded, are without bristle tips. In the black or red oak group (Erythrobalanus) the acorns ripen at the end of the second season, the shell of the nut is hairy inside, and the leaves or their lobes, which are usually sharp-pointed, have bristle tips.
Of the oaks found in the United States, upwards of 5o species attain the stature of trees, more than half of which are of eco nomic value for timber or other useful purposes. Fully 20 species attain a height of ioo ft. or more, and 5 equal or exceed a height of 1 so ft., with correspondingly massive trunks. These larger oaks constitute the chief supply of native hardwood lumber in North America. Three-fourths of them occur east of the Rocky Mountains; the others are found in the Pacific States, chiefly in California, the quality of their timber in general being inferior to that of the eastern oaks.
Among the most valuable eastern white oaks are the typical white oak (Q. alba), 8o ft. to ioo ft. high, with a trunk 3 ft. to
4 ft. in diameter, one of the finest North American trees; the rugged massive bur oak (Q. macrocarpa), sometimes 17o ft. high, with a trunk 6 ft. to 7 ft. in diameter; and the chestnut oak (Q. montana), the post oak (Q. stellata), the overcup oak (Q. lyrata), and the swamp chestnut or basket oak (Q. Prinus), all growing to a height of Ioo ft. and highly valued for lumber. Noteworthy representatives of the eastern red or black oak group are the red oak (Q. borealis), sometimes 150 ft. high; the Shumard red oak (Q. Shumardi), 120 ft. high; the black oak (Q. velutina), i5o ft. high, and the somewhat smaller scarlet oak (Q. coccinea) and willow oak (Q. Phellos), all important timber trees.
The oaks of the Rocky Mountain region are mostly small trees, often becoming shrubby at the higher elevations. The Rocky Mountain white oak (Q. leptophylla), rarely 45 ft. high, is the largest Colorado oak, and the Arizona white oak (Q. arizonica), sometimes 6o ft. high, is the chief oak of New Mexico and Arizona.
In California some 15 species of oak occur. Among the decidu ous kinds are the valley oak (Q. lobata), often ioo ft. to 125 ft. high, sometimes with a massive trunk io ft. in diameter; the Oregon white oak (Q. Garryana), 6o ft. to ioo ft. high, found from San Francisco bay to British Columbia, and the California black oak (Q. Kelloggii), sometimes zoo ft. high, found also in Oregon. Among the evergreen species are the coast live oak (Q. agrifolia) and the interior live oak (Q. Wislizenii), both medium sized trees; the scrub oak (Q. dumosa), usually 2 ft. to 8 ft. high, abundant in the chaparral (q.v.), and the maul oak (Q. clirysole pis), sometimes branching into an immense crown 150 ft. across, and sometimes growing erect to a height of i io feet.
The only evergreen species of the eastern States is the live oak (Q. virginiana), found near the coast from Virginia to Texas; it grows to a height of 75 ft., usually branching near the buttressed base into a round-topped head, sometimes 13o ft. across. The very strong wood was formerly much used in ship building.
The total cut of oak lumber in the United States in 1925 was 2,129,181,000 bd.ft., valued at the mill at $78,779,698, 55% of which was cut in Arkansas, Tennessee, Louisiana, West Virginia and Mississippi. Commercially oak lumber is classified as white oak and red oak. White oak lumber is cut principally from the white, chestnut, post, bur, overcup and swamp chestnut oaks; red oak lumber is cut chiefly from the red, Shumard red, scarlet, black and willow oaks.