   Central Arizona’s Oak Species - June 15, 2005 Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County The oak family (Fagaceae) includes over 600 species which are distributed across the temperate zones of North America, Europe, Asia, and even south into Polynesia. Oak trees often have historic/aesthetic value and, in many places, they are important for timber. Oak wood is durable, tough, and attractively grained. It is especially valued in shipbuilding, flooring, furniture, railroad ties, barrels, tool handles, and veneer. The bark of some oaks has been used in medicine, tanning, and for cork and dyes. Acorns, the fruit of oak trees, have long been a source of human and animal food. According to McDougall (author Seed Plants of Northern Arizona), north central Arizona has eight species of true oak. Identifying individual species can be tricky as they are known to intergrade (hybridize) with each other. In my experience, four Quercus species are fairly common in our general area. These are: Emory oak (Quercus emoryi); Arizona white oak (Q. arizonica); Gambel oak (Q. gambelii); and shrub live oak (Q. turbinella). The other four species: canyon live oak (Q. chrysolepis), net-leaf oak (Q. reticulata), wavyleaf oak (Q. undulata), and Q. dunnii are less common. Emory oak has dark green, oblong, shiny leaves with spines at the margins (leaf edges). The bark is black on mature trees. It can exist as a shrub or a tree, but can reach a height of 40 feet or more and trees often have very upright growth habit. It is drought-deciduous (loses it leaves during the May-June dry season) and grows between 3,000 to 8,000 ft elevations. Arizona white oak has pale green leaves which often have marginal spines, but may also be smooth or rounded. The bark is whitish on mature specimens (hence the name). It can exist as a shrub or a tree, but can reach a height of 40 feet or more and trees often have a spreading/rounded growth form. It is drought-deciduous and grows up to 7,500 ft elevation. Gambel oak is one of the easiest species to recognize having deeply lobed, “typical” oak leaves. The bark is grayish in color. It also can exist as a shrub or a tree, but can reach a height of 40 feet or more. It is the only winter deciduous oak we have and grows between 5,000 to 8,000 ft elevations. Shrub live oak (or scrub oak) leaves are very similar in appearance to Arizona white oak. It seldom grows higher than 8 to 10 ft and is a major component of the interior chaparral vegetation type. It is drought-deciduous and grows up to 8,000 ft elevations. Canyon live oak has medium green leaves with marginal spines. The leaves are rounder than those of Emory oak. I have not seen a large, native-grown tree specimen in Arizona. However, I have seen some young specimens at the base of Mingus Mountain near Cottonwood. This oak species is very common in the mountain ranges of California and southern Oregon. Scattered populations occur in the mountains of southwestern Nevada and in parts of western and central Arizona, and Mexico. Fossil evidence suggests that this oak was much more widely distributed to the east during the late Wisconsin and early Holocene. Oaks also make excellent landscape trees. However, the native species discussed above are not often cultivated due to their slow rates of growth. I can suggest two suitable species that are available in nurseries: Texas red oak (Q. buckleyi) and southern live oak (Q. virginiana). Both are somewhat slow growing but perform well in our climate. Two final notes: the numerous small brown bugs that have been reported in the Verde Valley are false chinch bugs. They are not a threat to landscape plants and were described in the June 6, 2001 Backyard Gardener column (which is available online – see web address below). Also, curly top virus has recently been reported on tomatoes in Camp Verde. Watch your tomato and pepper plants for stunted growth and rolled leaves. Refer to the July 28, 2004 Backyard Gardener column for more information on curly top virus. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/. |