   Our Native Oaks - May 16, 2012 Jeff Schalau, Agent, Agriculture & Natural Resources University of 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 Seed Plants of Northern Arizona (by W.B. McDougall), 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 Dunn oak (Q. dunnii also called the Palmer oak, Q. palmeri) are less common. Of the less common oaks, I regularly see the Dunn oak in the Verde Valley and have not actually observed the other three but references indicate that canyon live oak can be found in Oak Creek Canyon (maybe I need to get out more). Gambel oak is found at higher elevations and is “winter deciduous”: it’s leaves are shed with the arrival of cold weather in the fall. The rest of our native oaks are found at lower elevations and are often described as “evergreen”. However, it is more accurate to describe them as “drought deciduous”. In Arizona, the months of May and June typically have little or no precipitation. During this period, the drought deciduous oaks shed many (and sometimes almost all) of their leaves to reduce water demand. This is an adaptation that allows them to conserve their resources during the driest times and reinitiated growth with the coming of our summer rains. 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 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. Large stands of shrubby Gambel oaks can be seen on the slopes of Mingus Mountain. 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. Dunn oak (Palmer oak) also has a shrubby growth form, but has dark green shiny leaves with coarse spines on the leaf margin. It is common in the foothills of the Verde Valley and on drier slopes of the surrounding mountains. 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 Hertitage live oak (Q. virginiana ‘Heritage’). Both are somewhat slow growing but perform well in our climate. Follow the Backyard Gardener on Twitter – use the link on the BYG website. If you have other gardening questions, call the Master Gardener help line in the Camp Verde office at 928-554-8999 Ext. 3 or e-mail us at cottonwoodmg@yahoo.com and be sure to include your name, address and phone number. Find past Backyard Gardener columns or provide feedback at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.  |