   Our Native Oaks - February 19, 2020 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, barrel making, tool handles, and veneer. The bark of some oaks has been used in medicine, tanning, for cork and in 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 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. 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 usually 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 reinitiate growth with the coming of 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 have smooth leaf margins. 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. Canyon live oak is related to the live oaks in California. It has medium green leaves and grows as a tree up to 80 feet or as a dense shrub up to 15 feet. Has a short trunk, 1 to 3 feet in diameter with large, horizontal, spreading branches and a rounded, broad crown. 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 in our area 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 often very similar in appearance to Arizona white oak, but tend have pricklier margins. 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 species suitable for the Verde Valley: Texas red oak (Q. buckleyi) and Hertitage live oak (Q. virginiana ‘Heritage’). Both are somewhat slow growing but perform well in our climate. See links below for photos and descriptions of our native oaks. You can follow the Backyard Gardener on Twitter – use the link on the BYG website. If you have other gardening questions, call or email the Master Gardener help line in the Prescott (928-445-6590/prescottmg@gmail.com) or Camp Verde (928-554-8992/verdevalleymg@gmail.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/. 
Arizona White Oak (Quercus arizonica) composite photo: entire tree (left, photo by Sue Smith); acorn and leaves (upper right, photo by Sue Smith); and bark (lower right, photo by Jeff Schalau).Additional Resources The Yavapai County Native & Naturalized Plants database currently has photos and descriptions of over 832 native plants. This project was created by Yavapai County Master Gardeners to help Arizona residents in learning to recognize and appreciate our unique flora. cals.arizona.edu/yavapaiplants/ Emory Oak (Quercus emoryi) Yavapai County Native & Naturalized Plants, University of Arizona Cooperative Extension cals.arizona.edu/yavapaiplants/SpeciesDetail.php?genus=Quercus&species=emoryi Arizona White Oak (Quercus arizonica) Yavapai County Native & Naturalized Plants, University of Arizona Cooperative Extension cals.arizona.edu/yavapaiplants/SpeciesDetail.php?genus=Quercus&species=arizonica Canyon Live Oak (Quercus chrysolepis) Yavapai County Native & Naturalized Plants, University of Arizona Cooperative Extension cals.arizona.edu/yavapaiplants/SpeciesDetail.php?genus=Quercus&species=chrysolepis Gambel Oak (Quercus gambelii) Yavapai County Native & Naturalized Plants, University of Arizona Cooperative Extension cals.arizona.edu/yavapaiplants/SpeciesDetail.php?genus=Quercus&species=gambelii Palmer Oak (Quercus palmeri) Yavapai County Native & Naturalized Plants, University of Arizona Cooperative Extension cals.arizona.edu/yavapaiplants/SpeciesDetail.php?genus=Quercus&species=palmeri Shrub Live Oak (Quercus turbinella) Yavapai County Native & Naturalized Plants, University of Arizona Cooperative Extension cals.arizona.edu/yavapaiplants/SpeciesDetail.php?genus=Quercus&species=turbinella  |