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22 City Trees State Coordinators Managing Urban Forests in Arizona: Diversity, Challenges, and Reward by Alix Rogstad, Urban and Community Forestry Program Manager, Arizona Department of Forestry and Fire Management Partner Update Arizona is a land of extraordinary environmental diversity created by its unique land formations and climate. With five dis- tinct biogeographic regions, the State's nearly 114,000 square miles (295,259 sq km) of land offer some remarkable con- trasts: (1) the desert shrubs, juniper woodlands, and montane forests of the Colorado plateau; (2) the conifer woodland and grassland communities of the Mojave Desert; (3) the rugged montane forests, oak woodlands, and grasslands of the Central Highlands (Mogollon Rim); (4) the Sierra-Madrean evergreen woodlands and lush riparian woodland communities of the Sky Islands; and (5) the Arizona uplands and desertscrub commu- nities of the Sonoran Desert. The edges of a particular biotic community are determined by precipitation (as rainfall and/ or snow) and temperature, so the actual boundaries are often tenuous and are influenced by local elevation, slope exposure, fire frequency, and soil. Within the five biogeographic regions of the state, there are thirteen biotic communities that make Arizona the third most biologically diverse state in the country (NatureServe, 2002; http://www.natureserve.org/library/stateofunions.pdf): • Alpine Tundra – found above 11,500 ft (3505 m) elevation; harbors limited plant growth because of the harsh condi- tions • Subalpine Spruce-Fir Forest – located at high eleva- tions (10,000-11,500 ft/3048-3505 m); dominated by Englemann spruce (Picea engelmannii), corkbark fir (Abies lasiocarpa) and quaking aspen (Populus tremuloides) • Montane Mixed-Conifer Forest – occurring from about 8,000-10,000 ft (2438-3048 m) elevation; supports a good mix of Douglas-fir (Pseudotsuga menziesii), white fir (A. concolor), ponderosa pine (Pinus ponderosa) and southwestern white pine (P. strobiformis) • Montane Ponderosa Pine Forest – typically 6,000-8,000 ft (1828-2438 m) elevation; often essentially pure stands of ponderosa pine with Gambel oak (Quercus gambelii) being the most important associate species • Pinyon Pine-Juniper Woodland – found between 5,000- 7,000 ft (1524-2134 m) elevation; although dominated by pinyon pine (P. edulis) and several juniper species, this plant community also supports many shrubs and grasses • Sierra-Madrean Evergreen Woodland – originating in the Sierra Madre mountain range of Mexico, this plant com- munity type reaches its northern extent in southeastern Arizona; evergreen oaks dominate (Emory oak (Q. emoryi), Mexican blue oak (Q. oblongifolia), and silverleaf oak (Q. hypoleucoides)) and other drought-tolerant species like alligator juniper (Juniperus deppeana) and pinyon pine are common • Chaparral – found from 4,000-6,000 ft (1219-1828 m) elevation primarily along the Mogollon Rim in central Arizona; supports a mix of shrub species (mountain mahogany (Cercocarpus montanus), shrub live oak (Q. turbinella), and manzanita (Arctostaphylos manzanita)) • Grasslands – found throughout Arizona typically above 3,500 ft (1067 m) elevation; three types of grasslands occur in Arizona (Great Basin, Plains, and semidesert grasslands), all of which support grasses mixed with suc- culents and other small desert trees like honey mesquite (Prosopis glandulosa) • Great Basin Desertscrub – found mostly in the northeastern portion of the state between 4,000-6,500 ft (1219-1981 m) elevation; dominated by scattered low shrubs like sage- brush (Artemisia tridentata), greasewood (Sarcobatus ver- miculatus), and rubber rabbitbrush (Ericameria nauseosa) • Sonoran Desertscrub – typically below 3,500 ft (1067 m) elevation and found mostly in the southern half of Arizona; due to a bimodal rainfall pattern, large cacti (saguaro and organ pipe; Carnegiea gigantea and Stenocereus thurberi) flourish alongside trees like ironwood (Olneya tesota), velvet mesquite (P. velutina), and blue palo verde (Parkinsonia florida) • Chihuahuan Desertscrub – located in the southeastern portion of the state between 3,500-5,000 ft (1067-1524 m) elevation; known for its vast grassland valleys that also host shrubs like honey mesquite, yucca (Yucca spp.), and Parry's agave (Agave parryi) • Mojave Desertscrub – located between 3,000-5,000 ft (914-1524 m) elevation and in the northwestern corner of Arizona; the severely hot and dry climate results in a rela- tively barren landscape with scattered shrubs like creosote bush (Larrea tridentata), yucca, and Joshua trees (Yucca brevifolia) • Riparian Woodland – occurring throughout the state at different elevations; typical trees include the cottonwood (Populus fremontii), willow (Salix spp.), and box-elder (Acer negundo) in the higher elevations, and Arizona walnut (Juglans major), sycamore (Platanus wrightii) and velvet ash (Fraxinus velutina) in lower elevations