"Hot" is the first adjective that comes to mind when people think of the desert. The desert's scorching heat can become unbearable for wildlife and humans alike. Fortunately, the deserts of the Southwest yield several species of trees that provide shade and shelter beneficial to both wildlife and humans. These trees can also add form and beauty in any desert landscape.
Yucca brevifolia, commonly called the Joshua tree, is a large, erect, evergreen, arborescent monocot (having single-leaf seeds). The Joshua tree is endemic to the Mojave Desert, which covers southern California, Mexico and western Arizona eastward into southern Nevada and southwestern Utah. So named because it reminded Mormons of the biblical character Joshua with arms aloft and waving, the Joshua tree can reach heights of 16 to 49 feet. The huge, reddish-brown to gray trunks can grow to 2 to 4 feet in diameter. The branches are erect, ascending or spreading, and form a dense, compact, rounded top.
A series of green pods that usually have 7 to 9 buds on each new branchlet in grouped clusters appears in early spring, covering the stalk or branch. The flower ripens to light cream- or ivory-colored waxy blossoms that emit an unpleasant, mushroom-like odor. The Joshua tree produces inflorescence (group of flowers) once or twice each year, but rarely on the same branch. Fruit first develops near the base of the inflorescence while the upper part is still in flower. Annual fruit production varies greatly under natural conditions, usually during wetter years.
Prosopis chilensis, commonly called Chilean Mesquite, is a thornless, rapid-growing tree that has an upright appearance and twisted, dark, coarse textured bark. Chilean Mesquite can grow up to 30 feet tall with up to a 30-foot spread. Known to double its size within a year, Chilean Mesquite requires ample space to develop properly. This tree has foliage that is open, ferny and evergreen. In late spring, Chilean Mesquite produces yellow-green, unremarkable, catkin-like flowers. By early summer clusters of curvy, brown seed pods appear.
Chilean Mesquite will tolerate an array of soil types and growing conditions. Once established, the root system is somewhat invasive. Planting as far away as possible from the house's foundation and swimming pool will prevent these roots from causing damages.
Two species of Palo Verde are common in the Southwest--- Yellow (Cercidium microphyllum) and Blue (Cercidium floridum) Palo Verde. Yellow Palo Verde, also commonly known as Foothill Palo Verde, has yellow-green bark and abundant light yellow flowers that bloom in April or May. Yellow Palo Verde grows up to 15 feet tall and 20 feet wide. The Blue Palo Verde, which is Arizona's state tree, has bright green or blue-green bark. Growing up to 20 feet tall and 25 feet wide, the Blue Palo Verde produces tiny leaves and yellow flowers in late March or April.
Aside from providing shade, both Palo Verdes provide nest sites and insect prey for birds. The seeds become an important food source for quail, doves, javelina, ground squirrels and many other desert rodents from late spring to summer. Rabbits, deer and bighorn sheep browse the Palo Verde's twigs.