   Respect the Mesquite Tree - January 24, 2007 Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Mesquite trees are often removed from residential areas without consideration of their many virtues. Sure, they are spiny and often shrubby in form, but they also require little or no irrigation, provide food and cover for wildlife, attract bees and other interesting insects, and provide nesting sites and habitat for migratory songbirds. In other words, they have value that extends far beyond being a charcoal source for your backyard barbeque. Velvet mesquite (Prosopis velutina) is the predominant species found in the Verde Valley. It grows as a tree on the floodplains and terraces near the Verde River and becomes shrubbier where it is found on slopes and rocky areas. Mesquite has the ability extract water from deep within the soil and where it grows near rivers and streams, it can also have a two-tiered root system: one shallow and one deeper (near groundwater). In Yavapai County, they are rarely seen above the 5,000 feet elevation level. Mesquite bosques (Spanish for “forests”) once lined the Verde River on the remnant floodplain terraces. Some remnant bosques are still present along the Verde and in these areas, mesquites trees can be up to 30 feet tall. Alteration of riparian areas and development has greatly decreased the number and overall acreage of mesquite bosques across Arizona. In some areas where mesquite bosques have been removed, invasive species such as saltcedar and Russian olive have replaced them. Mesquites are also legumes (relatives of beans and peas) which have the ability to “fix” atmospheric nitrogen increasing nitrogen available in the soil. Here, legume roots become associated with beneficial soil bacteria (Rhizobium sp.) which have the ability to convert nitrogen gas to a form that plants can use. They fertilize themselves and neighboring plants through this symbiotic process. This process is also utilized by many gardeners when they plant nitrogen fixing cover crops to enrich garden soil. Clusters of fragrant yellow mesquite flowers bloom in the spring. Honeybees are often brought into mesquite stands to make flavorful honey. The flowers develop into seedpods and ripened seeds become hard shelled beans. These beans are valuable wildlife and livestock forage. The mature beans can be ground into sweet flour called “pinole”. I’ve tried it and it tastes pretty good. Other Arizona native mesquites are honey mesquite (Prosopis glandulosa) and screwbean mesquite (Prosopis pubescens). Both species are found at lower elevations than velvet mesquite, but are suitable for planting below 4,000 feet elevation and would be an excellent choice for drought tolerant landscaping. Honey mesquite is popular in the nursery trade as it becomes an attractive, almost stately, tree. Screwbean mesquite has a twisted branching habit and an attractive, twisted seedpod. These are less common in nurseries. Avoid the Chilean mesquite hybrids as they will not tolerate our winter temperatures and tend to fall over in maturity. Urban legends sometimes say that mesquites harbor Texas root rot (Phymatotrichum omnivorum) also called cotton root rot. Texas root rot is a disease that is present in some areas of the Verde Valley and it can infect a broad range of host plants. Mesquite trees tend to tolerate the presence of Texas root rot. This does not mean that it harbors the disease, but since it is somewhat tolerant, the disease could be present and have little or no effect on the mesquite. When a more susceptible host is planted in these areas, it could succumb to the disease while mesquites continue to survive. Fruit and nut trees, roses, sycamore, cottonwood, ash, oleander, xylosma, and many other species are susceptible to Texas root rot. So, I hope this column encourages readers to better appreciate mesquite trees. They are an excellent choice for drought tolerant landscaping, compatible with birds and wildlife, and have a lot of character. 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 cottonwoodmg@yahoo.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://cals.arizona.edu/yavapai/anr/hort/byg/. |