Mesquite trees belong in Arizona. As Jay Sharp, editor and author for the website DesertUSA.com, expresses, "the mesquites symbolize our Southwestern deserts" as much as "the Coyote, the Black-tail Jackrabbit, the Western Diamondback, scorpions, the Saguaro and prickly pear cacti." Indeed, mesquite trees in Arizona are "as blended into the life of the land as cornbread and tortillas." (Lometa)
Perfectly Adapted to the Desert
Mesquites are very hardy desert trees, having adapted over the centuries to life in the desert landscapes in and around Arizona. All of their physical characteristics ensure their survival here, including their foliage, their bean pods, and their root systems. They grow well in full sun and high temperatures, but will also tolerate the cold during Arizona's winter (down to 0º Fahrenheit). They are sometimes found in rather high elevation and will adapt to shallow rocky soils. According to reports by the U. S. Department of Agriculture and Forest Service, a mesquite tree can live for more than two centuries. (Sharp)
Mesquite trees in Arizona can survive in areas that receive very little rainfall because of their expansive root system. The lateral roots of a mesquite tree reach out many times farther than its canopy. They also have very deep tap roots that can dig for a drink as deep as 175 feet below ground level, though a depth of 50 feet is more typical. So, they simultaneously have access to water both at the very top and bottom layers of the soil.
The tiny waxy leaflets of mesquite trees retain precious moisture by minimizing the moisture lost through transpiration. They are deciduous trees, meaning they offer excellent shade during the summer but drop their leaves and allow the sunshine through during the winter for warmth. During extreme drought, they will diminish transpiration even further by prematurely dropping their leaves.
The mesquite tree is a member of the legume family (relatives of beans and peas), which makes it especially adapted to an arid environment. Mesquite trees have the ability to fertilize themselves and surrounding plants through a symbiotic relationship with colonies of soil bacteria. The bacteria that inhabit mesquite tree roots convert or "fix" atmospheric nitrogen, making available in the soil this mineral that is essential for the growth and germination of plants. Many gardeners utilize this same process to enrich soil by planting nitrogen fixing cover crops. (Sharp, Schalau)
Mesquite trees in Arizona are amazingly prolific. Their beans, encased in protective pods, are very durable. In fact, "A seed left undisturbed in its pod can stay viable for up to 40 years." (Clayton) Animals play an important role in the scarification of the seeds (needed for germination) and dispersal through fecal matter.
Appearance
Mesquite trees are easy to identify, looking almost like a giant fern bush. They can reach a height of 30 feet, but the average mesquite tree growing wild in the Arizona desert is about half that size. Many have multiple trunks. Under the harshest of conditions, the mesquite will resemble a bush more than a tree. Their branch structure is often very twisted and jointed, adding to their individual uniqueness. In the spring and early summer, they display clusters of finger-shaped protuberances covered in tiny delicate flowers. These are followed by the formation of the long, thin bean pods, which are usually a shade of brown but vary in appearance between species. Many types of mesquite trees have thorns of some kind, which can either be very short or monstrous in length (and all are horribly sharp!).
Three Arizona Mesquite Tree Natives & Their Cousins
There are about 40 mesquite varieties found worldwide, but three species are native to the state of Arizona. They grow not only in the Sonoran desert, but also in the Mojave and Chihuahuan deserts. Their range is astonishing, spanning tens of millions or acres from western Texas to California, from Mexico to southern parts of Utah. They can thrive in a great diversity of habitats as found within the range described. (Lometa, Sharp)
The three mesquite tree species native to Arizona are:
Prosopis glandulosa - known as the honey mesquite or Texas Mesquite. These usually have a weeping form, and can be quite pretty.
Prosopis velutina - known as the Arizona mesquite or native mesquite. Also called the velvet mesquite because of the soft hairs that cover young growth. They are rather shaggy and snarled in appearance. They are popular in nurseries, and will grow well on lawns and golf courses.
Prosopis pubescens - known as the screwbean mesquite, earning its name from the spiraled or coiled shape of their seed pods.
Besides these three, there are many other types of mesquite trees that grow in Arizona. Many are hybrids of the honey, velvet or screwbean mesquite, occurring mostly where the respective ranges of these native species overlap. Others are nonnative mesquite species, most originating from South America. There is the Argentine mesquite (Prosopis alba), the Chilean mesquite (Prosopis chilensis), and numerous other varieties and their hybrids. No nonnative species will be as suited to the climate here as the mesquites that are native to Arizona. For example, the Chilean mesquite does not seem as tolerant of the lower winter temperatures in Arizona.
Botanical Foes
Despite their many positive qualities, mesquite trees are considered by many as an invasive weed. In many countries outside of North and South America where they have been introduced they have been extremely invasive and troublesome, especially in Australia.
The mesquite tree is cursed by inhabitants of our own Arizona desert as well. Cattlemen especially dislike them, but the overgrazing of their herds over the past couple of centuries has exacerbated the very problem that they complain about, which is the mesquite tree's competition with grasses. In an area that is overgrazed, cattle not only threaten the populations of the natural grasses that compete with mesquite trees for water, but they also help the mesquites spread by eating and dispersing the seeds. As Frank Dobie puts it, "The white man sowed with over-grazing; he is now reaping thickets of mesquites that are stabbing millions of acres of land into non-productiveness." All efforts to thwart or control this stubborn native Arizona tree have all failed and been deemed impractical or ineffective. Whether by fire, herbicide use, or physical tree removal of various means, the costs and environmental side effects of trying to control the population and spread of the mesquite have made it a problem with no easy solution.
Sharp reminds us: "Uninvited guest or welcome neighbor, the mesquites belong to the desert. They evolved in the desert. They play a core role in the desert ecosystem." (Jay Sharp)
Historic Significance and Modern Uses
"Over the past several centuries, no one plant has probably played a greater and more vital role in the lives of humankind in the southwestern United States than the short stature, crooked mesquite." (excerpted from The Magnificent Mesquite by Ken E. Rogers.) Indeed, the mesquite trees strewn across the Southwest have literally saved numerous lives. They provided the "manna from heaven" for the suffering men of the 1841 Texas Santa Fe Expedition, as recorded in the journal of George W. Kendall (also quoted by Rogers). The beans are sweet and nutritious, and more protein-rich than the soybean. (Lometa)
Another food that comes from the mesquite trees in Arizona (though not directly) is honey. The swarms of bees that are strongly attracted to the mesquite flower's nectar do more than just fill their important role as pollinators, after all. This, however, does not complete the list of foods derived from the mesquite. Even their sap has been utilized as sweet gum or as black dye.
'Pinole' is made by grinding the pods, with or without the beans still inside. It can be used as four or, because of its sweetness, as a condiment or spice. This mesquite flour is said to be healthy for diabetics, because it is sweetened by fructose, which the body processes without insulin. This is just one example of the many digestive and nutritional advantages of the mesquite tree and other foods of the desert that has been discovered. (Lometa)
Various parts of the mesquite tree have also been used as remedies for many different ailments by the Indians and settlers of the frontier era. Examples of the ailments that the mesquite tree helped to ease or heal are: diarrhea, dysentery, colic, flesh wounds, headaches, ailing eyes, and sore throat.
The wood, bark and pods of mesquite trees are popularly used for barbecue and for other purposes. The dry wood burns slow, hot and with very little smoke. It has an unmistakable aroma. Some insist that burning the pods along with the charcoal and wood chips make the flavor even richer. (Lometa) Besides for heat and for cooking, the wood has been used for the construction of Spanish missions, colonial haciendas, ranch houses and fencing. (Sharp) The Native Americans used the hard mesquite wood for spears and arrowheads, and the bark of the mesquite tree for making baskets and fabrics. The thorns were used as needles. Today the wood is artistically valuable for making furniture or sculpture because of its sometimes dark colors and beautiful gnarled patterns.
Of course, mesquite trees in Arizona are beneficial not only to humans but also to our wildlife. Animals use the mesquite as shelter, habitat and food. In the late summer and fall, mesquite beans make up as much as 80 percent of the coyote's diet! The bean pods also can serve as fodder for livestock when the grasses are inadequate.
Maintenance, Problems and Treatments
Though mesquite trees in Arizona do not require much maintenance, the specimens growing around our homes could benefit from a little extra care during unusually hot summers or times of extended drought. Sun-scorch is one of the very few problems that can plague mesquite trees planted as part of landscaping, though they are not as susceptible to this as are citrus and other fruit trees in Arizona. Infrequent but deep watering and occasional fertilizing will help ensure that the mesquites around our homes do not suffer a decline of health and beauty.
During years when Arizona receives plentiful rainfall, mesquite trees do not need extra watering. However, in times of drought, the leaves will become sparse and allow more sunlight through to the branches. This is exacerbated by the need in the city to keep mesquite trees thinned out to survive storms and heavy winds, so as not to cause damage to homes and other structures. If the bark is exposed to too much intense sun, sun-scorch may occur, especially where the sunlight is most direct (i.e. on the top of horizontal branches at midday). Sun-scorch causes permanent damage to the cambium, or the sapwood layer underneath the bark. The cracked bark and dead tissues resulting from severe sun-scorch can lead to secondary infections and infestations, such as bark beetles and a fungus called 'sooty canker'.
Sun-scorch on mesquite trees in Arizona can be prevented but not undone. Reflective paint on the most vulnerable branches will minimize a mesquite tree's chances of being sun-damaged. Branches already affected should be removed back to a branch with healthy tissues. The best way to prevent sun-scorch is to encourage leafy growth to protect the tree during the hotter part of the year by some watering and by light fertilizing. Give the mesquite trees ammonium sulfate once in the springtime. Unless already fed by drippers or sprinklers (whether in your own or in a neighboring yard), water them deeply every two months from early spring to early fall. If the monsoons bring adequate water, skip deep-watering during this period.
A mesquite tree that is planted in someone's yard may not be as hardy as the volunteer trees growing wild in the desert. Most likely, a nursery-grown mesquite tree planted for landscaping purposes has spent some time in a pot. The more time any tree spends in a pot, the more likely it is to become root-bound. An impaired root system makes for a mesquite tree that not only struggles to receive what little water they need to thrive, but also is more prone to falling over because their 'anchoring' is not as sturdy. John Begeman says, "Try as you may, it is impossible to get a wobbly tree to anchor in the ground. By putting up stronger stakes and wires, righting the tree when it falls over, [...] you are just prolonging the inevitable. [...] The best thing to do with an unstable tree is to get rid of it and start over with a healthy specimen." Please refer to his article entitled Remove Wobbly Mesquite Trees [http://ag.arizona.edu/gardening/news/articles/17.29.html] for more information on the subject.
If nothing else, I hope that this article on mesquite trees in Arizona increases some Arizonans' appreciation for this native plant as something that undeniably belongs in this desert we call home.
"Primroses burn their yellow fires
Where grass and roadway meet;
Feathered and tasseled like a queen,
Is every old mesquite."
-J. Frank Dobie
BIBLIOGRAPHY
Begeman, John. "Remove Wobbly Mesquite Trees." Arid-Southwestern Gardening Information. Sep 2003.
Begeman, John. "Sun-Scorched Mesquite and Palo Verde." Arid-Southwestern Gardening Information. Mar 2000.
Clayton, Robin N. "Velvet Mesquite Tree." Arizona Highways.
Dobie, Frank J. "The Mesquite." Arizona Highways. Nov 1941.
Lometa. "Mesquite (Thing)." Everything2. Aug 2002.
Shalau, Jeff. "Respect the Mesquite Tree." Backyard Gardener. Jan 2007.
Sharp, Jay W. "The Mesquite: Something that Belongs." DesertUSA.
