Ironwood is one of the largest and longest-lived Sonoran Desert plants, reaching 45 feet in height and persisting as long as 1,500 years.
It is a single or multi-trunked evergreen tree, and displays lavender to pink flowers in May. By early summer, the pods mature. Each 2-inch pod contains one to four shiny brown seeds that are relished by many Sonoran animals, from small mammals and birds to humans. Its iron-like wood is renowned as one of the world's densest woods.
The shaded sanctuary and richer soils created by ironwoods increase plant diversity and provide benefits to wildlife. Ironwoods are too hard to provide nesting cavities for birds, but the cacti that grow beneath them provide such opportunities. Insects abound within the ironwood complex, attracting birds and reptiles. As with other legumes, the ironwood's leaf litter supplies nitrogen to the soil and its seeds provide a protein-rich resource for doves, quail, coyotes, and many small rodents.
The Ironwood tree is found only in the Sonoran Desert, in the dry locales below 2,500 feet, where freezing temperatures are uncommon. In fact the Ironwood's habitat is almost an exact match of the Sonoran Desert boundry. Ironwoods are most common in dry ephemeral washes. Ironwoods function as oases of fertile and sheltered habitat within a harsh and challenging desert landscape. As a tree becomes established, it tempers the physical environment beneath it, creating a micro-habitat with less direct sunlight, lower surface temperatures, more organic matter, higher water availability, and protection from herbivores. Because of these factors, the Ironwood tree has immense ecological value in the Sonoran Desert.
Ironwood grows taller than most trees in Sonoran desert scrub, so it serves as a great perch and roost for hawks and owls. It's dense canopy is utilized by nearly 150 bird species. Add tall ironwoods to the scrubby vegetation on some desert bajadas, and you're likely to add 63 percent more birds than creosote, cactus and bursage alone could support. The ironwood's canopies are so dense that they reduce the probability of extreme heat exposure in the summer.
Air temperatures may be 15 degrees cooler under ironwoods than in the open desert sun five feet away. Ironwood also shelters frost sensitive young saguaros, organ pipe cactus, night-blooming cereus and many other native plants growing beneath them. More than 230 plant species have been recorded starting their growth within the protective microclimate under ironwood "nurse plants." This also creates an optimum wildflower nursery which is foraged by rabbits, bighorn, and other native species.
In addition to the birds, there are 62 reptiles and amphibians, and 64 mammals that use ironwoods for forage, cover and birthing grounds. At just one site in the Silverbell Mountains, an ironwood-bursage habitat also shelters some 188 kinds of bees, 25 ant colonies, and 25 other types of insects. That adds up to an extraordinary level of biodiversity.
Ironwood flowers are pollinated by native bees and used as medicine. The leaves are foraged by bighorn sheep, pronghorn antelope and mule deer. The leaf litter provides nitrogen and organic matter for soil enrichment in which symbiotic bacteria and fungi create "islands of fertility". The seeds are eaten by native doves, quail, and rodents and can be leached and ground for use as food for humans.
"By keeping ancient ironwoods alive, we maintain the oldest medicine show, native wildlife menagerie and migratory pollinator bed-and-breakfast in town. These hardy old trees provide ideal habitat for everything from night-blooming cacti to tree lizards, desert bighorn and cactus owls. The list of residents living under a 45-foot ironwood reads like the Who's Who of the Sonoran Desert."
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