Joshua trees are native only to the American Southwest and mostly found in the Mojave Desert, which spans across a vast section of southern California and southwest Nevada. However, some trees grow in other areas of the Southwest in the Sonoran Desert in Arizona and even in the San Bernardino Mountains. Their prickly evergreen leaves grow in clusters at the ends of their thick branches giving them an appearance that can’t be missed and they are best seen at none other than Joshua Tree National Park.
Early Native Americans took advantage of Joshua trees by utilizing its tough leaves to produce baskets and sandals while also relying on its flower buds and seeds for their diet. Ranchers and miners who later arrived in the area also made use of the Joshua tree in a number of different fashions. The ranchers actually used the limbs and trunks for fencing and corral while miners used them for a source of fuel for steam engines utilized in ore processing.
The name “Joshua tree” is believed to have derived from the times when Mormon settlers first crossed the Colorado River and encountered these unique trees in the mid 1800s. To them, the leaves resembled hands stretched out in supplication like the biblical figure, Joshua, and thus the name stuck.
Joshua trees, known as Yucca brevifolia, aren’t really even trees but are a type of yucca and belong to the agave family. These beautiful trees can live for hundreds of years, though some scientists think they might be capable of reaching up to 1,000 years in age. Their ages, however long, are difficult to ascertain because they don’t grow rings. The best way to estimate their age is to judge by their height but even that can be problematic because these trees grow between 1/2 an inch and 3 inches a year. Some of these trees can sprout quite high for yucca, with one in Joshua Tree National Park reaching as high as 40 feet.
The root system of the Joshua tree is fascinating. They grow both deep and shallow roots. The shallow roots only grow a couple of feet underneath the soil but the deeper roots sometimes extend to depths of 30 feet. These deep roots grow large bulbs, which serve to store water and can be up to four feet in circumference and weigh up to 40 pounds!
Joshua trees rely exclusively on yucca moths for pollination. These moths lay eggs in the flowers of the trees and deliberately pollinate the Joshua trees so that when the eggs hatch, the caterpillars will have seeds to eat. It may seem like the Joshua tree is getting the short end of the stick in this deal but actually it produces so many seeds that there’s usually surplus left over so that both parties to this relationship end up better off.
Even more fascinating, scientists have discovered certain species of yucca moths pollinate only certain varieties of Joshua trees, creating even more incredible evidence of one of best examples of coevolution in the world. Charles Darwin at one time remarked that the relationship between the Joshua tree and the yucca moth was “the most remarkable fertilization system ever described.”
Besides moths, many other animals depend on the Joshua tree. Scott’s orioles are known to nest in the branches of the Joshua tree and wood rats are known to build nests in the base of the yucca, sometimes placing the spiny leaves of the tree in there for protection of the nest. And even when these trees fall over they create rich ecosystems full of insect-dwellers, which small reptiles feed on.
Unfortunately the future is bleak for these trees as a recent study in 2011 predicted that 90% of Joshua trees will be eliminated in the next sixty to ninety years as a result of climate change. Thousands of years ago, Joshua trees were able to survive rising temperatures because their seeds were widely dispersed by large mammals like the now-extinct Shasta ground sloth. However, today only small rodents like squirrels disperse their seeds but not far enough for the trees to migrate into more suitable climate zones. Thus, with rising temperatures, the Joshua tree population will likely suffer a drastic decline in the near future.