Mojave National Preserve
Joshua Tree

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This spectacular plant has become the symbol of the Mojave Desert. Mormon pioneers named the species for the biblical figure Joshua, because the trees uplifted limbs reminded them of Joshua praying and pointing to the heavens. John Fremont, early explorer and promoter of the West, called it "the most repulsive tree in the vegetable kingdom." Today its large size and unusual characteristics make it an appealing and attractive component of the desert, and it is hard to watch an hour of television without seeing a Joshua tree on a commercial. Joshua trees grow best at elevations between 2,000 and 6,000 feet. They also prefer flat or gently sloping terrain, and are usually supplanted on steep hills within their range by blackbrush and other scrubs. The largest trees can be massive, over 32 feet high with a trunk circumference of 12 feet. They do not have growth rings like true trees, so determining their age can be difficult, but one biologist has estimated that a tree in Joshua Tree National Park is about 900 years old. There are two recognized sub species of Joshua trees, or Yucca brevifolia as they are known in the scientific community. In the western and southern Mojave Desert one finds Yucca brevifolia brevifolia. These are the largest trees, have relatively long leaves and they branch only after they have flowered. Look for them in Joshua Tree National Park, Yucca Valley, Palmdale and Saddleback Butte State Park. Yucca brevifolia jaegeriana is found in the eastern Mojave Desert. This species is smaller and tends to be denser, has smaller leaves and can branch before its first flowering. Excellent populations can be found within the Mojave National Preserve and near Dolan Springs, Arizona. The Joshua tree grove at Cima Dome, again in the Preserve, is considered one of the densest and largest in existence. Until the creation of Mojave National Preserve no population of Yucca brevifolia jaegeriana was protected. Germination is associated with abundant winter precipitation. Grazing animals from cows and deer down to small rodents usually eat the young Joshua sprouts, so most trees begin life in the protective canopy of a bush. After several years of growth the dagger like leaves provide protection, and eventually it grows up and out of the protector plant. Mature plants produce beautiful white flowers, and a good Joshua tree bloom is one of the delights of the desert. An interesting example of mutual dependence exists between yucca moths and Joshua trees. Like other yucca, Joshua trees are only pollinated by a specific species of yucca moth, so each are dependent on the other for survival.