The largest species of yucca is the Joshua tree. It lives primarily in the Mojave Desert but can also be found in a small part of the Sonoran Desert, in the pine forest in the San Bernardino Mountains, and in a little corner of Utah. It grows at 2,000 to 6,000 feet.

Archaeological evidence dates the tree to the Pliocene epoch, more than 2 million years ago. Then, the climate was warm and moist and supported widespread groves of Joshua trees. I’ve heard tell that with global warming, our area will have warm, moist, humid weather like Hawaii. Maybe this will be enough to save some of the Joshua trees.

These evergreens can range from 15 to 40 feet tall when mature. They take up to 60 years to reach maturity, and they commonly live up to 150 years. The oldest tree on record was estimated to be 1,000 years old. It was 80 feet tall. Their growth rate is slow, estimated at one-half to 2-1/2 inches per year.

It is not a true tree. It does not produce annual tree rings, so it is difficult to tell the exact age of the plant. The best guess is to measure the height and divide it by the probable growth rate.

This plant was useful to indigenous peoples. Leaves were woven into baskets and made into sandals and cordage, and the flowers, buds and seeds were eaten. Later, the wood was used as a source of fuel for steam engines and fence posts.

The protracted drought is killing the Joshua trees.

Although the plant likes dry, sandy soil, the trees are overly stressed due to our 20-year drought. In fact, entire groves of Joshua trees are dying out.

Joshua trees depend upon perfect conditions. They like spring rains and a winter freeze. They have been barely surviving without either condition being met in many areas. Many groves are weak and dying.

The Joshua tree is one of the indicator species that is expected to have a range reduction and shift with climate change. Conservationists are concerned there could be up to a 90-percent loss of their current range by the end of this century.

Thirteen thousand years ago, when the plant faced climate change and range reduction, the giant sloth ate the leaves and seed pod, effectively moving the seeds from one place to another and establishing new groves. Today, we don’t have the sloth to move those seeds around. No other animal eats the seeds and transports them.

The Joshua tree is important to the desert ecosystem. Birds such as the Scott’s oriole can be found nesting in the branches, wood rats nesting below and using the spiny leaves for protection, night lizards and rattlesnakes living in a pile of dead branches.

The Joshua tree propagates by the root and seeds, as well. If the tree is downed by fire or flood, the root will send up new shoots. Seeds require germination by the yucca moth. The yucca moth pollinates the flowers and lays her eggs at the same time. The larvae hatch and eat some of the seeds, so the moth and the Joshua tree are dependent upon one another for survival.

The next time you drive up Interstate 5, keep your eyes peeled for a small stand of Joshua trees. A few years ago, this was a thriving grove. Now, there are only a few alive. We may be witnessing the beginning of the end of the Joshua tree.

Dianne Erskine-Hellrigel is executive director of the Community Hiking Club and president of the Santa Clara River Watershed Conservancy. If you’d like to be part of the solution, join the Community Hiking Club’s Stewardship Committee. Contact Dianne through communityhikingclub.org or at zuliebear@aol.com.