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Thirty years ago, Philippa Drennan joined her colleague John Waggoner in a study of Joshua trees in the Mojave Desert. His initial research that concerned the distribution of Joshua trees within a range of altitudes in the remote desert became long-term monitoring of new growth and flowering of specific trees. Changes in climate and environment have affected the trees, and Drennan describes here what they have observed through their research in the Mojave National Preserve.

The Joshua trees of the Mojave Desert would not exist without the help of a single kind of tiny moth, and vice versa.

These two species, one that lives for hundreds of years, the other for only a few weeks as adults, are linked together biologically. Yucca brevifolia, the scientific name for the Joshua tree, must have its flowers pollinated by the yucca moth, Tegeticula synthetica, and no other. The moth pollinates only Joshua trees and is dependent on the seeds of the tree to feed its larvae. If either species should become extinct, particularly over a short period of time — in scientific terms, a few hundred years — the chances are that the other one will also cease to exist.

Mojave Slideshow