Christian Science Monitor: With a scruffy, desert floor extending as far as the eye can see in all directions – dotted with the Mojave Desert’s signature spiky, gnarled Joshua trees – veteran park ranger Joe Zarki kneels down in the dust. Pointing to an invasive, red brome grass, which has proliferated here in the past few years, he explains why the rise in temperatures that have helped it thrive could signal the end of Joshua trees within a century. “These exotic grasses dry out, which means that the fires we …