If you travel from the alpine zone to the lowland tropics, more than just the climate will change. Species composition follows changing environments: there is a reason why a Cyathea tree fern doesn’t live in Colorado but does live in Costa Rica. (Note of course that many millions of years ago, when the earth was…

The sound of a rattlesnake is unmistakable once you’ve heard it once. But this sound wasn’t on my mind when I almost stepped on one a few weekends ago. I was in the Santa Rita mountains of southern Arizona. The highest peak, Mt. Wrightson, looms 7000 feet above the Tucson basin. In late March, mountaintops…