A New View of Saguaros.

Ray Turner aims his camera with great care at a precise spot on a nearby ridge at Saguaro National Park, east of Tucson, Arizona. First, Turner makes sure that two large saguaros--one with four armlike branches reaching out and up, candelabra-style, and the other just a column with no branches yet--are aligned with the same Santa Catalina mountain peaks in the background in exactly the same position as in previous pictures. Then, carefully, Turner checks his position and camera direction with his compass and global positioning system. Finally, he snaps several pictures of the saguaros and their surroundings, just as he has done periodically since 1962. We have photos from our study sites going as far back as 1867," says Turner, a retired US Geological Survey (USGS) botanist and perhaps the foremost authority on saguaros. He pulls out a 1984 photograph of the same site that shows four large saguaros. Today, only the two remain. The 1984 photo also shows several palo verde trees that are now gone. In their place, prickly pear cacti glisten in the early morning sun. "These photos show how the desert changes over the years," Turner says. "These sites are important for long-term research. They are among the oldest continually monitored plots in the world." Turner's research and that of others has helped shed new light on saguaros and other columnar cacti, recording changes in their numbers over time and illuminating their relationship with other plants and animals. At the same time, their studies demonstrate how much scientists still have to learn about what is certainly the Sonoran Desert's most-studied plant--and its most recognizable one. Saguaros are the largest cacti in the United States.