EARLIER THIS YEAR, A DOZEN volunteers and staff armed with trowels kicked off an urgent experiment in cactus conservation. On a clear March morning they spread out within the high-quality habitat of the Tucson Audubon’s Mason Center, pushing wheelbarrows loaded with three-to six-inch cacti. By noon, they had planted 130 saguaros near ironwood, mesquite, and palo verde “nurse trees,” which provide shade and boost the baby cacti’s chances of survival.
If the succulents take root, they have a long way to grow. They won’t start flowering until they are 35 to 70 years old, and
