The primary objective is deterrence, but the chips also will aid in tracking down and identifying stolen saguaros. The largest theft at the park occurred last year, when 17 saguaros were dug up and stashed for transportation later. The culprits were caught, but there have been other cases where three to five plants have been taken at a time.

Saguaros are unique to the Sonoran Desert, 120,000 square miles covering portions of Arizona, California and the northern Mexican states of Baja California and Sonora.

They’re majestic giants that can grow to heights of 50 feet, sprout gaggles of arms and weigh several tons. They can take 50 years to flower and 70 years before sprouting an arm.A 2000 census of the two districts making up the Saguaro National Park outside Tucson estimated that there were 1.3 million saguaros there.

Plant pilferers typically target the relatively young and small specimens in the 4- to 7-foot range—which are probably 30 to 50 years old. Plants of that size typically fit in the bed of a pickup truck and can be covered with a tarp; bigger ones require heavy equipment to lift and larger vehicles to haul them. They typically can fetch $1,000 or more.

According to Bob Love, chief ranger at southern Arizona’s Saguaro National Park, the park wants the chipping program, but will have to go through a lengthy environmental compliance study to ensure the chips don’t harm the plants themselves or create air quality, soil or endangered species issues.

The microchips don’t emit a signal. Instead, each is uniquely encoded, and waving a special wand within about a foot powers the chip to send back its code. Love said it’s common to see trucks carrying cactus on roads that intersect the park. “So if we saw something like that, we could momentarily stop them and wave these wands over them,” he said.