Measuring Arizona - desert state with 58 champion trees

American Forests, Spring, 1998 by Craig Noble

MOVE OVER, FLORIDA. NOW THE DESERT STATE CAN BOAST CANYONS. CACTI - AND MORE NEW CHAMPION TREES THAN ANYONE ELSE.

Arizona

Where mineral mountains crisscross basins bare of green. Where rattlesnakes, scorpions, and gila monsters seek shelter from the sun, and the law of the land is to ration water. A land far removed from the towering big tree groves of the Sierra Nevada and the wet slopes of the Pacific Northwest.

Given that, it may surprise you that Arizona claims 58 crowns in the 1998-99 National Register of Big Trees. Thirty are new or reinstated champs, giving Arizona top status for new listings and bumping Florida, which previously held that title. What is it about the desert state that gives it this distinction?

Ironically, the same geography, topography, and climate that make Arizona such a challenging habitat to live in also are responsible for its multitude of champions. The southwestern third of the state shares the Sonoran Desert with California and Mexico. The Sonoran is one of the Southwest's three great deserts but an unusual one because it has two rainy seasons. Rainy, of course, is a relative term here since annual precipitation averages less than 10 inches. It's also subtropical. Species have evolved here that live nowhere else.

"We've got probably 118 species of native trees," says Robert Zahner, coordinator of the Arizona Register of Big Trees. "Approximately half of those are endemic to the desert Southwest, which means they occur only in southwest New Mexico, southern Arizona, and southeast California, and also, of course, in Sonora, Mexico." Nineteen species are endemic to Arizona, which means their national champions must be in Arizona, he says.

A retired forestry professor, Zahner has been hiking the state's backcountry mountains and deserts for 25 years. When he first came to Arizona, he made it his hobby to learn all the plant species, especially the trees.

It's an avocation he shares with his wife, Glenda, and together they have discovered 16 national champions. In some cases the task was relatively easy. The Ajo oak (Quercus turbinella var. ajoensis) occurs only in the Ajo Mountains in Organ Pipe Cactus National Monument on the Mexican border, and there is only one known grove in the entire world.

Harder to find was the elephant-tree (Bursera microphylla), whose gray-white bark and odd-shaped branches give it an elephant-like appearance. The tree grows 40 or 50 feet high in parts of Mexico, but the specimens in this country rarely qualify as trees. Sensitive to cold, they are killed back to shrub size by the occasional frost that settles every three to five years on even the warmest spots in Arizona. Undiscovered in the U.S. until 1910, the elephant-tree was included in the list of species without champs in the 1996-97 National Register.

That challenge spurred Zahner's friend and fellow big tree hunter Ken Morrow to spend two days searching for a qualifier. He found it after following a jeep track 95 miles through the Cabeza Prieta Wildlife Refuge and into the Tinajas Altas Mountains of Yuma County.

"I walked up a rocky drainage of a canyon and sure enough among these big boulders on the hillside there looked to be a number of big elephant-trees," Morrow says. "We were just looking for something over 12 feet so that it would be eligible. There was one that was 12 feet tall with a few main trunks. This one had six or eight main stems. We added up the points [and] it wasn't real impressive, but it was a start."

As is the case with many desert species, neither the 31-point elephant-tree nor the 127-point Ajo oak is very large. But not all Arizona's titleholders are little big trees. Consider the champion Fremont cottonwood (Populus fremontii var. fremontii) in Santa Cruz County. With a circumference of 42 feet, Zahner says it has by far the biggest trunk he's seen on a nonconiferous tree. Weighing in at 623 points, it's a big tree by any standards and, in fact, may be the largest cottonwood in the world.

Arizona's cottonwood was the official national champ from 1970 until 1986, when a specimen with more points was nominated in New Mexico. No one could remember the Arizona tree's exact location to remeasure it, so the New Mexico tree reigned until 1995, when a big tree hunter from Iowa called Zahner to say he thought he'd found it. Arizona's contender had grown significantly since its last measurement in 1970 and took back its tide in this edition of the Register.

"It really was the champion all along, but since it was not periodically remeasured, we didn't realize it. Now we've got our champion back," says Zahner.

If it sounds like there's competition among states for champion status, that's because there is. Another crown recently reclaimed from New Mexico is that of the Arizona walnut (Juglans major). In that case, the New Mexico champ had two trunks that split below chest level. Zahner realized the tree was measured incorrectly when he saw its picture. (The Register stipulates the largest trunk must be measured 4 1/2 feet above the ground.)