Sonora, a living desert

UNESCO Courier, Sept, 1996 by France Bequette

On the northern side of the border, the Organ Pipe Cactus National Monument (ORPI) was proclaimed a national monument in 1937, then a UNESCO Biosphere Reserve in 1976. South of the border, several areas that had been protected for a number of years - El Pinacate, the Gran Desierto de Altar, the upper reaches of the Gulf of California and the Colorado River Delta - were joined in a single Biosphere Reserve named Alto Golfo de California in 1995. Three years before saw the beginnings of a bold project for a Biosphere Reserve that would cover some 28,700 [km.sup.2] and encompass the entire Sonoran Desert, both its U.S. and Mexican sections. The idea emerged from a workshop attended by scientists and administrators from the two countries, who on the same occasion created the International Sonoran Desert Alliance (ISDA) in order to maintain an ongoing dialogue between Mexicans, Americans and Tohono O'odham Native Americans, and to integrate conservation, research, education and sustainable development.

Organ Pipe Cactus National Monument

The most spectacular part of the Sonoran Desert and the most typical of its ecosystem is probably the Organ Pipe Cactus National Monument, which covers 134,000 hectares on the American side of the border. Despite the aridity of the climate (an average of 23 cm of sporadic rain a year) and summer temperatures nudging 60 [degrees] Celsius, 574 of the 730 vascular plant species (or tracheophyta) in the desert are found there; and more than 90 per cent of these are endemic. The most impressive plants are the giant saguaro (Carnegiea gigantea), which has become the symbol of the area, and the Organ Pipe Cactus (Stenocereus thurberi). The commonest tree is the palo verde (Cercidium microphyllum) that blooms with small yellow flowers in the spring. There is also an abundance of jojoba (Simmondsia chinensis), agave (Agave deserti) and one-seed juniper (Juniperus monosperma).

There is also a wide variety of wildlife: 55 species of mammals, four species of amphibians, 43 species of snakes, 260 bird species and even one species of fish, the desert pupfish (Cyprinodon macularius eremus), that is unique to the United States. It may well seem strange to talk of fish and the desert in the same breath, but ORPI contains 11 springs, three of which are perennial. The largest is Quitobaquito which discharges nearly 130 litres per minute and sustains a pond and a green oasis. It was a vital staging-post for travellers 400 years ago as they passed along the Camino del Diablo on their way from Mexico to California in search of gold and other minerals. It was already a cross-roads at the time of the Hohokam culture between 300 B.C. and 1400 A.D.

But intensive agricultural development and urbanization in the neighbouring Mexican state of Sonora, especially since the installation of a high-voltage powerline at Hermosillo, are posing serious problems for ORPI. Over 200 wells pump 5,300 litres of water per minute from the groundwater of the Sonoyta River basin, i.e. two and a half times its replenishment capacity. Aerial spraying of crops and the introduction of cultivated exotic plants are added threats to the park's natural resources. On the American side unchecked irrigation has already caused the salination of 200,000 hectares of land.

ORPI is bordered on the west by the Cabeza Prieta National Wildlife Refuge, which was created in 1939 to protect the Desert Bighorn Sheep (Ovis canadensis mexicana) and the Sonoran Pronghorn Antelope (Antilocapra americana sonoriensis). In 1942, however, its 348,000 hectares became the second largest artillery range in the United States, now called the Barry M. Goldwater Air Force Range. The U.S. Air Force and Navy carry out air-to-air target practice all year long, and the ground is littered with unexploded devices and debris. Low-altitude flying by supersonic jet fighters frightens the animals, but experts admit that the refuge's environment is generally in excellent shape because access to it is severely restricted.

A study by Jennifer Jenkins of the Yale School of Forestry and Environmental Studies points up what she calls the "inconsistencies" of the refuge system. On the one hand refuges exist to protect biodiversity; on the other, they have to receive more and more tourists, hunters, and oil and mineral prospectors, and at the same time withstand the consequences of the intensive farming of neighbouring lands: pesticide ran-off and abstraction of groundwater supplies. A reform that would resolve these contradictions is underway.

The cinders of hell

The nature of Mexico's Pinacate and Gran Desierto Reserve is quite different. Essentially volcanic, the terrain in its northern sector resembles the moon's surface so strongly that American astronauts have trained there. There are more than 400 cinder cones, ten giant craters (more like meteor impact areas than volcano craters), lava flows and gently sculpted sand dunes that contrast sharply with the jagged silhouette of the mountains. There are more than 560 vascular plant species, 56 species of mammals (including the pronghorn), 43 species of reptiles, 222 bird species and 4 species of fish. Temperatures range between -30 [degrees] Celsius and +50 [degrees] Celsius.