The MAB Program United States of America
Biosphere Reserve Information - General Description
Organ Pipe Cactus
General Description
Organ Pipe Cactus Biosphere
Reserve and National Monument is situated in the Sonaran desert in southwestern
Arizona at the border to Mexico. Wide alluvial basins separated by steep
mountain ranges characterize the topography of the area. The area represents
well the predominantly desert scrub vegetation of the Sonoran Desert, including
the organ pipe cactus (Stenocereus thurberi), a large cactus rarely found in the
United States but common in Mexico.
Three major plant associations of the Sonoran desert are represented in the
area: the Arizona upland with saguaro cactus (Cereus giganteus), paloverde (Cercidium
spp.) and organ pipe cactus; the California microphyll with creosote bush (Larrea
tridentata) and bursage (Ambrosia spp.); and floristic components normally
associated with the Mexican Gulf coast association elephant tree (Bursera
microphylla) and senita cactus (Cereus thurberi). There are some desert riparian
and relict oak woodlands. 49 native mammals occur within the monument, including
the endangered Sonoran pronghorn (Antilocapra americana sonoriensis).
The entire area, with the exception of the upper parts of the mountains, has
been modified by cattle grazing in the past. This activity is thought to have
originated in 1699 and continued until 1978, when the remaining livestock were
removed. Though the extent of modification is mostly unquantified, it has
resulted in visible soil erosion and some floral species composition changes.
Organ Pipe Cactus is part of the International Sonoran Desert Alliance (ISDA)
which includes citizens, native Americans, business leaders and organizations of
the United States and Mexico (including the Alto Golfo de California Biosphere
Reserve) which are concerned with the western Sonoran Desert. ISDA has developed
several culturally and environmentally focused community-based activities
Last updated: 06/27/2005