To Unesco home page

To sitemap

To MAB home page title2.gif (2287 bytes)
      Biosphere Reserve Information

United States of America


  General Description   Organ Pipe Cactus Biosphere Reserve and National Monument is situated in the Sonoran 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.
  Major ecosystem type   Warm desert
  Major habitats & land cover types   Organ Pipe Cactus lies on an ecotone between arid thronscrub and true desertscrub. It comprises three major features: rockslopes, bajadas, and valley floor flats and also includes xeroriparian scrub. Vegetation: major canyons with extensive xeroriparian thicket overstories of mesquite, whitethorn and catclaw acacias, hopbush, desert and netleaf hackberry etc.; major thickets on bajadas dominated by blue paloverde, mesquite, ironwood, and catclaw acacia; bajada arroyos bordered by leguminous shrubtrees: open stands of ironwood, foothill paloverde, acacias and mesquite; valley floor thickets dominated by mesquite, creosotebush, blue paloverde, catclaw acacia, condalias and crucifixion thorn. Upland desertscrub on rockslopes is dominated by brittlebush, triangle-leaf bursage, jojoba, foothill paloverde, and mixed cactus. Upland desertscrub on bajadas is dominated by creosotebush and triangle-leaf bursage, foothill paloverde, mixed cactus etc. Open desert woodlands dominated by ironwoods and foothill paloverde shrubtrees. The flats are vegetated by creosotebush, white bursage, triangle-leaf bursage, and big galleta; or by saltbush assocations.
  Location   3200'N; 11250'W
  Area (hectares)    
  Total   133,882
  Core area(s)  
  Buffer zone(s)  
  Transition area(s) when given  
  Altitude (metres above sea level)   +335 to +1,472
  Year designated   1976
  Administrative authorities   Organ Pipe Cactus National Monument National Park Service
  Brief description   Comparative ecology
Rare/endangered species
Risk assessment
Ecosystem restoration
Watershed management
  Specific variables...    
  Abiotic   n.a.
  Biodiversity   Ecology, rare/endangered/threatened species, restoration/rehabilitation/redevelopment.
  Socio-economic   n.a.
  Integrated monitoring   Impact and risk studies/Environmental impact, management issues, watershed studies/monitoring.
  Contact address   William Wellman
Organ Pipe Cactus
10 Organ Pipe Dr.
85321 Ajo, Arizona
United States of America
  Telephone   (1.520) 387 7661 ext. 7500
  Fax   (1.520) 387 7144
  Web site
  Contact address   Bryan Milstead
Organ Pipe Cactus National Monument
10 Organ Pipe Dr.
85321 Ajo, Arizona
United States of America
  Telephone   (1.520) 387 7661 ext. 7112
  Fax   (1.520) 387 7144
  Web site

Last updated: 11/03/2005

To topTo MAB home pageTo UNESCO