INFREQUENT ESTABLISHMENT OF SEEDLINGS OF AGAVE DESERTI (AGAVACEAE) IN THE NORTHWESTERN SONORAN DESERT

Survival of seedlings of the common desert succulent, Agave deserti, required unusually wet years and the protection afforded by nurse plants or other shelters. The characteristics of seed germination and of seedlings showed that water stress in the seedling stage may be the most important factor affecting establishment. Leaves wilted irreversibly at an osmotic potential of ?1.6 MPa (–16 bars). Survival of seedlings required the generation of enough biomass during the first wet season to survive drought periods when the water potential of the soil was below ?1.6 MPa. Lengths of individual growing seasons and subsequent droughts were obtained from rainfall records for 1961 through 1978 for a site in the western Colorado desert. The length of the first major drought following germination apparently limited establishment of Agave deserti to only one year in the last 17. The favorable year, 1967, was consistent with the estimated year of germination of the six smallest Agave deserti observed in 1,500 m² at the field site.