THE IMPORTANCE OF OLNEYA-TESOTA AS A NURSE PLANT IN THE SONORAN DESERT

The function of Olneya tesota (ironwood) as a nurse plant and habitat modifier species in the Sonoran Desert was evaluated at five study sit es (using 75 250-m(2) sample plots) from Bahia Kino, Sonora to Organ P ipe Cactus National Monument, Arizona. Beneath the canopy of O. tesota trees 75 perennial plant species were found. A principal component or dination of the plots created three groups: southern, perturbed and pr otected sites. A strong triple association of columnar cacti, big shru bs with berry type fruits and O. tesota was detected. The relationship s of Lophocereus schottii and Peniocereus striatus with O. tesota were studied in more detail. Significant differences in soil surface tempe ratures and stem temperatures of P. striatus were detected beneath the shade of O. tesota trees compared with soils and plants in open space s. Olneya tesota must be considered as a habitat modifier species with ecological and conservational importance to the plant communities in the Sonoran Desert.