Postdispersal Reproductive Biology of a Mojave Desert Population of Larrea tridentata (Zygophyllaceae)

Abstract

The postdispersal reproductive biology of a California Mojave Desert creosote bush population was studied. Over 90% of the mericarps were dispersed during July and early August. Rodents (mainly Dipodomys merriami) destroyed 27.5% of dispersed mericarps, whereas birds and ants took negligible amounts. There was no significant carry-over of viable mericarps between reproductive seasons. Transplanted seedlings were eaten by Lepus californicus and/or rodents. Survival of exclosed transplanted seedlings increased with distance from mature Larrea shrubs. Seedlings growing naturally on the site were primarily found under mature perennials (including creosote bush), indicating that other factors override the distance-dependent mortality experienced by transplants. Xylem-ring counts of seedlings showed that past germination and establishment occurred in response to heavy late summer rainfall. Such rainfall patterns are unpredictable (occurring only 9 times during 41 years in this region) and appear to be the main factor limiting L. tridentata reproduction.