Saguaro recruitment over their American range: a separation and comparison of summer temperature and rainfall

Saguaro establishment is limited by moisture in the Sonoran Desert summer, presumably by summer rainfall. This study provides a first look at saguaro regeneration in 30 Arizona populations, and decouples summer rainfall from temperature, despite the strong relationship between these two variables, to determine the effects of each. Partial correlations quantify the success of temperature and precipitation in predicting high juvenile survival. This study finds that, once saguaros receive enough summer moisture (i.e. a population exists), highest maximum July temperature is the variable that best predicts recruitment. Although ultimately limited by water, saguaro regeneration appears to be influenced by maximum summer temperatures more than precipitation. The population structure for all populations shows a large spike among the youngest individuals, suggesting that recruitment continues in populations of this protected species. (C) 2003 Elsevier Ltd. All rights reserved.