Date of this Version
US Army Corp of Engineers ERDC/CERL TR-05-32
Researchers monitored the threatened plant, purple amole (Chlorogalum purpureum var. purpureum) at Fort Hunter Liggett, California, from 1998 to 2004. The objectives of this research were to complete a statistical analysis of these data to evaluate: (1) demographics; (2) trends in population density; and (3) the relationship of purple amole to associated species, biological soil crusts, and disturbance. Overall, purple amole was most likely to flower and have greater seed production when it attained about 8 leaves or widths of 7 to 8 mm for its widest leaf, revealing a clear relationship between plant size and successful reproduction and seed set. Mortality and dormancy rates were estimated at 10 and 23 percent per year, respectively. Presumably, dormancy occurred, as mapped individuals were absent periodically throughout the monitoring. Density of purple amole was positively correlated with native species and presence of biological soil crusts; relationships to disturbance type were not apparent. Power analyses revealed that purple amole should be monitored at least 10 years to detect increases or decreases of 10 percent for mature plants (4 or more leaves). Due to greater variability, 10 to 20 years of monitoring are recommended to detect similar changes for 1 to 3-leaved plants.