Demography and Life History Characteristics of the Rare Kachina Daisy (Erigeron kachinensis, Asteraceae)

Abstract

-Erigeron kachinensis is a rare endemic of the Colorado Plateau regions of southeastern Utah and southwestern Colorado. It occurs in small, isolated alcoves (recessed areas in canyon walls) at seeps arising along canyon walls in sandstone substrates. One hundred randomly selected individuals of E. kachinensis within each of six alcoves in Natural Bridges National Monument, San Juan County, Utah, were monitored for 5 yr (1990-1994). Survival of the 600 individuals was followed over the monitoring interval. Vegetative and reproductive parameters were assessed for the survivors each year. Mortality varied among the study alcoves and individual size-classes. Mortality was heavily concentrated in the smaller size-classes. Growth rate accelerated with increasing size-class. Survival rate also increased with increasing size-class. Plants are long-lived; however, longevity is still unknown since mortality was not observed in the largest size-class. Fecundity was greatest for the largest sizeclasses, yet over 80% of the annual seed production came from the three smallest size-classes due to abundance of individuals in these size-classes. Populations varied with respect to plant size and resistance to environmental stressors. Matrix analysis demonstrated a finite rate of population growth of 0.75. However, observed size-class distributions of the six study populations over 5 yr of observation have never been stable. Maintenance of viable populations of the Kachina daisy is dependent on management actions that minimize disturbances (natural or anthropogenic) in the fragile hanging gardens that support the species.