| An endemic flora comprised of caespitose perennials occurs on the Claron Formation in Red Canyon, Utah. These endemic calciphiles are apparently restricted to eroded knolls and scree slopes that support a sparse forest of mixed conifers. The purpose of this study was to better understand the restriction of the endemics to the relatively barren Claron Limestone and their absence from an adjacent sagebrush (floodplain) community. Edaphic factors that might be significant to species distribution were investigated using comparative analyses for scree slope and floodplain sites. In addition, seed viability and germination traits, growth form adaptations, reproductive strategies, mycorrhizal associations, and shade tolerance of the endemics were studied. Mineral nutrient concentrations (optical emission spectrometry) found in soils and dry tissue samples from the scree slope and adjacent floodplain (control) indicate that neither of the soils appears to be deficient in plant nutrients nor toxic to plants. Bioassays have demonstrated seed germination and seedling growth to be approximately equivalent in both scree slope (19% sand, 54% silt, and 27% clay) and floodplain (39% sand, 47% silt, and 14% clay) soils. Soil chemical and physical properties (i.e., alkalinity, cation exchange capacity, clay mineralogy, salinity, surface temperature, moisture-holding capacity, and moisture availability) are similar in both soils and seem insignificant to endemic plant distribution. Vesicular-arbuscular mycorrhizae were present on 5 out of the 10 endemic species sampled and may be beneficial to establishment on shallow soils derived from the Claron Limestone. Greenhouse shade experiments indicate that the endemic, Silene petersonii, may be shade intolerant which might contribute to its exclusion from the floodplain community in which midday canopy shade (irradiance) may inhibit germination. Seedlings of the endemic species were not observed on either the scree slope or in the floodplain. Endemic plant reproduction appears to be primarily vegetative. The restriction of Red Canyon endemics to the Claron Limestone may be a situation in which an edaphic substrate is occupied by a suite of endemic species because it provides a habitat with relatively low competition (for light) from the zonal vegetation. Slope inclination, microtopography, instability, and disturbance also may play minor roles in the restriction of the calciphile endemics. |
