Barb Smith, Manti-LaSal NF and James F. Fowler, RMRS
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The La Sal Daisy, Erigeron mancus Rydb., is endemic to timberline and alpine habitats of the La Sal Mountains in Utah, an insular, laccolithic mountain range on the Colorado Plateau in southeastern Utah. It occurs in alpine herbaceous communities from timberline to the crestline of the La Sals.
Our primary goal in this study was to measure basic population biology parameters for the E. mancus population on the ridge from Mt. Laurel in the Middle Group of the La Sals west to treeline. We measured both E. mancus density and vascular plant species composition within 1-m × 1-m square frames along a ridgeline transect in mid-July near peak flowering time. Mean
density was 7.09 plants/m2 which yielded a population estimate of over 200,000 plants along Mt. Laurel ridge and its nearby southern crestline. Density does not appear to change significantly with elevation since the standard errors of the density estimates of the three main patches overlap. The elevation of the sampled E. mancus population centroid weighted by E. mancus density was 3537 m (12,330 ft) which is within the largest patch near a shallow windswept saddle. Vascular plant diversity along the Mt. Laurel ridge transects averaged
17 ± 0.58 SE species per square meter with a richness range of 10-26 species per square meter.
This study provides baseline data on the population biology of E. mancus which will then allow future re-measurements of density, population size, and elevational centroid to indicate population trends in response to climate change and anthropogenic stressors.