December 2012 Number 1 - Utah Native Plant Society

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Utah Native Plant Society allow flexibility for trail curvature (Figure 3). Sampling frames were omitted when they overlapped previously counted frames, covered recent trail maintenance areas, or covered vertical drop-off > 5 m. Counts of ramets with flower, fruit, or both were also made within each frame. Coordinates for latitude, longitude, and elevation were made for each sample point with a Trimble® Geo XT 2005 Series GPS. Descriptive statistics were calculated with SAS/STAT 9.1 (2002-2003). Population centroid was calculated as the mean elevation of occurrence weighted by the number of ramets / sample point. In July 2008, we mapped polygons of E. mancus patches with the Trimble® Geo XT 2005 Series GPS in three areas near and within Mt. Peale Research Natural Area, which is located in the Middle Group of peaks on La Sal Mountain. These polygons were plotted on a topographic map with ArcMap 9.2. RESULTS The September 2008 density estimate for P. franciscana along the recreational trail was 3.19 ramets / m 2 ramets in the 4 m band along the transect. A population centroid was located at 3667 m elevation. We counted a total of 1881 ramets of which 91 percent were vegetative, eight percent were in fruit, and one percent were flowering. Only seven ramets were in both flower and fruit. Figure 3. Arrangement and sampling sequence of 1 m 2 frames to measure ramet density. Erigeron mancus mapping work in July 2008 revealed a relatively continuous series of E. mancus patches along the west ridge up to Mt. Laurel in the La Sal Middle Group of peaks, from the talus field at 3725 m down to 3475 m just above treeline, as well as along the La Sal Middle Group crestline at 3650 m (Figure 4). Our observations indicate that it can be abundant within its microhabitat niche on dry, windy ridgelines but less abundant to absent on nearby more mesic midslopes DISCUSSION Phillips and Peterson (1980) reported a P. franciscana population density range of 50-370 plants per 100 m 2 on the San Francisco Peaks but did not clearly define plants as ramets or genets (clumps or clones) (Figure 5). However, later references to clump size would indicate that they were using the latter concept. On a per 100 m 2 basis, our density measurements are similar at the upper end of their density range (319 vs. 370), which is probably a reflection of the different “plant” definitions. Given the difficulty of defining and counting clumps and clones in the field, ramets provide a more accurate way to assess population density. Even though ramet density may inflate the number of functional plants, it is an accurate reflection of photosynthetic and reproductive potential. Phillips and Peterson (1980) also reported that 13% of the P. franciscana plants were adult (sexually reproducing) which again is comparable to the 9% of ramets we sampled which were flowering and/or fruiting. These results and our estimate of >18,000 P. franciscana ramets in a very small portion of its range would indicate that the species is persisting and reproducing. We interpret the successful production of fruit, which we observed actively dispersing by upslope winds in mid-September, as an indication that P. franciscana can sexually reproduce on the San Francisco Peaks. Seed viability studies may provide additional support for this interpretation. Examination of plant root systems would be necessary to determine if ramets originate from seed or from existing perennial rhizotamous clones. Rhizomes can produce large patches of ramets which may be the primary method of reproduction (USFWS 1983) but we also found single isolated ramets during our sampling which could be the result of seed dispersal or rhizome fragments moving downslope in the talus substrate P. franciscana inhabits. Plants inhabiting the upper portions of talus slopes would seem to be the result of seed dispersal since avalanches and downslope creep of talus fields would carry existing P. franciscana plants downslope. We noted dead P. franciscana plants at the base of some avalanche chutes. The population centroid of 3667 m we measured is above the 3525-3605 m elevation range for most P. franciscana noted by Dexter (2007) and near the upper end of the 3350-3750 m main 112
Calochortiana December 2012 Number 1 Figure 4. Erigeron mancus patches along the ridge up to Laurel Mt. and along the crestline of the Middle Group of La Sal mountain. occurrence range in earlier reports (Phillips and Peterson 1980, U.S. Fish and Wildlife Service 1983). However, our transect is located on a drier west-southwest slope which may account for the higher occurrence elevation. More mesic slopes may have lower patch centroids; a hypothesis we intend to test by establishing a northeast aspect, trail-side transect in 2009. We plan the second trail-side transect and annual measurements of both transects to detect P. franciscana population trends. Sampling in subsequent years may indicate trends in population density, changes in September phenology, or elevational migration within its habitat. We also plan to measure the change in E. mancus density along an elevational transect through the E. mancus patches shown in Figure 4. By measuring patch widths along this elevational transect, we can cal- culate patch size and, using our density measurements, can then estimate population size for this area. Changes in population density and the elevation of population centroids over time for both species may allow detection of climate change effects as well as provide managers with accurate data on which to base land and recreation use decisions. ACKNOWLEDGEMENTS Thanks to Amanda Kuenzi and Suzy Neal for help with fieldwork and to the Coconino and Manti-La Sal National Forests for funding support. Thanks also to Shaula Hedwall and Barb Phillips who reviewed the previous version of this manuscript and provided access to internal reports. 113
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December 2012 Number 1 - Utah Native Plant Society

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