Plants are a vital component of biodiversity but are facing a high rate of extinction worldwide. In the United States, 57 percent of federally listed species are plants. The San Francisco Peaks ragwort (Packera franciscana) is an endemic plant species that occurs only in upper tree-line and alpine habitats of the San Francisco Peaks in northern Arizona. P. franciscana is federally listed as threatened due to its narrow geographic distribution, apparent specificity to volcanic talus habitat, and concerns over recreational impacts and climate change.
Due to limited area for upslope migration, a warming climate could lead to local extinction of this rare species. There is also concern that climate-induced changes in growth and reproduction could be a prelude to a population crash. Research on population stability and flowering or fruiting rates is critically important to the recovery and long-term management of P. franciscana.
Researchers used two recreational trails (Humphrey's Peak Trail and Weatherford Trail) which pass through the species’ elevational distribution as sampling transects to estimate population density and distribution. It was not possible to sample farther from the trails due to loose volcanic talus and consequent disturbance of the plants.
The researchers measured the density of P. franciscana ramets (upright stems), flower or fruit productivity, and the population centroid elevation (the weighted average of elevational abundance) where the population intersects each trail. Sample points were established systematically at 25 meter intervals along each transect.
In mid-September of 2010 and 2011 on the Humphrey’s Peak Trail and from 2009 to 2013 on the Weatherford Trail, the researchers counted P. franciscana ramets within 12 1-m2 frames at each sample point arranged along the trail edge. Counts were separated into vegetative, flowering, fruiting, or both within each frame. Coordinates for latitude, longitude, and elevation were made for each sample point with sub-meter accuracy using GPS.
Between-year comparisons of ramet density, population centroid elevations, and mid-September flowering fruiting counts were not significantly different for the Humphrey’s Peak Trail in 2010 to 2011 or the Weatherford Trail from 2009 to 2013.
Population density and elevation of the population centroid estimates for P. franciscana appear to be stable; therefore, the 5-year Weatherford Trail data set may be used as a baseline to track future plant migration on a fine spatiotemporal scale, an approach that could apply to other threatened alpine species.
Use of a zero-inflated negative binomial response variable distribution allowed statistical inference for both sampling hits and misses, which give ecologists and land managers an additional method to monitor changes in distribution and abundance.
Researchers are currently preparing a manuscript on another single mountain endemic plant species in the La Sal Mountains of Utah using a similar approach. They are starting to analyze multi-species plant assemblage data from four alpine sites in the Southern Rockies using an elevational gradient, species occurrence approach to detect current species-specific distribution trends for elevational migration and to establish baseline data sets for the detection of future elevational shifts by species.
Fowler, J.F. and S.T. Overby. 2016. Snow duration effects on density of the alpine endemic plant Packera franciscana. Western North American Naturalist 76(3): in press.
Sieg, C.H., J.F. Fowler. Ecology of a threatened, single mountain endemic plant species Packera franciscana (San Francisco Peaks ragwort). [webinar]. RMRS Research Priorities Sneak Peek Seminar Series: Species Endangerment. May 7, 2015.