Snow Duration Effects on Density of the Alpine Endemic Plant Packera franciscana

Abstract

Packera franciscana (Greene) W.A. Weber and Á. Löve (Asteraceae) (San Francisco Peaks ragwort) is an alpine-zone endemic of the San Francisco Peaks in northern Arizona. Previous studies have shown that P. franciscana is patchily distributed in alpine-zone talus habitats. The purpose of this study was to describe the relationship between snow duration and P. franciscana abundance. We established trailside transects through P. franciscana habitat along the Weatherford Trail to estimate the abundance of P. franciscana ramets. Snow-free and snowbed sample segments were chosen based on a 17 May 2013 snow photograph taken from within the Inner Basin of the San Francisco Peaks caldera. The section of the Weatherford Trail under snow on 17 May 2013 had a 5-year arithmetic mean of 1.53 ramets ⋅ m-2 (SE 0.37)—much less dense than the snow-free section which had a 5-year arithmetic mean of 7.17 ramets ⋅ m-2 (SE 1.09). The steep upper portion of talus slopes is known to move downslope faster than mid- and lower slope portions due to gravitational processes working on surface particle size, slope angle, and frost heave/needle ice during moist periods. Needle ice is known to uproot seedlings in other species. Active talus shift may inhibit P. franciscana colonization and growth on upper talus slopes via high seedling mortality in the snowbed zone during spring snowmelt.