Pack stock have been part of the history of Yosemite National Park, California, since the mid-1800s, and they continue to play vital roles in wilderness recreation and park operations. Releasing stock for grazing in meadows is a common practice for overnight stock users (figs. 1 and 2); however, grazing and trampling can negatively affect meadows by decreasing vegetation cover and productivity, shifting plant species composition, damaging streambanks, exposing bare ground, compacting soil, and increasing erosion (Miller and Donart 1981; Kauffman and Krueger 1984; McClaran and Cole 1993; Olson-Rutz et al. 1996; Cole et al. 2004). A recent study in Yosemite identified impacts on subalpine meadows linked to stock use (Ballenger et al. 2010). Park staff is addressing this issue through a science-based pilot stock management program that monitors use levels and area conditions and recommends best management practices to mitigate resource damage. Because commercial pack trips account for approximately half of overnight stock use in Yosemite, the park has used the Commercial Use Authorization (CUA) permit as an interim management tool, as it gives the park superintendent discretion to establish specific terms and conditions of use.
Figure 1. Pack stock graze at Dorothy Lake, July 2010, Yosemite National Park.
Figure 2. Pack stock at Emeric Lake in Yosemite, August 2006.
The pilot stock management program focuses on Lyell and Virginia canyons, northeast of Yosemite Valley, where approximately half of the park’s commercial stock use occurs. We chose these sites because of high use levels and impacts compared with other areas, diversity of the two areas, and relatively easy access for monitoring. In August 2009, an interdisciplinary team of park biologists, wilderness managers, and trail maintenance staff visited both areas to observe and discuss pack stock issues in the field. As a result the team developed recommendations for management actions, some of which were implemented following management approval the following season. For example, in 2010, Yosemite designated stock camps and holding areas in Virginia and Lyell canyons, identified access routes to and from the camps, and clarified locations of grazing areas. Packers are expected to use the depicted access routes and camp locations, which we provide in the form of maps with GIS locations, as a condition of their CUA permit. The number of sites where stock are permitted was reduced and may help decrease the amount of grazing in meadows until science-based grazing limits can be established.