Pack stock grazing capacity for wilderness meadows in Yosemite National Park

Jones, Laura; Baccei, Joy; Dickman, Erin

Pack stock (horses and mules) support recreational and administrative use in Yosemite National Park (Yosemite) and are permitted to graze in meadows. Grazing capacities are needed in Yosemite as one critical tool of an overarching management framework to address questions of appropriate spatial arrangement, timing, duration, and intensity of pack stock grazing in meadows within designated Wilderness and Wild & Scenic River corridors. The Wilderness Stock Use Framework outlines best practices for pack stock use management and monitoring that will guide where (site suitability), when (meadow opening dates), how (handling practices), and how much (site grazing capacity) use could occur at a given site in order to avoid, reduce, or mitigate impacts. In the Sierra Nevada, development of meadow grazing capacity models specific to pack stock use in a Wilderness context are limited, and current grazing capacity guidance specific to livestock may not sufficiently protect meadow ecological integrity. Hence, grazing capacities specific to Yosemite are needed. The park developed a preliminary grazing capacity for a high-use meadow in the Tuolumne River corridor (Ballenger 2013) which was applied to calculate Yosemite-specific pack stock grazing capacity for two high-use meadows, as outlined in the Tuolumne and Merced River Plans (NPS 2014a, b). This report builds on that work to develop a process of estimating preliminary grazing capacity more widely. This report does not determine grazing necessity in designated Wilderness areas, nor does it assess grazing appropriateness for particular sites. However, both of these topics are addressed in the Wilderness Stock Use Framework report. We explored several model inputs including forage area, forage production, allowable use, consumption rate, and grazing efficiency. We included most of these as explicit inputs to our resultant model, but excluded grazing efficiency. However, we show how grazing efficiency is implicit in forage production estimates. We carried over some model inputs as previously presented by Ballenger (2013), such as meadow area and pack stock consumption rates. In other cases, we modified metrics to incorporate new information or to facilitate broader application to a greater number of sites. We tailored a Yosemite-specific approach leveraging a unique dataset characterizing 77 meadows, 57 of which are available to grazing, with 44 of those in the Tuolumne River watershed and 13 in the Merced River watershed. Of these 57 meadows, a total of 47 meadows have stock camps associated with them: 35 of 44 meadows in the Tuolumne River watershed, and 12 of 13 meadows in the Merced River watershed. The dataset contained spatial cover values for dominant plant species, bare soil extent, total vegetation and plant litter obtained from plots spaced on a grid sampling approach across the meadow (Ballenger et al. 2010). We determined meadow hydrologic types—hydric, mesic, or xeric—based on wetland indictor ratings and an estimate of forage availability based on the proportion of forage species dominating a site. Additionally, we obtained data for meadow size and elevation from a Geographical Information System GIS. Therefore, we were able to estimate site-specific productivity values as an input to preliminary grazing capacities. Given variability in meadow elevation, size, type, and species composition, application of these data allow us to highly refine site specific grazing capacity among meadows. We applied a range of utilization rates (i.e. 5%, 25%, and 35% of total biomass productivity) to be allocated for pack stock consumption to an empirical relationship from a Yosemite-based study that correlated levels of pack stock use with levels of acceptable ecosystem change in meadows (Cole et. al. 2004). We formulated how the grazing management goal can be framed in terms of acceptable level of changes in meadow characteristics.

Pack stock grazing capacity for wilderness meadows in Yosemite National Park

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