Magnitude and Timing of the Tiltill Rockslide in Yosemite National Park, California

ABSTRACT Yosemite National Park, California, is one of the best-documented sites of historical rockfalls and other rock slope failures; however, past work shows that this record does not capture the infrequent largest occurrences, prehistoric events orders of magnitude larger than the largest historic ones. These large prehistoric events are evident as voluminous bouldery landslide deposits, permitting volume and age quantification to better understand local volume–frequency relationships, potential triggering mechanisms, and the hazard such events might pose. The Tiltill rockslide in northern Yosemite is one such example, consisting of 2.1 × 106 m3 ± 1.6 × 106 m3 of talus (1.5 × 106 m3 original volume of rock mass) that slid across the floor of Tiltill Valley, partially damming Tiltill Creek to create a seasonal pond that drains through and around the rockslide mass. This volume and the rockslide's effective coefficient of friction, 0.47, place it near the boundary between long-runout landslides and ordinary Coulomb failure. Although the rockslide superficially appears to consist of two separate lobes, statistically indistinguishable 10Be exposure dates from eight samples indicate a single event that occurred at 13.0 ± 0.8 ka. The age of the Tiltill rockslide and its relatively low elevation compared to equilibrium line altitudes at this place and time make glacial debutressing a highly unlikely triggering mechanism. Seismic shaking associated with fault rupture along the eastern Sierra Nevada is shown to be a plausible but unverified trigger.

Supplemental Material: Feldspar recycling across magma mush bodies during the voluminous Half Dome and Cathedral Peak stages of the Tuolumne intrusive complex, Yosemite National Park, California, USA

Consists of BSE and CL images of showing zonation in analyzed feldspar grains, EMPA analytical conditions, sample locations, and both whole rock and feldspar chemical data.

Supplemental Material: Feldspar recycling across magma mush bodies during the voluminous Half Dome and Cathedral Peak stages of the Tuolumne intrusive complex, Yosemite National Park, California, USA

Consists of BSE and CL images of showing zonation in analyzed feldspar grains, EMPA analytical conditions, sample locations, and both whole rock and feldspar chemical data.

The distribution of woody species in relation to climate and fire in Yosemite National Park, California, USA

Background The effects of climate on plant species ranges are well appreciated, but the effects of other processes, such as fire, on plant species distribution are less well understood. We used a dataset of 561 plots 0.1 ha in size located throughout Yosemite National Park, in the Sierra Nevada of California, USA, to determine the joint effects of fire and climate on woody plant species. We analyzed the effect of climate (annual actual evapotranspiration [AET], climatic water deficit [Deficit]) and fire characteristics (occurrence [BURN] for all plots, fire return interval departure [FRID] for unburned plots, and severity of the most severe fire [dNBR]) on the distribution of woody plant species. Results Of 43 species that were present on at least two plots, 38 species occurred on five or more plots. Of those 38 species, models for the distribution of 13 species (34%) were significantly improved by including the variable for fire occurrence (BURN). Models for the distribution of 10 species (26%) were significantly improved by including FRID, and two species (5%) were improved by including dNBR. Species for which distribution models were improved by inclusion of fire variables included some of the most areally extensive woody plants. Species and ecological zones were aligned along an AET-Deficit gradient from cool and moist to hot and dry conditions. Conclusions In fire-frequent ecosystems, such as those in most of western North America, species distribution models were improved by including variables related to fire. Models for changing species distributions would also be improved by considering potential changes to the fire regime.

Soil Enzyme Activity and Soil Nutrients Jointly Influence Post-Fire Habitat Models in Mixed-Conifer Forests of Yosemite National Park, USA

Disentangling the relative importance of habitat filtering and dispersal limitations at local scales (<1 km2) in shaping species composition remains an important question in community ecology. Previous studies have examined the relative importance of these mechanisms using topography and selected soil properties. We examined both topography and edaphic properties from 160 locations in the recently burned 25.6 ha Yosemite Forest Dynamics Plot (YFDP) in Yosemite National Park, California, USA. In addition to eight soil chemical properties, we included phosphatases and urease enzymes in a definition of habitat niches, primarily because of their rapid changes with fire (compared to soil nutrients) and also their role in ecosystem function. We applied environmental variables to the distributions of 11 species. More species–habitat associations were defined by soil properties (54.5%) than topographically-defined habitat (45.4%). We also examined the relative importance of spatial and environmental factors in species assemblage. Proportions explained by spatial and environmental factors differed among species and demographic metrics (stem abundance, basal area increment, mortality, and recruitment). Spatial factors explained more variation than environmental factors in stem abundance, mortality, and recruitment. The contributions of urease and acid phosphatase to habitat definition were significant for species abundance and basal area increment. These results emphasize that a more complete understanding of niche parameters is needed beyond simple topographic factors to explain species habitat preference. The stronger contribution of spatial factors suggests that dispersal limitation and unmeasured environmental variables have high explanatory power for species assemblage in this coniferous forest.

Reframing Native Knowledge, Co-Managing Native Landscapes: Ethnographic Data and Tribal Engagement at Yosemite National Park

Several Native American communities assert traditional ties to Yosemite Valley, and special connections to the exceptional landmarks and natural resources of Yosemite National Park. However, tribal claims relating to this highly visible park with its many competing constituencies—such as tribal assertions of traditional ties to particular landscapes or requests for access to certain plant gathering areas—often require supporting documentation from the written record. Addressing this need, academic researchers, the National Park Service and park-associated tribes collaborated in a multi-year effort to assemble a comprehensive ethnographic database containing most available written accounts of Native American land and resource use in Yosemite National Park. To date, the database includes over 13,000 searchable and georeferenced entries from historical accounts, archived ethnographic notebooks, tribal oral history transcripts and more. The Yosemite National Park Ethnographic Database represents a progressive tool for identifying culturally significant places and resources in Yosemite—a tool already being used by both cultural and natural resource managers within the National Park Service as well as tribal communities considering opportunities for future collaborative management of their traditional homelands within Yosemite National Park. We conclude that the organization of such data, including inherent ambiguities and contradictions, periodically updated with data provided by contemporary Tribal members, offers a rich, multivocal and dynamic representation of cultural traditions linked to specific park lands and resources. Indeed, some Yosemite tribal members celebrate the outcomes as revelatory, and as a partial antidote to their textual erasure from dispossessed lands. In practice however, as with any database, we find that this approach still risks ossifying data and reinforcing hegemonic discourses relating to cultural stasis, ethnographic objectivity and administrative power. By critically engaging these contradictions, we argue that one can still navigate pathways forward—bringing Native voices more meaningfully into the management of parks and other protected spaces, and providing a template useful at other parks for collaboration toward shared conservation goals.