Available at: https://digitalcommons.calpoly.edu/theses/3169
Date of Award
9-2025
Degree Name
MS in Biological Sciences
Department/Program
Biological Sciences
College
College of Science and Mathematics
Advisor
Dena Grossenbacher
Advisor Department
Biological Sciences
Advisor College
College of Science and Mathematics
Abstract
As climate change progresses, alpine plant communities are predicted to shift upslope as they track temperature over time. Relative to lowland environments, alpine areas are experiencing a faster rate of temperature change due to a phenomenon referred to as elevation-dependent warming. A common approach for tracking plant communities shifts over time, is to conduct resurveys of the same area at several time points, as the Global Observational Research Initiative in Alpine Environments (GLORIA) has done on mountain summits around the world since 2001. In 2011-2013, GLORIA developed a supplemental survey method whereby belt transects were established downslope of summits in order to detect elevation-based changes within a mountain slope. Initially, they established belt transects across five alpine slopes in the Great Basin region of California, providing insights into community turnover in water-limited alpine environments. However, they have yet to establish transects in less water-limited alpine areas, such as the west slope of the Sierra Nevada. Here we fill this gap, by establishing 41 transects on four Sierran alpine slopes in Yosemite National Park in 2023-2025. At each site, a series of 100-meter belt transects are situated 25-vertical meters apart on southwest-facing slopes, extending from treeline to ridgeline. Each transect is split into 5-meter segments surveyed by identifying all species and completing point-intercept surveys. Community composition was similar across sites with similar species appearing in high abundance, and 36-60% of variation in species composition explained by elevation at each site. We found that there may be a greater number of undetected species on Mt. Dana compared to the other sites. In addition to these baseline trends, we also explored inter-observer error whereby species are misidentified or missed altogether, leading to differences between surveys due to observers rather than species turnover. To quantify inter-observer error, we surveyed a subset of 115 segments with two observer teams on the same day, and compared their species lists using the Sorensen dissimilarity index. Inter-observer error was higher on Mt. Dana (20%) than Mt. Lewis (10%) and increases with higher vegetation cover at both sites. Aggregation of morphologically similar species did not reduce inter-observer error in our study. The identity of the observer team did not have a significant effect on the relationship between species richness and elevation. The information acquired in this study may help National Park staff to make informed management decisions when conserving alpine communities and informing interpretation of change over time in the future.