At the highest elevations, the multi-decadal life cycles of tree species require monitoring techniques that are able to cover these extended timelines. In order to expand the temporal scale of change detection, repeat-photography research methods are applied to alpine and sub-alpine vegetation ecosystems in and around Yosemite National Park, California. Historic photographs provide the backdrop for a qualitative assessment of vegetation in sub-alpine and alpine vegetation zones.
Over 80 photographs from circa-1900 and circa-1985 were compared to those taken in 2008 to add an additional quarter century to previous change detection studies completed in the region. Photograph triplets showed evidence of 1) increased density of Krummholz stands, 2) increased density of sub-alpine forest stands at the tree line, 3) invasion of individual trees into meadows, 4) reduced instances of forest clearings and increased forest density, and 5) growth of trees on domes and rocky slopes. Evidence of upslope movement of the tree line was visible, confirming current knowledge of tree line systems in the American West, but contrary to previous studies conducted in this specific area.
I came across Prof. Vale's 1987 article "Vegetation Change and Park Purposes in the High Elevations
of Yosemite National Park, California" in 2006 and put it in a drawer, knowing it was something I wanted to revisit later in my graduate studies. Little did I know I would find myself trapsing the same ridges, meadows, and domes Prof. Vale and USGS photographers before him had previous traveled. Having spent over two decades in the Central Sierra in and around Tuolumne Meadows, I've had the opportunity to see the landscape change first hand. It is my hope that the field research presented within this site will be used, analyzed, and repeated into the future. There are numerous topics and projects which could and should utilize the data set organized by Prof. Vale and contained herein.
I would like to thank:
Prof. Thomas Vale, Barbara A. Holzman PhD and Andrew Oliphant PhD of San Francisco State University's Geography Department, and the National Park Service.
This research is dedicated to my family, who's dusty footsteps I will always follow across the High Sierra:
For Steve, Nancy, Natalie, and Jessica