| Abstract: 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. Growth trends
as documented included 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. The application of GPS and other technological
innovations allow for continued monitoring of upper elevation systems and
follow-up is strongly encouraged. Keywords:
Vegetation change, repeat photography, national parks, Yosemite National
Park, Sierra Nevada Mountains.
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