Influence of fire and climate change on vegetation in a mountainous national park

We used historical surveys from 1937 of dominant vegetation in Yosemite National Park, Sierra Nevada, California, USA as a baseline from which to measure patterns of vegetation change at landscape, plot, and stand levels. We measured vegetation change in three ways: first, historic vegetation maps were compared with modern maps to estimate shifts in the area coverage of dominant vegetation types; second, historic and contemporary vegetation plot data were used to determine the proportional frequency and elevational distribution of dominant species; and third, a subset of historic plots were re-visited to examine the change in species composition and abundance. We used these approaches to test two possible explanations for vegetation shifts—fire suppression and climate change.  We examined the historic and current extent of fire tolerant species and vegetation types, to see if they have systematically decreased, and whether the extent of fire intolerant types have increased.  We measured whether the distribution of vegetation types and species have increased in elevation.  We found significant shifts in dominant vegetation at all scales. There have been increases distribution and abundance of some fire tolerant species consistent with a fire suppression management regime.  We found significant upslope movements of some species, indicating a possible climatic warming explanation.  Both fire suppression and climate change have likely influenced the distribution of vegetation in Yosemite over the past 70 years.