Spatial and ecological analysis of red fir decline in California using FIA data

Graduation date: 2012Red fir (Abies magnifica) is a high elevation conifer generally growing between an altitude of 1,400 and 2,700 meters. In California, red fir grows in the Sierra Nevada, the Klamath Mountains, the eastern edges of the northern Californian Coast Ranges, and in the southern Cascades. Red fir commonly grows in pure stands and is often found in association with white fir (Abies concolor), lodgepole pine (Pinus contorta) or Jeffrey pine (Pinus Jeffreyi). Red fir is present in popular recreational areas including Yosemite, Kings Canyon, Sequoia and Lassen Volcanic national parks as well as the Mt. Shasta area and the Lake Tahoe region. Increasing and higher-than-expected red fir mortality and decline over the past five years has been observed in the central Sierra Nevada. This mortality and decline is seen as being caused by a complex interaction of biotic, anthropogenic and abiotic factors. The abiotic factors include drought, climate change (especially decreased snowpack), and the effects of changing fire regimes. The key anthropogenic factors are air pollution and forest management. The biotic factors include red fir dwarf mistletoe (Arceuthobium abietinum f. sp. magnificae), Annosus root disease (Heterobasidion annosum), Cytospora canker (Cytospora abietis), and the fir engraver beetle (Scolytus ventralis). Using USFS Forest Inventory & Analysis (FIA) plots at a density of one every 5.47 km (3.4 miles) across California allowed for the first stand-level analysis of the entire red fir distribution zone in California. The results show that mortality is increasing in red fir, which suggests that at least a short term decline is occurring. The rate at which mortality is increasing varies, depending on which analysis approach is used and decreases if recently burned plots are removed from the analysis. At the individual tree level, red fir mortality (all size classes) is occurring at an annual rate of 2.64%. Red fir dwarf mistletoe is the most significant factor in red fir mortality and decline based on our field observations and statistical analysis. There is a clear visual and statistical difference in forest health between areas that possess red fir dwarf mistletoe and those that don't. This remains true even when stands are heavily stocked and Annosus root disease is present, suggesting that Annosus root disease (which is common throughout the red fir distribution range) is greatly exacerbated by the presence of red fir dwarf mistletoe. Cytospora canker is associated with red fir dwarf mistletoe, and is likely a significant reason why the red fir dwarf mistletoe impacts red fir forest health so significantly. The only variation in spatial pattern of red fir mortality in California is an area of very low red fir mortality around Mt. Shasta (where red fir dwarf mistletoes does not occur). There was not a consistent correlation between red fir mortality and drought stress. The amount of fir engraver activity in California is not well characterized making it difficult to assess its' role in red fir mortality