Mixed Forests of Red Fir and White Fir in Yosemite National Park, California

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Abstract
Thirty mixed strands of white fir (A. concolor) and red fir (A. magnifica) were sampled in the ecotone between montane and subalpine forests (1950-2500 m) in Yosemite National Park, California. Detrended correspondence analysis and direct gradient analysis revealed that red fir predominates above 2260 m on steep slopes characterized by acidic substrates and open canopied forests. Below 2260 m, white fir predominates on xeric aspects characterized by higher soil fertility and greater canopy closure. Closed forests on mesic sites between 1950 and 2300 m include strands dominanted by either (or both) species. Patterns of habitat segregation between these 2 dominant congeners are believed to be related to growing season length, nutrient availability and increased importance of windthrow at higher elevations. The sparse ground layer has maximum cover and species richness on mesic sites at lower elevations, where ferns and herbs are most conspicuous. Shrubs and saprophytes/low ericads show less elevational/topographic restriction, favoring canopy gaps and shaded areas, respectively.