Natural Range of Variation of Red Fir Forests in the Bioregional Assessment Area
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Natural Range of Variation of Red Fir Forests in the Bioregional Assessment Area Marc D. Meyer, Southern Sierra Province Ecologist, Pacific Southwest Region Table of Contents Introduction ....................................................................................................................................................3 Physical setting and geographic distribution .............................................................................................3 Geographic Distribution .........................................................................................................................3 Subspecies Distributions ........................................................................................................................3 Climatic Relationships ...........................................................................................................................3 Geology, Topography, and Soils ............................................................................................................4 Ecological setting .......................................................................................................................................4 Indicator Species and Vegetation Classification ....................................................................................4 Ecological Importance of Red Fir ..........................................................................................................4 Holocene Forest Development ...............................................................................................................5 Cultural and Socioeconomic Setting ..........................................................................................................7 Cultural and Socioeconomic Significance of Red Fir Forests ...............................................................7 Historical Setting .......................................................................................................................................7 European-American Settlement and National Forest Administration (1849-1945) ..............................7 Post-World War II (1945 to present) ......................................................................................................8 Methods..........................................................................................................................................................8 Variables, Scales, and Information Availability .........................................................................................8 Historic Reference Period ..........................................................................................................................9 NRV Descriptions and Comparisons to Current Conditions .........................................................................9 Function .....................................................................................................................................................9 Fire .........................................................................................................................................................9 Insects and Pathogens ..........................................................................................................................14 Wind and Volcanism ............................................................................................................................15 Climatic Water Deficit .........................................................................................................................16 1 Structure ...................................................................................................................................................17 Canopy Structural Classes and Landscape Patchiness .........................................................................17 Vertical Forest Structural Classes ........................................................................................................17 Canopy Cover and Height ....................................................................................................................18 Canopy Structural Complexity, Forest Heterogeneity, and Fragmentation .........................................18 Tree Densities, Size, and Size Class Distribution ................................................................................19 Basal Area ............................................................................................................................................20 Tree Spatial Patterns ............................................................................................................................20 Tree regeneration .................................................................................................................................22 Snags ....................................................................................................................................................22 Biomass ................................................................................................................................................22 Physiognomic Patterns – Seral Class Proportions ...............................................................................23 Composition .............................................................................................................................................23 Overstory Species Composition ...........................................................................................................23 Understory Species Composition .........................................................................................................23 Projected Future Conditions and Trends ......................................................................................................24 Background ..............................................................................................................................................24 Model Projections ....................................................................................................................................24 Summary ......................................................................................................................................................25 Acknowledgements ......................................................................................................................................26 Literature Cited ............................................................................................................................................26 Figure Captions ............................................................................................................................................38 Tables ...........................................................................................................................................................41 Figures..........................................................................................................................................................60 2 Introduction Physical setting and geographic distribution Geographic Distribution Red fir (Abies magnifica) forests are distributed throughout the Sierra Nevada immediately above the montane mixed-conifer and below the subalpine forest zones (Figures 1 and 2; Oosting and Billings 1943, Rundel et al. 1988). This forest generally occurs in a 300 to 500 m elevation width that extends from approximately 1800–2400 m in the northern Sierra Nevada to about 2200–2800 m in the southern part of the range (Fites-Kaufman et al. 2007, Potter 1998). Red fir extends from Sunday Peak in the northern edge of Kern County (Greenhorn Mountains) through the Cascade Range into southern Oregon as far north as Crater Lake National Park (Griffin and Critchfield 1972). Red fir is absent from the Warner Mountains and the Intermountain semides- ert province, including the White and Inyo Mountains of eastern California (Griffin and Critch- field 1972). Red fir forests are less common on the eastern slope of the Sierra Nevada and are seldom encountered south of Mammoth Mountain and north of the Kern Plateau (Potter 1998). Subspecies Distributions Populations of red fir are represented by three different varieties in the Sierra Nevada. Shasta red fir (Abies magnifica var. shastensis) occurs from Lassen Peak to Crater Lake National Park and has cones with partly exerted bracts. The second variety, A. m. var. magnifica, exists in the northern and central Sierra Nevada and has a hidden-bract cone type. Abies magnifica var. critchfieldii occurs primarily south of the middle fork of the Kings River and is distinguished from the Shasta red fir variety by smaller cones with protruding cone bracts (Lanner 2010). Until recently, this last variety in the southern Sierra Nevada was considered to be a disjunct popula- tion of Shasta red fir. However, geographic patterns of morphological variation, artificial cross- ing results, and recent molecular studies indicate that Shasta red fir consists of California red fir introgressed by noble fir (A. procera), and that A. m. var. critchfieldii has not hybridized with noble fir (Lanner 2010). Chloroplast genetic loci indicate that bothA. m. critchfieldi and A. m. magnifica share the same unique haplotype found in 100% of Sierra Nevada populations (Oline 2008). In contrast, the Shasta red fir variety contains multiple haplotypes, suggesting that