Bristlecone Pine (Pinus Longaeva) in Relation to Environmental Factors and Soil Properties in East-Central Nevada

TitleBristlecone Pine (Pinus Longaeva) in Relation to Environmental Factors and Soil Properties in East-Central Nevada
Publication TypeThesis
Year of Publication1972
AuthorsScott, B R
Academic DepartmentWatershed Management
UniversityUniversity of Arizona

The study was made of tree and stand characteristics of bristlecone pine (Pinus longaeva Bailey) as they relate to the environmental factors and soil properties in east-central Nevada. The pine sites studied were located on comparatively dry, rocky, exposed mountain slopes in the 9,000-to 11,000-feet elevation zone. The tree-growth characteristics studied were height, diameter, live bark index, percent of live crown, and two tree-ring parameters: mean ring width and mean sensitivity. Stand characteristics measured were basal area cover, density, and tree-spacing. Associated vegetation was identified and inventoried. Environmental factors and soil properties measured were percent slope, exposure, soil parent material, stone content, soil pH, total nitrogen, organic carbon, and clay. Bristlecone pine was found on two geologic substrates in the study areas—quartzite glacial moraine and limestone. The two substrates are similar in that they both appear to be excessively well drained because of high porosity of the geologic materials. Bristlecone was lacking on the sites underlain by quartzite bedrock except for isolated trees on exposed outcrops. Bristlecone pine often constitutes only a small percentage of the total cover on the more favorable sites within its tolerance range. On such sites limber pine (Pinus flexilis James) and Engelmann spruce (Picea Engelmanni Parry) generally dominate the stands. Bristlecone pine’s subordinate status on sites where growing conditions are relatively good (and stands are denser) is perhaps indicative of the species’ intolerance of shade. On the more adverse sites bristlecone pine often forms essentially pure, although sparse, stands. Regression analyses (both simple and multiple) and analyses of variance revealed that tree growth, as measured by mean ring width and tree height, was better on sites where moisture conditions were favorable, e.g., on north and east exposures as opposed to south and west exposures, and where soils were high in organic carbon, nitrogen, and clay. Year to year variability in growth, as measured by mean sensitivity, was greatest on sites with steep south- or west-facing slopes where soils were lowest in nitrogen, organic carbon, and clay, and highest in stone content. These results indicate that tree-growth on these adverse sites appears to reflect climatic fluctuations more so than trees on the relatively good sites. Leaf water potential of bristlecone pine and associated plants was measured both in the field and under controlled conditions in the laboratory. Results indicate that bristlecone pine apparently has the capacity to withstand high internal water stress in comparison to other non-desert conifers. Furthermore, the trees appear to be able to maintain lower leaf-water stress than some associated plants growing under similar conditions. These features may account in part for bristlecone pine’s dominance on the harsher sites.