Ecological Relationships of Bristlecone Pine

Abstract

Functional relationships between bristlecone pine (Pinus longaeva Bailey)1 growth characteristics and environmental factors were investigated near Wheeler Peak and Bastian Peak in E-central Nevada. Because of bristlecone pine's intolerance to shading it constituted only a small percentage of the total tree cover on sites favoring good growth rates and dense timber stands. On such sites limber pine (P. flexilis James) and Engelmann spruce (Picea engelmanni Parry ex Engelm.) dominated the stands. On harsher sites bristlecone pine often formed essentially pure, although sparse, stands. Regression analyses (both simple and multiple) and analyses of variance revealed that bristlecone pines are faster growing, taller, straighter and less sensitive to climatic fluctuations on sites where moisture conditions are favorable. Organic carbon, clay and mean air temperature accounted for 83% of the variation in mean annual growth rates of bristlecone pine. Organic carbon and mean air temperature accounted for 55% of the variation in mean sensitivity (a measure of annual variation in ring width) of the trees. Maximum tree age is associated with harsh growing conditions which result in slow growth rates and dense, highly resinous wood. 1D. ?. Bailey (1970) demonstrated seveial important differences between the bristlecone pines and the Rocky Mountain bristlecone pines (Pinus aristata) as described by Engelmann. He proposed that the Great Basin population be considered a separate species, viz., Pinus longaeva Bailey. Nomenclature for other plant species follows Munz and Keck (1959). Introduction Bristlecone pine (Pinus longaeva Bailey) grows and attains great longevity on dry, rocky subalpine habitats in the southwestern United States. Trees over 3000 years old are common in particular habitats and several trees in excess of 4000 years have been reported in California (Schulman and Ferguson, 1956) ; only one bristlecone pine over 4000 years has been found in Nevada (Currey, 1965; Ferguson, 1970b). The longevity and esthetic appeal of the gnarled weather-beaten trees and their habitats have generated much interest among scientists and naturalists. Study of these ancient trees is contributing to many fields of science, including dendrochronology, climatology, geology and archaeology (Ferguson, 1968; Renfrew, 1973; LaMarche, 1974; Wilson, 1975). Yet, knowledge of the longevity and unique growth habit of bristlecone pine is still limited (LaMarche, 1969). The objective of this study was to identify environmental factors which might influence growth and distribution of bristlecone pine in E-central Nevada and to examine functional relationships between tree characteristics, environmental factors and soil properties. Study Area The study areas?Wheeler Peak and Bastian Peak?are E of Ely, Nevada, in the Snake and Schell Creek ranges, respectively, near the geographic center of the Basin and Range physiographic province of western North America. Near Wheeler Peak, bristlecone pine sites lie between 2900 m elevation and timbe rline (3200 m). Slopes are steep and covered with coarse, blocky, quartzitic glacial till. Soil derived from quartzite occupies interstices within the glacial till and supports sparse stands of bristlecone pine, Engelmann spruce (Picea engelmanni Parry ex Engelm.), limber pine (Pinus flexilis James) and scattered shrubs, herbs and grasses. On Bastian Peak, elevation 3274 m, bristlecone pine grows on soils derived from limestone. Slope gradients are steep on the E and W sides of the ridge but gentle to moderate near the crest. Limestone is exposed on the W side of Bastian Peak in