Environment in Relation to Age of Bristlecone Pines

Bristlecone pines (Pinus aristata Engelm.) locally attain ages over 4,000 years. In the White Mountains, California, old trees are widely distributed near the lower forest border, but are restricted to exposed, rocky areas at higher altitudes. Comparative aridity seems to be an important feature of the "old—age" habitat. Occurrences of older (1,5000—4,900 years) bristlecone pines in the moister mountain ranges of Nevade and Utah are analogous to those at higher altitudes in the White Mountains, suggesting that local edaphic and physiographic factors can offset the effects of a regional precipitation gradient. Attainment of an age greater that about 1,500 years apparently depends on the adoption of a strip—growth habit, which permits the aging bristlecone pine to maintain a nearly constant ratio of green to non—green tissue. Slow growth rates, wind damage, and soil erosion may be conducive to cambial area reduction. Other features of old—age stands, such as the wide spacing of the trees, the compactness of their crowns, the sparsity of litter, and the low density of the accompanying ground—cover vegetation, would also provide a measure of protection from fire and from competition, permitting the older trees to survive.