Diameter-Age Relationships of Two Species of Mountain Mahogany

Abstract

Diameter-age relationships of two species of mountain mahogany (true mountain mahogany and curlleaf mountainmahogany) were investigated. Data were taken from populations of true mountain mahogany in the Laramie Basin of Wyoming (Brooks 1962) and the Uintah Basin of Utah. Data for curlleaf mountain mahogany were obtained from populations in the Whitehorse mountains of Oregon, the Trout Creek mountains of Nevada (Dealy 1975) and from several areas in north-central Utah. Equations were developed for age prediction from stem diameters. Age prediction was most accurate within local population boundaries and less so when used to predict ages across population boundaries. Aspect was shown to be an important factor in influencing age prediction in curlleaf mountain mahogany. Variations in the growth rings of trees and shrubs have been used for years as dating techniques (Douglas 1935; Glock 1937) and to gain information about climatic differences of the past (Schulman 1956; Fritts 1971; Stockton and Meko 1975; Harper 1979). Ring-width variations have also been used to assess differences in the environments of selected habitats (Ferguson and Humphrey 1959; Fritts 1962; Stockton and Fritts 1973; Fritts 1974). Although trees have been the major object of such studies (Glock 1955; Authors are associate professor of botany and range science, Department of Botany and Range Science, Brigham Young University, Provo, Utah 84602; research scientist, Shrub Sciences Laboratory, U.S. Forest Service, Provo, Utah 84601; and range conservationist, Bureau of Land, Richfield, Utah 84701. Manuscript received March 30, 1979. JOURNAL OF RANGE MANAGEMENT 33(5), September 1980 Argeter and Glock 1965) papers dealing with shrubs can also be found (Ferguson 1958; Ferguson 1959; Ferguson and Humphrey 1959). The shrub studies have generally dealt with variations of moisture in the habitat or as aids to archaeological interpretation. Studies dealing with diameter-age relationships of shrubs and their values in the development of age-prediction models, interpretations of environmental factor differences, site-quality estimates, and measurements of successional trends are generally lessknown. The objectives of this study were: to assess the stem diameter-age relationships in true mountain mahogany (Cercocarpus montanus) and curlleaf mountain mahogany (Cercocarpus Zedifolius), to develop age prediction models from stem diameters, to assess the accurateness of the models within and between populations, and to evaluate the effects of aspect on the growth patterns of the shrubs and thus the predictive value of the models.