Population Dynamics and Age Relationships of 8 Tree Species in Navajo National Monument, Arizona

Abstract

The presence of 3 major archeological ruins dating from the I lth to 13th centuries (Woodbury 1963) provided the primary motivation for including Navajo National Monument in the National Parks System. Also included in the monument are some unique ecosystems, especially a small relict of mountain vegetation found in Betatakin Canyon. As visitor pressures mount annually, proper management of these unique ecosystems becomes highly important. Since trees are the dominant features of these ecosystems, and are central to management considerations, the present work has examined populations of 8 major tree species in the monument. The objectives of this study were, first, to develop age prediction equations for tree species growing in Navajo National Monument, and second, to assess the present age profiles, reproductive recruitment, and density relationships of these tree populations. Variations in the growth-ring widths of trees have been used for many years to date wood (Douglas 1935, Glock 1937) and to garner information on past climates (Fritts 1971; Stockton and Meko 1975; Dean and Robinson 1978; Harper 1979). Additionally, ring width variations have been studied to ascertain differences in the environments of selected habitats (Ferguson and Humphrey 1959, Stockton and Fritts 1973, Fritts 1974) and to assess site quality with reference to timber production (State 1966, Brickell 1968, Jones 1969). Although stem diameter measuresments have long been used to predict tree age and ascertain population status, it is difficult to use data from one area to extrapolate to conditions in other areas (Dealy 1975, Brotherson et al. 1980). Because of these difficulties and because of the absence of such data on northeastern Arizona plant communities, our studies provide useful baseline information.