Variability in Juniperus in the Palo Duro Canyon of Western Texas

Abstract

The Palo Duro Canyon of the Texas Panhandle provides moisture and soil gradients which affect the distribution of vegetation. This study of Juniperus in the Canyon was undertaken to determine the nature and extent of hybridization among the species with emphasis on the relation between ecologic conditions and species composition of juniper populations. Two apparently distinct species complexes are found in the Canyon. The first involves Juniperus deppeana-pinchotti-monosperma; the second, Juniperus virgini- ana-scopulorum. While the mesic J. deppeana is neither in nor near the Palo Duro Canyon, some of its genes are apparently present in populations of I. pinchotii. Populations of J. pinchotii most resembling I. deppeana are in mesic sites within the Canyon, while those populations most resembling I. monosperma occupy more xeric sites. In the second complex, no typical I. virginiana is found in or near the Canyon; however, populations most resembling it are located in the mesic sites and those resembling I. scopulorum are in the more xeric sites. The Canyon junipers consist of J. pinchotti, I. monosperma, J. scopulorum. Also present in the Canyon are junipers intermediate between the nomenclatural type of I. pinchotii and I, deppeana, and junipers intermediate between I. scopulorum and J. virginiana. It is understood by biologists that the correlation of ecologic and taxonomic data succeeds best through integration of the array of fac- tors responsible for both habitat characteristics and existing species composition. The major ecologic factors of an area include those per- taining to physical geographic features, its geologic history, past and present watersheds and drainage basins, climatic conditions, soil types and their physico-chemical characteristics and interactions in com- munity dynamics. Useful taxonomic data include ascertainment of the distributional patterns of the systematic groups involved, implying a knowledge of environmental tolerance and preference of the groups as well as their relative genetic plasticities, some impression of his- torical factors, and a multi-character analytical procedure in the de- 1 This research was supported by a grant, GB-1860, from the National Science Foundation.