Shrub Age Structures on a Mule Deer Winter Range in Colorado

Abstract

Age—determination techniques for selected shrub species utilized by deer were tested on known—age specimens and refined. Intact plants and descriptive data were collected on circular milacre plots in random locations in selected stands. Prepared specimens of Purshia tridentata and Artemisia tridentata were readily aged by crossdating xylem growth layers. Cercocarpus montanus proved difficult and supplemental ring counts were used, reducing accuracy of the age determinations. Ribes cereum samples were unsuitable for the techniques employed. Ages in years were estimated for 3,231 plants, and age structures were graphed by 5—year classes. The "die—away" curve is used as a hypothetical norm for self—replacing populations in the interpretation of age structures. Shrub age structures may reflect current and past reproductive success and, hence, successional status. Irregularities may be related to fires, climate, rodent seed—caching, reproductive cycling, and use by animals.