Mule Deer Numbers and Shrub Yield: Utilization on Winter Range

Abstract

Counts of mule deer (Odocoileus hemionus) fecal groups on 960, 100-ft2 circular plots located on three north-central Colorado winter range study areas of about 500 acres each, were related to mean forage yields in pounds (ovendry) per acre and mean utilization per plot (percentage weight) of true mountain mahogany (Cercocarpus montanus), antelope bitterbrush (Purshia tridentata), and big sagebrush (Artemisia tridentata) sampled on those plots from 1962 to 196S. Scatter diagrams and regression analysis revealed no significant ( P > O.OS ) correlations between the indices of deer numbers and mean yield or utilization of true mountain mahogany and antelope bitterbrush. Mean yield and mean utilization were significantly (P<0.05) correlated (r=-0.90) for true mountain mahogany but not for antelope bitterbrush (r =-0.S4). Inadequate sample sizes precluded similar analysis of big sagebrush. Neff (1968) has reviewed the technique of counting fecal groups as commonly used to assess population levels and distribution of big game. Counts of fecal groups on sample plots have also been used to approximate the weights of air-dry browse consumed by deer on winter range (McCain 1948, Leopold et al. 1951:110, Richens 1967: 654) as well as total forage produced (Giles and Snyder 1970:40). McCain and Taylor (1956:440) suggested that the percentage consumption of key browse species may be used to estimate trends in deer numbers. Julander et al. (1963:108) stated thatResearch on the relation of pellet group density to forage utilization is needed to determine whether pellet group counts might measure range use more accurately than utilization estimates alone. The objective of the present paper is to report on the relationship of counts of mule deer fecal groups to yields and utilization of three major shrub species on winter ranges. \Ve thank the many individuals who pro1A contribution from Colorado Federal Aid Project NV-105-R. 2 Present address: U. S. Forest Service, Intermountain Forest and Range Experiment Station, Boise7 Idaho. vided field or office assistance, particularly T. E. Hakonson, W. E. Jones, Jr., O. D. Markham, L. Nelson, Jr., K. A. Porter, and D. F. Stearns. J. Kovner and M. Morris, Biometricians, U. S. Forest Service, advised on the procedures used to estimate and analyze browse yield and utilization. STUDY AREAS AND POPULAT10N Three study areas, about 500 surface acres each, were selected to characterize the vegetation of winter range at different elevations within the Cache la Poudre River drainage, Roosevelt National Forest, northcentral Colorado. Soils are derived from schist, schist-gneiss, and granitic rocks (Lovering and Goddard 1950). Steep to precipitous slopes, with massive granitic outcrops are characteristic of each area. As described by Costello ( 1954), the mountain shrub community ( designated as shrub habitat in this report) comprised about 60 percent of each area, whereas the ponderosa pine-Douglas fir ( Pinus ponderosa-Pseudotsuga menziesii ) and ponderosa pine communities ( designated as coniferous habitat) comprised about 23 (Study Area 1), 38 (Study Area 2), and 28 (Study Area 3) percent of each area. Minor communities