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An ecological study of the Ashnola bighorn winter ranges Demarchi, Raymond Alexander

Abstract

An ecological study of the important winter ranges of the Ashnola population of California bighorn sheep (Ovis canadensis californiana Douglas) was conducted from May 1963 through August 1964. Emphasis was placed upon the floristic composition, productivity, soils and the use by cattle, deer and bighorn of the ranges. The principal climax community between 3500 and 4500 feet is dominated by Agropyron spicatum and Koeleria cristata; above 4500 feet, often to 6200 feet, it is dominated by Agropyron spicatum and Festuca idahoensis. Both communities have developed on Rego Dark Gray soils. Overgrazing of the climax communities leads to serai communities dominated by Koeleria cristata and Poa secunda in the lower situation and Artemisia frigida and Koeleria cristata in the higher situation. Other serai communities which have arisen through overgrazing on Orthic Black soils are dominated by Poa pratensis, Poa secunda, or Bromus tectorum together with Stipa columbiana. The use by domestic cattle and, on some areas, the combined use by cattle and deer, are the principal factors presently maintaining the seral communities. Since bighorn use of the winter ranges occurs primarily after maturation of the forage, most areas heavily utilized by bighorn and not abused by cattle were found to be in the climax state. Bighorn were shown to have an affinity for the climax Agropyron - Koeleria and Agropyron - Festuca communities and utilized them three times more than seral communities. Chemical analysis revealed that by N. R. C. (1957 & 1963) feeding standards recommended for domestic sheep and cattle the seven forage species which compromised more than 95 percent of the bighorn winter diet contained sufficient crude protein, fat, fibre, ash, nitrogen free extract and calcium for maintenance. However, by the same standards, all species and notably the grasses, were deficient in phosphorus. Low phosphorus and moderate calcium levels produced unfavourable calcium:phosphorus ratios by mid-winter. Stipa columbiana, a principal increaser species and an unimportant item in the bighorn winter diet, was inferior to the other species investigated. Agropyron spicatum, a decreaser species and the most important bighorn food species, appeared to be the most nutritious grass. The retrogression of Agropyron spicatum dominated climax communities caused by past overgrazing by domestic stock, present forage competition with domestic stock, and possible phosphorus deficiencies are believed to be the principal factors presently limiting the bighorn population.

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