Influence of Forest Management and Previous Herbivory on Cattle Diets

Abstract

Grazing cattle and timber harvest are common practices associated with forested rangelands. Therefore, the objective was to document the effects of timber harvest and herbivory on nutritional quality and botanical composition of steer diets in grand fir (Abies grandis [Dougl. ex D. Don] Lindl.) and ponderosa pine (Pinus ponderosa P. C. Lawson) forests. Three replicated grand fir sites were arranged as a split-plot design; timber harvest treatments—1) no harvest (CON), 2) thinning (TH), 3) clearcut (CL)— were whole plots, and herbivory treatments—1) large ungulate grazing (Graze), 2) wild ungulate grazing (CExc), and 3) exclusion of large ungulate grazing (TExc)—were the subplots. Three replicated ponderosa pine sites were arranged as a split-plot design; timber harvest treatments—1) CON and 2) TH—were whole plots, and herbivory treatments—1) GR, 2) BG, and 3) EX—were subplots. Diet samples were collected in June and August of 2001 and 2002. Crude protein, in vitro organic matter digestibility, acid detergent fiber, and neutral detergent fiber of the diets were only affected by season of use and were higher (P < 0.05) quality during the June grazing period. Botanical composition of diets was determined with the use of microhistological analysis of ruminal masticate. Within grand fir sites, graminoids were the major constituent in the diet (65%-91%), forbs intermediate (8%- 31%), and shrubs least (0.2%-3.5%). Within ponderosa pine sites graminoids were the major constituent in the diet (83%-88%), forbs intermediate (10%-14%), and shrubs least (2%-3%). Season of use did not affect (P > 0.10) botanical composition in either grand fir or ponderosa pine sites. Timing of grazing had a greater influence on diet quality; however, previous herbivory and(or) timber harvest had a greater influence on composition of diets than did timing of grazing.