The Influence of Several Range Improvements on Estimated Carrying Capacity and Potential Beef Production

Abstract

A simple calculation is proposed for estimating carrying capacity of range sites based on seasonal forage quality and standing crop. The model estimates animal unit days a pasture can support. Potential beef production of a particular site was estimated by multiplying animal unit days by average daily gain as indicated from forage quality. Improved and unimproved portions of 4 plant communities (grassland, mixed conifer, lodgepole pine, and moist meadow) were compared for carrying capacity and potential beef production. Improvement generally resulted in large increases in both carrying capacity and potential beef production; however, only in the case of the grassland did range improvement extend the period during which weight gains could be expected. Calculations indicate that energy generally became limiting before crude protein. Forage quality was insufficient to maintain weight gains of growing animals after mid-summer. Advantages and limitations of the calculations are discussed. Livestock production from rangelands could be increased if management was more closely coupled to seasonal changes in forage quality (Vavra and Raleigh 1976). Extending the period during which adequate nutrients are available to livestock has been accomplished by using seeded pastures to complement native range (Currie 1969, Smoliak and Slen 1974) and by grazing diverse vegetation types during the periods they are most likely to provide adequate nutrition (Valentine 1967). However, determining the optimum period of use for individual pastures may be difficult when many plant communities and/or range improvements are involved. A model of seasonal carrying capacity and potential animal production on various sites would help a manager in formulating a livestock management plan. Carrying capacity models based on nutritional requirements have been used to evaluate wildlife habitat (Wallmo et al. 1977, Mautz 1978, Hobbs et al. 1982). Hilken ( 1984) used a carrying capacity model to help evaluate competition between livestock and big game. The objective of the present study was to assess the impact of several range improvements on potential livestock carrying capacity and weight gain. We used a simple model, a data base consisting of seasonal curves of standing crop and forage quality of important forages species, and NRC (1970) nutritional requirements in our calculations. Study Sites Materials and Methods The study sites, which represented 4 plant communities, were located in Grant County, Ore. Plant community types were: (I) Authors are former research assistant 2nd professor of range nutrition. respectively. Oregon State University. Eastern Oregon Agricultural Research Center. Union 97883. Svejcar is currently research agronomist. USDA-AR& Southwestern Livestock and Forage Research Station, El Reno. Okla. 73036. The authors wish to thank an anonymous reviewer for comments which improved the manuscript. This report is Oregon State Agr. Exp. Sta. Tech. Paper 7065. The research was funded jointly by the Eastern Oregon Agr. Res. Center. Oregon State University. and the USDA Forest Service. under Project 1701 of the Pacific Northwest Forest and Range Exp. Sta. Manuscript accepted February I. 1985. JOURNAL OF RANGE MANAGEMENT 38(5), September 1985 395 moist meadow, (2) bunchgrass grassland on deep soil, gentle slopes, (3) lodgepole pine (Pinus contorta Dougl.)-pinegrass (Culamagrostis rubescens Buckl.)-huckleberry (Vaccinium scoparium Leiberg), and (4) mixed conifer-pinegrass-ash soils (Hall 1973). A portion of each study site had been improved. The improvements were as follows: (1) the moist meadow had been seeded to intermediate wheatgrass (Agropyron intermedium (Host.) Beauv.), timothy (Phleum pratense L.) and smooth brome (Bromus inermis Leyss.) about 15 years prior to sampling; (2) the grassland had been seeded to intermediate wheatgrass and alfalfa (Medicago sutiva L.) 3 years prior to sampling; (3) the lodgepole pine site had been thinned 14 years prior to sampling, but had not been seeded; and (4) the mixed conifer site had been commercially logged and seeded to timothy and orchardgrass (Dactylis glomerata L.) 2 years prior to our first sampling. Primary forage species on the unimproved portion of each plant community were: (I) the moist meadow was dominated by cinquefoil (Potentilfu sp.) and wyethia ( Wyethiu amplexicaulis Nutt.); (2) the grassland was mostly bluebunch wheatgrass (Agropyron spicutum (Pursh.) Scribn & Smith) and Idaho fescue (Festuca iduhoensis Elmer), but Sandberg’s bluegrass (Pea sandbergii Vasey) and junegrass (Koeleriu cristota Pers.) were also present; (3) the lodgepole pine understory was principally pinegrass (also the case on the thinned site); and (4) the mixed conifer understory was dominated by pinegrass and snowberry (Symphoricarpus albus (L.) Blake). A more detailed description of study sites can be found in Svejcar and Vavra (1985).