Programs to manage competing vegetation in the southern interior of British Columbia have grown steadily since 1980, but quantitative information regarding the effect of treatment on conifer growth, plant community health, and livestock range productivity is required to justify the continued expenditure. In 1994–1995, it was estimated that the Kamloops Forest Region manually brushed 7500 ha at an average cost of $560/ha, and chemically brushed 1105 ha at an average cost of $360/ha (J. Boateng, pers. comm., March 1996). These high treatment costs must be weighed against both positive and negative effects on timber, range, and ecosystem values.
In British Columbia, forests provide 8.3 million ha of summer and fall livestock range, and account for nearly 80% of the total area of Crown land grazed. Clearcut logging enhances access for cattle, thereby increasing opportunities for range use, but range and silviculture management objectives for these sites often conflict. In the Kamloops Forest Region, approximately 3500 ha/year are seeded with domestic grass/forb mixtures to enhance the quality and production of cattle forage. Silviculturists, meanwhile, may prescribe brushing treatments in an attempt to reduce vegetation competition for conifer seedlings.
From a short-term silviculture perspective, brushing treatments are considered effective when they allow seedlings to release, improve growth rates, and reduce the time required to reach freegrowing. A number of vegetation complexes have been identified in the southern interior of B.C. that compete with conifer seedlings (Kimmins and Comeau 1990). However, little is known about threshold competition levels for these plant communities, above which seedling performance may be negatively affected, but below which it is unaffected or even enhanced. Over the long-term, treatment effects on site productivity and biodiversity are also important considerations.
From a range perspective, brushing treatments may severely reduce forage production and grazing capacity. For example, herbicides may injure both forbs and grasses (Conard and Emmingham 1984), resulting in shifts in species composition and the relative proportions of different forage types. Forb and grass species grazed by cattle vary in nutritive value, palatability, digestibility, and how highly they are preferred by stock (McLean and Tisdale 1960).
A series of research trials was established in 1986– 1987 in the Kamloops Forest Region to study the effectiveness of chemical and manual treatment methods for controlling competing vegetation, and to study the impact these brushing treatments have on the range resource. The three trials discussed herein are concerned with the release of lodgepole pine (Pinus contorta var. latifolia) growing in competition with the Dry Alder, Willow, and Pinegrass plant communities, as well as with the effects of chemical and manual brushing treatments on forage production and livestock use. It is hoped that the collection of both silviculture and range data will contribute to the development of guidelines to help managers integrate the use of these resources.
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Updated April 27, 2007