Sixty thousand hectares of British Columbia's forest land were brushed in 1989/90, at a total cost of approximately $25 million. Manual brushing accounted for 37% (22 000 ha) of the area brushed, and 52% of the costs ($12 million). Increased expenditures on manual brushing are expected with increased commitment by both the Ministry of Forests and industry to improving the survival and growth of newly established forests and with reductions in the use of herbicides on forest land.
Some hardwood species (such as red alder, paper birch, trembling aspen, and black cottonwood) can be effectively controlled using cutting or girdling treatments. Manual cutting treatments can also be used effectively on slow-growing shrubs, such as white-flowered rhododendron, false azalea, and Vaccinium spp. However, single cutting treatments are generally not effective for controlling fast-growing shrubs or her-baceous vegetation. Instead, to control herbaceous vegetation, repeated treatments may be necessary within the same growing season. Bending herbaceous stems, rather than severing them, may be effective for reducing competition for light and physical damage to crop seedlings, and may result in less regrowth during the year of treatment than would cutting treatments.
Factors that influence the utility of manual brushing are: (1) the response of target species to manual treatment; (2) the growth response of the crop trees; (3) damage to the crop trees; and (4) administrative constraints limiting the use of manual brushing. Response of target vegetation varies with species, environ-mental conditions, and method and timing of treatment. Reports conflict on the growth response of crop trees released by manual cutting, and the information relating to the optimum stand age for treatment is not available. Damage can occur to crop trees from tools used for manual brushing, from sunscald caused by the sudden opening of the canopy, and from slash and animals. Because it is a labour-intensive undertaking, the use of manual brushing may be limited by the availability of contractors who do this type of work.
The cost of manual cutting or girdling is highly variable. On a province-wide basis, the average cost of all manual brushing treatments is $541/ha compared to an average of $289/ha for chemical brushing treatments. However, because of differences in the areas treated using manual and chemical methods, these relative costs may not reflect real differences. Factors that influence costs include: the composition, size and density of the brush or target species, the relative height of brush and crop species, terrain, availability of contractors, and specifications of the contract.
Further research is required to document the effectiveness of single and multiple manual brushing treatments, especially in comparison to herbicide treatments, and to identify optimum times for treatment.
Download LMR077 PDF file (400 KB)
To view this document you need the current version of
Adobe Acrobat Reader, available free from the
Adobe Web Site.
Updated November 26, 2008