This extension note summarises the one to five year responses of conifers and plant communities to operational brushing treatments on mesic sites in the southern interior of British Columbia. Manual, chemical, and grazing treatments were examined in the Fireweed, Fern, Mixed Shrub, Ericaceous Shrub, Dry Alder, Wet Alder, Aspen, and Mixed Broadleaf-Shrub complexes between 1991 and 2000.
Conifer responses were more variable than expected. Of the 15 brushing scenarios examined, survival improved only among spruce following manual cutting of the Ericaceous Shrub complex. In some cases, survival actually declined in the Mixed Broadleaf-Shrub complex because of increased mortality due to Armillaria root disease. Conifer diameter increased following: foliar glyphosate application to the Fern complex, manual cutting in the Mixed Shrub complex, and manual cutting and cut stump-glyphosate application in the Mixed Broadleaf-Shrub complex. Conifer diameter was unaffected by the treatments studied in all other complexes.
Vegetation recovery varied with treatment and complex. For example, most herb and short shrub-dominated complexes recovered within the season of single pass manual cutting and grazing treatments, but were reduced for at least five years following foliar glyphosate application. In the tall shrub and broadleaf complexes, shrubs and broadleaves generally recovered within three to five years of manual cutting, but crown cover was still substantially reduced five years following cut-stump glyphosate or girdling treatments. None of the brushing treatments had sustained effects on vascular plant diversity or richness, although specific species tended to decrease or increase following foliar glyphosate treatments in the short shrub and herb complexes, and following manual cutting in the tall shrub or broadleaf complexes.
Competition thresholds for conifer diameter growth were identified in all complexes and tended to be higher in milder than harsher biogeoclimatic zones, and higher among shade-tolerant than intolerant conifer species. The results of this study can be used to help focus brushing treatments in the most problematic areas, and to help with development of brushing prescriptions.
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Updated April 19, 2007