Subproject Summary

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Introduction:

After harvesting, sites in the Interior Cedar-Hemlock Dry Warm subzone (ICHdw) frequently regenerate to rich, brush dominated communities that can inhibit successful conifer establishment. Located on the lower valley slopes of south-eastern British Columbia, the ICHdw subzone also features other important land uses that make forest management complex and controversial. In addition to being the most diverse subzone in the province in terms of tree species, this subzone often provides critical winter and spring ungulate habitat, and can be important as a domestic water source. As a result of these conflicting resource uses, herbicides are rarely an option for controlling competition to tree regeneration.

The Redfish Creek Manual Brushing study was established in 1987 to examine the cost and productivity of motorized manual brushing treatments (Holmsen and Whitehead, 1988). The original study design also accommodated longer-term follow-up of the biological effectiveness of motor-manual brushing.

Objectives:

• The 1997 remeasurement of conifer and vegetation response data was used to compare brushing treatment vegetation , stocking and conifer response 10 years after trial establishment.

Treatments:

Layout:

• Brushing was carried out during July 1997. Operators were instructed to "...cut all non-crop vegetation as low to the ground as practical..." (Holmsen and Whitehead, 1988).
• Each of plots 10-13 consisted of a 50 m by 50 m treatment plot with the treatment applied to the entire plot (Figure 1. (k jpg).
• For the purpose of the 1997 plot remeasurement, five 50 m² (r=3.99 m) assessment subplots were established in each treatment plot.
• Vegetation, crop tree and silviculture survey assessments were all conducted within these five subplots.
• Crop tree selection orders were: western larch , Douglas-fir and ponderosa pine as the preferred species; and grand fir, paper birch, lodgepole pine, western redcedar and western hemlock as acceptable species with birch as the species of last choice.
• Target stocking was 1800 trees/ha, with an inter-tree spacing of 2.5 m (1.5 m minimum) to a maximum of 9 trees per plot.
• All well-spaced crop trees were chosen for individual stem assessments (total height, basal diameter, diameter breast height, condition and vigor).
• For each well spaced Douglas-fir, ponderosa pine and larch, heights for 1995, 1993, 1991, 1989 and 1987 were estimated based on stem internodal distances.

Sites:

1. Redfish Creek

Major Findings:

1997 Remeasurement of Blocks 10-13:

Vegetation cover exceeded 120% in all blocks, with birch, ceanothus, thimbleberry, Douglas-fir and ponderosa pine as the leading top five species. The upper canopy in all treatment plots was dominated by broadleaf and conifer species in varying proportions. Total vegetation cover in the brushed blocks was found to be significantly greater than that in the control block. The total number of species found in each plot suggested there were approximately 20% more species in the area brushed three times compared to any of the other plots (45, 47, 47, 56 total species respectively for control (Figure 2. (120k gif)), brushed 1X (Figure 3. (125k gif)), 2X, 3X (Figure 4. (110k gif))).

Brushing reduced the density and size of birch and promoted the growth and survival of shade intolerant conifers and other understory vegetation. The total number of well spaced and free growing crop trees did not differ between the brushed and control areas (Table 1.).

In general, it was found that the brushing treatments significantly increased the size of the Douglas-fir (basal diameter) over those found in the control. Acceptable well spaced ponderosa pine were not found in the control however, brushing three times significantly increased tree height over brushing once or twice.

Manual brushing of an established birch/shrub brush complex can promote the establishment of a conifer dominated mixedwood stand. Failure to provide conifer release treatments will promote the establishment of a birch dominated stand at the expense of shade intolerant species. Brushing at least once can significantly increase ponderosa pine and Douglas-fir stocking however, intensive brushing regimes (at least three times) may be required to promote ponderosa pine height growth. Brushing at least twice may be required to significantly improve Douglas-fir diameter growth. Brushing birch more than once appeared to have no significant effect on total birch density.

Observations should not be taken without consideration of other observations and conclusions from similar research trial sites due to the lack of true replication in this demonstration (pseudo replication). The results from a single study are applicable to that site only and repeated studies at different locations are necessary to increase interpretation confidence.

References and Publications (Click on Highlighted References to Obtain an Electronic Copy in PDF Form):

Harper, G.J., R.J. Whitehead, and C.F. Thompson. 1998. A comparison of manual brushing treatments in the ICHdw at Redfish Creek - 10 year results form Blocks 10-13. E.P. 1995. Extension Note In Press. B.C. Ministry of Forests, Research Branch, Victoria.

Holmsen, S.D. and R. Whitehead. 1988. Comparison of clearing-saw cutting attachments for weeding young conifer plantations. Can. For. Serv. FRDA Rep. 028. Also FERIC Special Rep. SR-52.

Thompson, C.F. and P. Bauer. 1998. Ten-year results from a motor-manual brushing trial for conifer release in the ICHdw. In Press. JMJ Holdings Inc. Nelson, B.C.

To obtain any publications that are not highlighted click here.

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Last Updated: May 29, 1998.