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Effects of forest roads on the growth of adjacent lodgepole pine trees in the Williams Lake area of B.C. Bowering, Michael Scott


This study examines the effects of roads on the growth of adjacent lodgepole pine (Pinus contorta Dougl. var. latifolia Englm.) trees near Williams Lake, British Columbia. Three questions were addressed in this research: 1) Do roads result in increased diameter or height growth along the road right-ofway edge? 2) If increases occur, how far do they extend from the edge? 3) What are the stand level impacts of any increase in growth? Forty-four plots, ranging from 0.04 to 0.24 ha in size were established and measured in 1999. Plot ages ranged from 37 to 121 years, road widths from 5.3 to 38.5 m, and basal area densities from 14 to 45 m2 ha"1 . Beginning at the edge, five zones were established at 0 to 5 m, 5 to 10 m, 10 to 20 m, 20 to 30 m, and 30 to 40 m from the edge. Zone 5, at 30 to 40 m from the edge, was used as a baseline for comparison. On average, a 31.3% (using a 95% C.I.; 14.2% to 48.4%) increase in basal area per ha relative to the baseline in Zone 5, occurred within the first 5 m. Mortality was found to be lowest at the edge. As Zone 1 was 5 m wide, this translated into 1.56 m (or 13.6%) of the average 23.4 m road width (using a 95% C.I.; 0.71 to 2.42 m) that is recovered from the increase in basal area for an average stand. If both sides of the road were similarly impacted, then an equivalent of 3.12 m of growing space would be recovered. These results are similar to those by other researchers. Differences in the Zone 1 basal area per ha values relative to Zone 5 were significantly correlated to plot basal area per ha only. Other variables such as road width and edge aspect were not significantly correlated with the relative basal area per ha in Zone 1. The growth rates of trees in the 5 m edge zone, scaled for the 5 years prior to road establishment, differed significantly from growth rates in other zones. The growth rate of trees in the first 5 m increased by 32.1% on average, for the 3 to 15 years after the road opening was established. Significant differences were not found in the bole ellipticity, relative to road orientation. No corresponding increase in average basal area per tree or in average height was noted. The stands sampled in this study were comprised mostly of lodgepole pine, were relatively free of selective cutting and were away from other edges or openings. The results should, therefore, be applicable only to lodgepole pine stands and caution should be used in applying these results to stands with management treatments other than the road, particularly with the cutting of stems at the road edge. Key words: Road edge effects, linear openings, growth and yield, basal area increment, bole ellipticity, edge distance, recovered growing space, Pinus contorta Dougl. var. latifolia Englm., Williams Lake British Columbia.

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