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Natural revegetation of disturbed sites in British Columbia Errington, John Charles

Abstract

Factors affecting the natural revegetation of areas disturbed by airborne emissions were studied at the Anyox smelter on the northern coast of British Columbia. Revegetation of areas where vegetation and soil were removed by industry were studied on mine waste dumps on Vancouver Island, on mine wastes in the West Kootenays, and on abandoned logging roads on Vancouver Island and near Lumby. At Anyox, much of the direct evidence of fume damage was eradicated by a fire in 1942, which occurred eight years after smelting operations ceased. This fire encompassed a five-mile radius surrounding the smelter. Tree-ring analysis on surviving western hemlock trees, extending from the edge of the fire to the head of Alice Arm, showed a strong relationship between the tonnage of ore smelted and the radial increment. Tree growth was initially depressed when smelting began in 1914 and remained low until smelter operations ceased. At this time the growth dramatically increased, but by 1970 the annual radial increment had returned to a slow rate similar to before smelting operations began. Western hemlock was much less susceptible to fume damage than western red cedar. Although total fume kill occurred on western red cedar as far south as the Nass River, north to the head of Hastings Arm and East to the head of Alice Arm, total kill on hemlock took place within a few miles of the smelter. Fume damage was the heaviest near the smelter and near the head of Alice Arm where the topography confined the fumes, rendering them more effective. Within the area affected by the 1942 fire, revegetation was slow near the smelter and was more rapid near the mature vegetation. Seeds which are easily dispersed by light wind, were responsible for the majority of colonizing species many of which were found rarely in the surrounding unburned vegetation. On logging roads and mine waste materials, seed source availability appeared to be the major factor in determining the colonizing species. Light wind-blown seeds were the initial colonizers on coastal logging roads, and adjacent vegetation supplied the seed source for the interior logging roads. The establishment of salal through vegetative means was' observed to occur on coastal logging roads. Species with the ability to fix nitrogen, with the exception of alder, played a minor role in natural revegetation of most areas. Slow revegetation of large-scale disturbances was attributed partly to the lack of adequate seed. The most common cause of slow revegetation in most areas was moisture deficiency. Moisture availability on mine wastes at Cumberland appeared to be determined by slope, aspect, color, shading and mound height. On logging road surfaces, in both Lumby and coastal areas, a reduction in plant growth on steeper slopes was attributed to reduced moisture. Wind exposure was found to be the most important factor governing revegetation of mine wastes in the West Kootenays. Coarse textured material was related to a lower percentage cover of vegetation on the surface of coastal logging roads. Uniformly coarse textured material on the waste dumps in the West Kootenays precluded any significant statistical relationships. Coarse textured materials, nevertheless, had a general inhibitory effect on the rate of revegetation of many of the mine waste dumps. Steep unstable slopes were a major factor which prevented revegetation of West Kootenay mine wastes and on the upslope of road cuts. The scale of disturbance was found to magnify or obscure many of the factors important to successful plant colonization. The chemical composition of waste material, although studied only peripherally, did not appear to be a major factor in determining the revegetation of disturbed areas at the sites studied. Low pH values, which are often taken as a barometer of mine waste toxicity, occurred rarely. In many instances, high pH values may have prevented the successful invasion of acid-loving species. In applied reclamation procedures, it is mandatory that objectives for future land use be incorporated into planning, along with the anticipation of inhibiting factors. If no conditions are left which prevent plant growth, then reclamation will be straightforward and land use goals will be more easily satisfied.

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