Prescribed burning impacts on some coastal British Columbia ecosystems

Prescribed burning is widely used as a forest management tool; however, its long-term impacts on site productivity must be better understood to meet planned burn objectives. MacMillan Bloedel (now Western Forest Products Inc.) and the Canadian Forest Service began a study of the effects of prescribed burning on fuel consumption, tree growth and site nutrition in 1985. This paper quantifies the impacts of fires of different severity on woody debris and soil organic horizons. Three low-severity spring burns, two high-severity fall burns and two unburned controls were established on three sites near Port Alberni, on Vancouver Island, British Columbia. Most of the low-severity spring burn area was accidentally reburned during an adjacent high-severity fall burn, resulting in a very high-severity burn. The major differences in impacts between spring and fall burns were greater consumption of forest floor and increased mineral soil exposure on fall burns. The reburned area had forest floor consumption and mineral soil exposure similar to those in the adjacent fall burn, but also exhibited greater large woody fuel consumption. Total slash consumption significantly increased with increasing fire severity, while consumption of forest floor, slash plus forest floor, depth of burn, and mineral soil exposure were all significantly greater on fall burns compared to those in spring burns.