POSTFIRE VEGETATION RECOVERY AND TREE ESTABLISHMENT AT THE ARCTIC TREELINE - CLIMATE-CHANGE VEGETATION-RESPONSE HYPOTHESES

1 A fire of unusually great severity (deep burning) burned across the forest-tundra ecotone near Inuvik, Northwest Territories from August 8 to 18, 1968. 2 Burned-unburned paired study sites around the fire perimeter, which had been established in both tundra and forest-tundra in 1973 were relocated in 1990. These showed that total vascular plant cover had reached prefire levels after 22 years, that tall shrubs had become dominant in the tundra and that biomass was now sufficient to support another fire. Cryptogams showed minimum recovery between the two studies. 3 In previously treed areas postfire densities of Picea mariana and Picea glauca were much lower than before. Betula papyrifera and Populus balsamifera, however, showed an increase in density and had extended their range into previously treeless areas. 4 The results obtained have implications for vegetation changes in the Circumpolar North related to global warming. It is predicted that deciduous tree species with long distance seed dispersal mechanisms will increase in abundance and will invade the tundra in a stepwise fashion after each fire. This will be most noticeable near northward flowing rivers because these valleys provide the habitat for outlier tree populations and are therefore a major source of propagules.