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 per imeter, which had been established in both tundra and forest-tundra in 1973 were relocated in 1990. These showed that total vascular plant c over had reached prefire levels after 22 years, that tall shrubs had b ecome dominant in the tundra and that biomass was now sufficient to su pport another fire. Cryptogams showed minimum recovery between the two studies. 3 In previously treed areas postfire densities of Picea mari ana and Picea glauca were much lower than before. Betula papyrifera an d Populus balsamifera, however, showed an increase in density and had extended their range into previously treeless areas. 4 The results obt ained have implications for vegetation changes in the Circumpolar Nort h related to global warming. It is predicted that deciduous tree speci es with long distance seed dispersal mechanisms will increase in abund ance and will invade the tundra in a stepwise fashion after each fire. This will be most noticeable near northward flowing rivers because th ese valleys provide the habitat for outlier tree populations and are t herefore a major source of propagules.