Observations of change in the cover of polargrass, Arctagrostis latifolia, and Arctic Lupine, Lupinus arcticus, in upland tundra on Herschel Island, Yukon Territory

Abstract

Herschel Island is located in the southern Beaufort Sea off the northern coast of the Yukon Territory and has acted as an excellent observatory of environmental change in the Canadian western Arctic. Between 1986 and 1999 the percentage cover of Polargrass (Arctagrostis latifolia (R.Br.) Griseb.) was observed to increase from 1% to > 5% in a dominant upland tundra vegetation type on Herschel Island. For example, the Arctic Willow/Dryas-Vetch type which occurs extensively on undulating portions of the island's upland and is associated with periglacial processes leading to patterned ground formation, has undergone a notable physiognomic change. Initially characterized by low shrubs and forbs, it is now characterized by grass. Similarly, the cover value of Arctic Lupine (Lupinus arcticus S. Wats.) increased markedly on many of the sites inventoried within this same vegetation type. Temperature records from Inuvik in the nearby Mackenzie Delta, suggest that the last 15 years have been warmer and somewhat drier than the 30 year normal in the region. Much of this increased cover of Arctagrostis latifolia and Lupinus arcticus is occurring on the bare patches of soil (frost boils or mud hummocks) that make up the patterned ground features of the vegetation type, an indication that these soil features generated and maintained by frost churning have stabilized to some degree. We speculate that periodic stabilization would be consistent with lower soil moisture levels in the active layer of underlying Cryosolic soils, resulting from warmer, drier climatic conditions.