Four decades of plant community change in the Alpine tundra of southwest Yukon, Canada.

Repeat measurements from long-term plots provide precise data for studying plant community change. In 2010, we visited a remote location in Yukon, Canada, where a detailed survey of alpine tundra communities was conducted in 1968. Plant community composition was resurveyed on the same four slopes using the same methods as the original study. Species richness and diversity increased significantly over the 42 years and non-metric multidimensional scaling indicated that community composition had also changed significantly. However, the direction and magnitude of change varied with aspect. Dominant species were not replaced or eliminated but, instead, declined in relative importance. Fine-scale changes in vegetation were evident from repeat photography and dendro-ecological analysis of erect shrubs, supporting the community-level analysis. The period of study corresponds to a mean annual temperature increase of 2 degrees C, suggesting that climate warming has influenced these changes.

Multi-decadal changes in tundra environments and ecosystems: synthesis of the International Polar Year-Back to the Future project (IPY-BTF).

Understanding the responses of tundra systems to global change has global implications. Most tundra regions lack sustained environmental monitoring and one of the only ways to document multi-decadal change is to resample historic research sites. The International Polar Year (IPY) provided a unique opportunity for such research through the Back to the Future (BTF) project (IPY project #512). This article synthesizes the results from 13 papers within this Ambio Special Issue. Abiotic changes include glacial recession in the Altai Mountains, Russia; increased snow depth and hardness, permafrost warming, and increased growing season length in sub-arctic Sweden; drying of ponds in Greenland; increased nutrient availability in Alaskan tundra ponds, and warming at most locations studied. Biotic changes ranged from relatively minor plant community change at two sites in Greenland to moderate change in the Yukon, and to dramatic increases in shrub and tree density on Herschel Island, and in subarctic Sweden. The population of geese tripled at one site in northeast Greenland where biomass in non-grazed plots doubled. A model parameterized using results from a BTF study forecasts substantial declines in all snowbeds and increases in shrub tundra on Niwot Ridge, Colorado over the next century. In general, results support and provide improved capacities for validating experimental manipulation, remote sensing, and modeling studies.

Vegetation, Microtopography, and Depth of Active Layer on Different Exposures in Subarctic Alpine Tundra.

Four slopes with different exposures (southeast-, southwest-, east-, and north-facing), but with similar gradients, elevations, and rock type, were studies in the Ruby Mountains of southwest Yukon Territory, Canada, Vegetation was best developed on the southeast facing slope, was successively less on east- and southwest-facing slopes, and least on the northfacing slope. Solifluction lobes were present in varying degrees, and their development largely followed that of vegetation in that they were best developed on the southeast-facing slope and least well developed on the north- and southwest-facing slopes. The vegetation occurred in sharply delineated communities across the lobes on the southeast-facing slope, and the communities repeated themselves in predictable patterns. The same communities were present on the east-facing slope, but were not as distinct. Plant cover was relatively impoverished on southwest- and north-facing slopes, where there fewer microhabitats and where soil, moisture, and temperature conditions were not found in favorable combinations. Depth of the active layer largely corresponded to the presence of vegetation and microtopography. The active layer was shallowest and most variable on the southeast-facing slope. Plant cover, in general, was more important than exposure in determining the depth of thaw.