What was done
In 2010, the authors visited a remote location in the Ruby Range Mountains of the Southwest Yukon of Canada, "near the head of a tributary of the Gladstone Lakes complex (61.38°N, 138.20°W) where four slopes result from the confluence of two ridges," which is where they say that "a detailed survey of alpine tundra communities was conducted in 1968." It was there that they resurveyed plant community composition "on the same four slopes using the same methods as the original study," between which two times they indicate there was "a mean annual temperature increase of 2°C," suggesting that climate warming was likely responsible for the changes they observed.

What was learned
The four researchers report that "species richness increased on all slopes, diversity increased on three of the four slopes, and community composition changed significantly on each of the four slopes, with the most significant change occurring on the southwest aspect." These changes, as they continue "were the result of two factors: (1) the addition of many new, less abundant, species and (2) the reduction in relative importance values of many of the most dominant species." And they say that the increase in species richness and diversity they observed "is consistent with the results of repeat surveys from several other alpine and subarctic sites," citing the studies of Kullman (2007), Holzinger et al. (2008), Vittoz et al. (2009) and Odland et al. (2010)," while noting that "dominant species were not entirely replaced or eliminated over the 42 years."

What it means
The results of this study suggest that as earth's climate warms and ever more species expand the cold-limited boundaries of their current ranges northward in the Northern Hemisphere, high-latitude ecosystems will likely begin to support a greater number of more diverse species, but without necessarily displacing the species that previously resided there.

References
Holzinger, B., Hulber, K., Camenisch, M. and Grabherr, G. 2007. Changes in plant species richness over the last century in the eastern Swiss Alps: Elevational gradient, bedrock effects and migration rates. Plant Ecology 195: 179-196.

Kullman, L. 2007. Long term geobotanical observations of climate change impacts in the Scandes of West-Central Sweden. Nordic Journal of Botany 24: 45-467.

Odland, A., Hoitomt, T. and Olsen, S.L. 2010. Increasing vascular plant richness on 13 high mountain summits in southern Norway since the early 1970s. Arctic, Antarctic, and Alpine Research 42: 458-470.

Vittoz, P., Randin, C., Dutoit, A., Bonnet, F. and Hegg, O. 2009. Low impact of climate change on subalpine grasslands in the Swiss Northern Alps. Global Change Biology 15: 209-220.