Background
The authors say "general circulation models predict that during the 21st century, anthropogenic climate forcing will lead to significant warming and induce changes to the global climate system that may cause rapid and sometimes drastic changes to vegetation [italics added]," citing the IPCC (2007) as the source of this claim.

What was done
In an attempt to further explore this predicted phenomenon, Hudson and Henry used open-top chambers to passively warm an evergreen-shrub heath, which was dominated by several shrub species and bryophytes, by 1.0-1.3°C over a period of fifteen years (during which time there was also a significant background warming) at Alexandra Fiord, Nunavut, Canada (79°N), which effort they describe as "the longest-running passive warming experiment in the Canadian Arctic."

What was learned
The two researchers from the University of British Columbia report that "experimental warming did not strongly affect vascular plant cover, canopy height or species diversity, but it did increase bryophyte cover by 6.3% and decrease lichen cover by 3.5%," although they note that "temporal changes in plant cover were more frequent and of greater magnitude than changes due to experimental warming." These findings thus prompted them to state that "this evergreen-shrub heath continues to exhibit community-level resistance to long-term experimental warming."

What it means
In about the only logical conclusion that could be reached, Hudson and Henry say their findings "support the view that only substantial climatic changes will alter unproductive ecosystems," such as the one they studied, in further support of which they note that other plant communities have also "exhibited strong resistance to simulated climate change manipulations (e.g. Grime et al., 2008), where resistance is defined as the ability of a community to maintain its composition and structure in the face of environmental change." And they amplify this conclusion by stating that "at other Arctic sites, lichen, bryophyte and evergreen-shrub dominated heaths were [also] less responsive to experimental warming than other plant communities," citing the studies of Hollister et al. (2005), Jonsdottir et al. (2005) and Wahren et al. (2005).

References
Grime, J.P., Brown, V.K., Thompson, K., Masters, G.J., Hillier, S.H., Clarke, I.P., Askew, A.P., Corker, D. and Kielty, J.P. 2000. The response of two contrasting limestone grasslands to simulated climate change. Science 289: 762-765.

Hollister, R.D., Webber, P.J. and Tweedie, C.E. 2005. The response of Alaskan arctic tundra to experimental warming: differences between short- and long-term responses. Global Change Biology 11: 525-536.

IPPC. 2007. Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC, Geneva, Switzerland.

Jonsdottir, I.S., Magnusson, B., Gudmundsson, J., Elmarsdottir, A. and Hjartarson, H. 2005. Variable sensitivity of plant communities in Iceland to experimental warming. Global Change Biology 11: 553-563.

Wahren, C.H.A., Walker, M.D. and Bret-Harte, M.S. 2005. Vegetation responses in Alaskan arctic tundra after 8 years of a summer warming and winter snow manipulation experiment. Global Change Biology 11: 537-552.