Ecosystems at high elevations, according to Price and Waser (2000), "may be especially sensitive to global warming, because productivity is limited to a snow-free growing season, and warming is expected to cause earlier snowmelt." To investigate this widely-held assumption, they suspended electric heaters above half of ten replicate plots on the slope of a small glacial moraine in west-central Colorado, USA. For the next five years, the heaters warmed the surfaces of the subalpine meadow ecosystem beneath them, and the authors observed what happened. Contrary to expectations, the experimental warming did not extend the duration of plant reproduction, nor did it change the composition of the ecosystem. The authors report, for example, that the warming "did not induce shifts in abundance of short-lived species, graminoids, forbs, shrubs, or in total vegetation cover." Neither did it affect species richness or species distributions along the elevation gradient of the moraine. In fact, they could not identify a single negative consequence of the additional warmth.
Riedo et al. (2001) investigated the consequences of simultaneous increases in surface air temperature and atmospheric CO2 concentration for a Swiss Alps pasture via a simulation model forced by a stochastic weather generator. They found that a 2°C temperature rise increased ecosystem evapotranspiration, but that a doubling the air's CO2 content reduced this impact while simultaneously enhancing ecosystem net primary production. The net result of the two environmental changes was thus a rise in ecosystem water-use efficiency and a 10% increase in soil carbon content.
In an experiment where only the air's CO2 content was increased, Schappi and Korner (1997) observed increases in the carbon/nitrogen ratios of the growing leaves of four different species of alpine plants, but no changes in the chemical composition of their leaves by the time they naturally senesced and fell to the ground. Hirschel et al. (1997) likewise found no compositional differences in the naturally-senesced leaf litter of an alpine grassland; but they observed that litter from high alpine sedges produced under elevated concentrations of atmospheric CO2 decomposed significantly slower than litter from similar plants produced under ambient conditions. Both of these phenomena tend to enhance soil carbon sequestration; and the finding of Arnone (1999) - that the symbiotic nitrogen-fixing Trifolium alpinum was not stimulated in any way by atmospheric CO2 enrichment - does not alter this conclusion.
In a study of real-world changes over time, Klasner and Fagre (2002) evaluated summer temperatures and spring snowpack over the period 1927-1991 in the McDonald Creek drainage basin of Glacier National Park (Montana, USA). In spite of periodic climate-alarmist claims of impending warming-induced disaster in this region, the authors' data revealed no net change in spring snowpack from the beginning to the end of the record. Likewise, there was no net change in summer minimum temperature; and there was an actual drop of approximately 0.7°C in summer maximum temperature. Hence, as would be expected on the basis of these observations, there were no altitudinal changes in the location of the alpine treeline, although there was a 3.4% increase in the area of tree coverage from 1945 to 1991, perhaps partially in response to the historical rise in the air's CO2 content over that period. In two mountain valleys of mid-Norway, however, Olsson et al. (2000) observed that grasslands and heathlands that had long dominated these areas are today "decreasing due to forest invasion," which they say is characterized by "the spread of subalpine woodlands, and a raised treeline."
In summary, in response to whatever environmental changes may be occurring in alpine ecosystems around the world, there appear to be few, if any, negative biological consequences.
References
Arnone III, J.A. 1999. Symbiotic N2 fixation in a high Alpine grassland: Effects of four growing seasons of elevated CO2. Functional Ecology 13: 383-387.
Hirschel, G., Korner, C. and Arnone III, J.A. 1997. Will rising atmospheric CO2 affect leaf litter quality and in situ decomposition rates in native plant communities? Oecologia 110: 387-392.
Klasner, F.L. and Fagre, D.B. 2002. A half century of change in alpine treeline patterns at Glacier National Park, Montana, U.S.A. Arctic, Antarctic, and Alpine Research 34: 49-56.
Olsson, E.G.A., Austrheim, G. and Grenne, S.N. 2000. Landscape change patterns in mountains, land use and environmental diversity, Mid-Norway 1960-1993. Landscape Ecology 15: 155-170.
Price, M.V. and Waser, N.M. 2000. Responses of subalpine meadow vegetation to four years of experimental warming. Ecological Applications 10: 811-823.
Riedo, M., Gyalistras, D. and Fuhrer, J. 2001. Pasture responses to elevated temperature and doubled CO2 concentration: assessing the spatial pattern across an alpine landscape. Climate Research 17: 19-31.
Schappi, B. and Korner, C. 1997. In situ effects of elevated CO2 on the carbon and nitrogen status of alpine plants. Functional Ecology 11: 290-299.