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Plant Species' Range Shifts in Mountainous Areas
Frei, E., Bodin, J. and Walther, G.-R. 2010. Plant species' range shifts in mountainous areas -- all uphill from here? Botanica Helvetica 120: 117-128.

More often than not, when temperatures rise in mountainous areas, indigenous plants tend to migrate upward toward cooler temperatures to escape the increasing heat. There are, however, exceptions to this general rule; see Crimmins et al. (2011). And now we have a second set of evidence for this phenomenon.

What was done
Frei et al. set the stage for their study by noting that "Rubel (1912) and Braun (1913) published data on the distribution of the alpine and nival flora in the region of Engadine valley in south-eastern Switzerland," which data "provide information on both the species' upper range limits and localities of lowest detected occurrences in the past within the whole study region," thereby enabling them to "combine and analyze available data from the literature (Grabherr et al., 2001; Camenish, 2002) and [their] own data (Walther et al., 2005; Burga et al., 2007) regarding the upper limit of species distribution on mountain summits in the Swiss Alps, and contrast these findings with new data for the species' lower elevational limit in the same region in summer 2006, resurveying the surrounding area of the localities where the species' lowermost occurrences were described in the historical literature," which thus allowed them "to study shifts at both the upper and lower ends of species distributions that have occurred since the beginning of the 20th century along elevational gradients."

What was learned
As would be expected, the three researchers report "there was a strong trend towards an increase in species richness per summit, including 33 species that were recorded for the first time on any of the investigated summit areas." These species, in their words, "experienced a consistent upward shift exceeding 100 elevational meters, and 49 out of the 125 investigated species shifted upwards to a present altitude which is higher than any reported occurrence in the region one century ago." Five species, however, "retained stable distributions in terms of both maximum altitude and number of summits they had colonized," while other species showed "a shift in the downward direction," and some "decreased in the number of summits they occupied as well as the altitude of their occurrence on particular mountains." At the lower range limit, on the other hand, Frei et al. found that "the majority of the species remained at the same altitude or were detected at lower altitudes than reported in the past, resulting in a non-significant overall difference in elevation for the resurveyed species at their lower range limit."

What it means
Although there is indeed a general tendency for plant species to move upward in elevation at their cold-limited range boundary in response to rising temperatures, some remain stationary and some even move in the opposite direction, while at their heat-limited range boundary, many do not move at all, as explained in detail in our major report The Specter of Species Extinction: Will Global Warming Decimate Earth's Biosphere?

Braun, J. 1913. Die Vegetationsverhaltnisse der Schneestufe der Ratisch-Lepontischen Alpen-Ein Bild des Pflanzenlebens an seinen aussersten Grenzen. Denkschr Schweiz Nat forsch Ges 48: 1-347.

Burga, C.A., Frei, E., Reinalter, R. and Walther, G.-R. 2007. Neue Daten zum Monitoring alpiner Pflanzen im Engadin. Ber d Reinh-Tuxen Ges 19: 37-43.

Camenisch, M. 2002. Veranderungen der Gipfelflora im Bereich des Schweizerischen Nationalparks: Ein Vergleich uber die letzten 80 Jahre. Jahresber Nat forsch Ges Graubunden 111: 27-37.

Crimmins, S.M., Dobrowski, S.Z., Greenberg, J.A., Abatzoglou, J.T. and Mynsberge, A.R. 2011. Changes in climatic water balance drive downhill shifts in plant species' optimum elevations. Science 331: 324-327.

Grabherr, G., Gottfried, M. and Pauli, H. 2001. Long-term monitoring of mountain peaks in the Alps. In: Burga, C.A. and Kratochwil, A. (Eds.). Biomonitoring: general and applied aspects on regional and global scales. Tasks for vegetation science 35. Kluwer, Dordrecht, Germany, pp. 153-177.

Rubel, E. 1912. Pflanzengeographische Monographie des Berninagebietes. Englemann, Leipzig, Germany.

Walther, G.-R., Beissner, S. and Burga, C.A. 2005. Trends in the upward shift of alpine plants. Journal of Vegetation Science 16: 541-548.

Reviewed 25 May 2011