Altitudinal Limits To Plant Survival

Plants that live at high altitudes demonstrate a remarkable ability to survive in some of the most challenging environments on Earth. The permanent snowline is generally taken as marking the principal upper altitudinal limit for flowering plant colonization (Fig. 10.2). There are however, peaks or horns of rock that rise above the snow, ice fields known internationally by the Inuit term nunataks where plants can manage to live above the snow. These emergent mountaintops have sides that are too steep to support snow and ice accumulation, and provide bare ledges and crevices which serve as microhabitats for a few hardy mountain plants. Below the permanent snowline is the subnival zone. In terms of a major altitudinal zonation where regular plant colonization can be encountered, the subnival zone is normally the uppermost altitudinal habitat for plants on snow-covered mountains. Even here, however, the terrain is fragmented by gullies that vary from year to year in their retention of permanent snow. Nevertheless, a snow-free growing season of only a few weeks in the year provides a marginal habitat where a few species can succeed in growing and sometimes reproducing.

Subnival Plant

Fig. 10.2 The nival zone as seen on Mt Sefton 3151 m, Southern Alps, New Zealand, photographed in late summer. Note the extensive areas ofbare rock within the nival zone where local topography and wind reduce the snow cover creating potential plant habitats. Plants that live in this area are referred to as the nival flora.

As might be expected, the highest altitude records for flowering plants are found on tropical and subtropical mountains. In 1938 on Mount Everest (8848 m), Eric Shipton, the only veteran of all four 1930s British Everest expeditions, found Saussurea gnaphalodes, Asteraceae (Fig. 10.3), growing on scree at an altitude of 6400 m. Other species found on Mt Everest above 6100 m included Ermania himalayensis

(Cheiranthus himalaicus, Crucifereae) at 6300 m, and in the Caryophyllaceae, Stellaria decumbens and Arenaria bryophylla (Miehe, 1997).

These species survive at astonishing elevations on certain outstanding high mountains but this should not obscure the realization that every region has its own particular high-altitude flora, and plants that achieve altitude records in lower mountain ranges in temperate

High Altitude Mountain Plant

Fig. 10.3 Saussurea gnaphalodes, the highest species on Mt Everest recorded in 1938 by Eric Shipton at 6400 m. Photograph taken in Sichuan Province by Dr D. Boufford on the north side of the pass at Zheduo Shan (30° 4' 45" N, 101° 48' 27" E). Elevation 43704485 m. (Photo taken during a botanical and mycological inventory of the Hengduan Mountains, China, a project funded by the U.S. National Science Foundation (grant no. DEB-0321846 to D. E. Boufford) and the National Natural Science Foundation of China (grants no. 40332021 and 30420120049 to H. Sun).)

Fig. 10.3 Saussurea gnaphalodes, the highest species on Mt Everest recorded in 1938 by Eric Shipton at 6400 m. Photograph taken in Sichuan Province by Dr D. Boufford on the north side of the pass at Zheduo Shan (30° 4' 45" N, 101° 48' 27" E). Elevation 43704485 m. (Photo taken during a botanical and mycological inventory of the Hengduan Mountains, China, a project funded by the U.S. National Science Foundation (grant no. DEB-0321846 to D. E. Boufford) and the National Natural Science Foundation of China (grants no. 40332021 and 30420120049 to H. Sun).)

and arctic regions are just as noteworthy, even if it is at a lower altitude. In the European Alps the high-altitude record for a flowering herb is Saxifraga biflora. This is a very local endemic species confined to high altitudes and often remains covered in snow until the second week in July; it thus escaped the notice of early alpine botanists, being described first by the Swiss biologist, physician and poet Albrecht von Haller in 1768. The highest altitude so far reported for S. biflora is at 4450 m on the Dom du Mischabel (Fig. 10.4). The species occurs also at 4200 m on the Matterhorn (Webb & Gornall, 1989) and in the French Alps (Chas et al., 2006). This high-altitude record holder despite its high mountain locations and possible isolation shows considerable variation in flower colour and also produces the hybrid S. X kochii with S. oppositifolia (Fig. 10.4d).

Until the discovery of Saxifraga biflora on the Dom du Mischabel, the glacier buttercup Ranunculus glacialis was considered the highest growing European alpine species at 4270 m on the Finsterahorn. The glacier buttercup still retains the record for the highest growing flowering plant in Scandinavia, reaching 2370 m at Galdh0piggen, the highest mountain in Norway and in northern Europe (2469 m a.s.l. - 62° N). Galdh0piggen is also the site of the highest occurrence of Saxifraga oppositifolia in northern Europe (2350 m).

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