Geography Reference
In-Depth Information
glacialis,
in the Swiss Alps at 4,505 m (14,780 ft) (Körner 2011), and
R. grahami,
above
the permanent snowline at 2,900 m (9,600 ft) in the New Zealand Alps (Billings and
Mooney 1968). Ecological equivalents to these buttercups are the highest occurring
vascular plants in the world, growing at approximately 6,400 m (20,100 ft) in the Him-
alaya.
Characteristics and Adaptations of Alpine Plants
The primary adaptations of alpine plants include their ability to survive low temper-
atures, short growing seasons, low nutrient availability, and surface instability. Conse-
quently, alpine plant communities may exhibit higher levels of
facilitation
(the amelior-
ation of extreme environmental conditions by neighboring plants) (but see Dullinger et
al. 2007) and experience less resource competition than that experienced by plants in
more moderate environments (Welden 1985; Choler et al. 2001; Callaway et al. 2002).
Alpine plants exhibit many kinds of morphological, physiological, and ecological adapt-
ations to extreme environmental conditions; only the most important are summarized
here (Table 7.2).
LOW GROWTH FORM
One of the most striking characteristics of alpine plants is their low stature, which al-
lows them to grow in more favorable microclimates. Wind is greatly diminished near
the ground, resulting in less physical and transpirational stress. Temperatures are also
higher near the surface because of the absorption and reradiation of solar radiation, and
lower diffusion rates occur under the lower wind regime. An extreme example of differ-
ences between surface and air temperatures (30°C) occurs among the dense alpine car-
pets of azalea (
Loiseleuria procumbens
) in the Alps, where maximum canopy temperat-
ures (47.1°C) combined with high canopy humidity (RH = 87 percent) create near-trop-
ical microclimate conditions (Cernusca 1976). High temperature tolerance also varies
by species, and is related to both growth form and habitat-related moisture availability
(Buchner and Neuner 2003; Larcher et al. 2010). Similar to krummholz trees, the low
growth form of alpine plants ensures that they remain snow-covered during the winter
and the early growing season, when lethal frost can kill flowers (Inouye 2008) or en-
tire plants during cold spells when temperatures drop below −5 to −8°C (Larcher et al.
2010).
A notable exception to the dominance of low growth forms in alpine environments is
the giant rosette form characteristic of some plants in tropical mountains. These plants
have a candle-like form that reaches heights of several meters. They include the gi-
ant
Senecios
and
Lobelias
of the East African volcanoes and convergent growth forms
of
Espeletia
and
Lupinus
in the páramos of South America. The silversword (
Argyrox-
iphium sandwicense
) has a similar form and grows at high elevations in Hawaii (Troll
1958). Since tropical mountain environments allow metabolic processes to be carried
out throughout the year, the principal adaptations of these large columnar plants are to
protect the buds from nightly frost (Beck et al. 1982). They do this by developing large,
woolly leaves that curve inward at night and cover the buds, by developing corky cov-
erings, and by secreting liquid over the buds at critical times to prevent freezing (Beck
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