Mountain Vegetation - Mountain Geography: Physical and Human Dimensions - page 373

production in midlatitude alpine tundra has been measured to average 0.20 to 0.60
g/m 2 /day (0.0007 to 0.002 oz/ft 2 /day) over the entire year, or 1 to 3 g/m 2 /day (0.035 to
0.105 oz/ft 2 /year) during the 30-70 day growing season (Bliss 1962). Since root biomass
is commonly two to six times greater than shoot biomass, estimates of total productivity
would be approximately three times greater (Billings and Mooney 1968; Webber 1974;
Webber and May 1977). These annual productivity rates are far less than for temperate
environments and similar to those found in desert environments. Daily growing season
productivity rates, however, show that alpine tundra productivity exceeds that found
in many temperate environments (Bliss 1962, 1966; Scott and Billings 1964; Bliss and
Mark 1974; Webber 1974).
The key to the relatively high productivity rates of alpine plants is their adaptation
to low temperatures and their ability to metabolize—at low rates—during subfreezing
temperatures. This allows plant growth throughout the short growing season. During
this period, photosynthates, the chemical products of photosynthesis, are initially used
to produce plant biomass or later stored as energy reserves. This temporal allocation of
resources is illustrated in the Alps by the high daily growth rates of Carex curvula dur-
ing the first half of the growing season, followed by subsequent storage of starch and
lipids in rhizomes (Grabherr et al. 1978).
Some alpine plants can also photosynthesize at temperatures as low as −6°C (21°F)
(Billings 1974a), albeit at greatly diminished rates. Other alpine plants appear capable
of withstanding frost conditions throughout their life cycle (Tsukaya and Tsuge 2001).
While these characteristics improve the probability of survival and successful repro-
duction for some alpine plants, photosynthetic gains during frost periods are generally
minimal, and frost damage during flowering often results in high stem, leaf, and flower
mortality (e.g., Inouye 2008; Larcher et al. 2010).
Other adaptations of alpine plants include their rapid metabolic rates and their abil-
ity to use food reserves stored in old leaves and large root systems during initial spring
growth. These reserves can then be replenished later in the season. Research on the
dwarf shrub Loiseleuria, however, suggests that only a small proportion of photosyn-
thates may be mobilized (Larcher 1977) and that unused reserves stored in branches
and the evergreen leaves are shed after 3-6 years and lost to the system (Grabherr et
al. 1978).
In general, alpine plant productivity and biomass accumulation are higher in areas
of mild climates than in cold climates (Kikvidzek et al. 2005). Growth rates of alpine
plants are also influenced by the length of the growing season, as determined both by
seasonal changes in solar radiation and temperature and by the local persistence of
snow-pack. In areas of early spring snowmelt, plants can develop relatively slowly, tak-
ing the entire growing season for the various phenological processes. Conversely, in
areas of late snowmelt, growth processes are compressed and the entire life cycle must
be completed within a few weeks (Billings and Bliss 1959; Rochow 1969; Körner 2003).
Spatially, plant biomass, productivity, and nitrogen use increase over alpine topograph-
ic sequences from dry to wet meadows, where snow contributes seasonal moisture but
does not shorten the growing season (Fisk et al. 1998).
Summary