Geography Reference
In-Depth Information
1994). The stem sheath, consisting of woolly and hairy leaves, also helps protect them
from intense sunlight during the day (Hedberg 1965).
PERENNIALS
Most (98 percent) alpine plants in mid- to high latitudes are perennials, because of
their greater energy efficiency during the cool, brief growing season (Billings and
Mooney 1968). Whereas annual plants need to complete their entire life cycle (germin-
ate, flower, and fruit) during the short growing season, perennial plants avoid germin-
ation and initial growth processes and begin to metabolize quickly once conditions per-
mit. The lack of early life cycle stages among perennials presents the further advant-
age of being more hardy and resistant to the vagaries of the environment than young
and immature annual plants. Another adaptation that allows perennials to complete
their life cycle rapidly is the development of preformed shoots and flower buds (Billings
1974a; Moser et al. 1997). Many of these plants are also evergreen, thus eliminating
the need to grow new leaves before they begin to photosynthesize during the growing
season and creating additional biomass for energy reserves.
Tundra plants develop relatively large and extensive root or rhizomatous systems,
with two to six times more biomass below the ground than above it (Daubenmire 1941;
Billings 1974a; Webber and May 1977; Fig. 7.12). In some plants, such as the sedge
Carex curvula in the Alps, root longevity can result in a below to above-ground bio-
mass ratio as high as 18:1 (Grabherr 1997), and these plants can persist for hundreds
to thousands of years (Grabherr et al. 1978; Steinger et al. 1996) as confirmed by DNA
fingerprinting that detected clone systems (De Witte et al. 2012). These rhizome-root
systems provide important food reserves in the form of carbohydrates and starches that
the plants draw from during their rapid initial growth in the spring. Large root systems
also enhance water uptake under dry alpine conditions. Moisture stress in many alpine
areas is further substantiated by the presence of several other plant adaptations, in-
cluding thick waxy leaves, corky bark, succulence, and high osmotic pressures, which
enable the roots to take up any available ground moisture (Tranquillini 1964).
TABLE 7.2
Global Growth Form Classification of Alpine Plants
Shrubs (Nanophanerophytes)—Woody Species 0.5 to 6m Height
Growth Form: Krummholz
Structure: Environmentally shaped (pheno-
types) multistemmed, prostrate forms of sub-
alpine trees
Key Traits: Wind-shaped trees requiring snow
protection of canopy to avoid cuticle damage
and desiccation
Distribution: Midlatitude and boreal moun-
tains
Example: Picea engelmannii , Rocky Moun-
tains
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