Geoscience Reference
In-Depth Information
Figure 2.14.
Distribution of Arctic polar desert (dark shading) and approximate
southern limit of tundra (bold line) (adapted from Charlier,
1969
, also see Webber,
1974
, courtesy of N. Saliman, NSIDC, Boulder, CO).
In the Low Arctic of both northern continents, vegetation covers 80-100 per-
cent of the surface. Shrubs are an important component, together with sedges and
grasses. There is variety in the vertical structure. Several species of alder, birch, and
willow in the tall shrub tundra reach 2-5 m height, whereas in low shrub tundra,
dwarf birch and dwarf willow are only 40-60 cm high. Where the canopy is more
open, heath and tussock species are widespread. At the southern margin of the Low
Arctic tundra, there is a forest-tundra transition or ecotone. Tree “islands” and gal-
lery forest are found along major watercourses such as the Mackenzie, Khatanga,
and Lena rivers, extending to 71°N to 72°N. The forest-tundra ecotone is some
50-100 km wide. This is a result of the effects on the forest limit of climatic fluctua-
tions over the past 4,000-5,000 years, and recurrent fires that destroy slow-growing
lichens and mosses (Nichols,
1976
; Elliott-Fisk,
1983
). South of the ecotone is the
boreal forest (or taiga, a Russian term).
As outlined in
Chapter 1
, in response to warming, the vegetation of the Arctic
is changing, including greening of the tundra (as assessed from satellite data) and
