Biology Reference
In-Depth Information
Figure 2.2
Vegetation diagram of North America north of Mexico. Some vegetation types,
such as beach/strand/dune, freshwater herbaceous bog/marsh/swamp, aquatic, and alpine
tundra, are too limited in extent to show on the map. Used with permission from Oxford
University Press, Oxford.
lated clusters of
Picea
(spruce),
Alnus
,
Betula
, and
Salix
(dwarf alder, birch,
and willow), and a herbaceous cover of lichens, mosses, grasses, sedges,
and forbs (fi g. 2.3; see table 1.1 above as a guide to the illustrations of plant
formations). The tundra presently covers ice-free areas of the Arctic region
and extends southward only to about 60°N along the west coast because of
the warm Japan Current, while along the east coast it extends as far south
as 55°N because of the cold Labrador Current. Inland, the southern bound-
ary is defi ned by the limits of permafrost. The growing season is only some
six to twenty-four weeks, frequent winds of 65 km/hr (40 mi/hr) or more
may last for days, and there are twenty-four hours of near darkness for six
months of the year. The lowest temperature ever recorded in North America
