grasslands, semi-desert scrub, and deserts. We include one group of marine biomes.
Walter (1973) provides more detailed descriptions.Taigain Eurasia or boreal forestin North America starts where 10°C mean daily
temperature is exceeded for more than 30 days per year. Tundra takes over where
this temperature is exceeded for less than 30 days. The boreal forest is dominated
by several species of conifer of the genera Pinus(pine), Picea(spruce), Abies(fir),
and Larix(larch), although only white spruce (Picea glauca) spans the whole of North
America. Eastern Asia also has many species of conifer, but, in contrast, only two
species, Norway spruce (Picea abies) and Scots pine (Pinus sylvestris), predominate
in Europe.
In dense boreal forest the shrub layer is almost absent and mosses dominate the
herb layer. In openings of the forest, and in wetter areas where trees are absent, there
is a sparse shrub layer of willows (Salix), birches (Betula), and alders (Alnus). Soils
are acid, low in nutrients, and have a thick humus layer that takes a long time to
decompose.
Boreal forest is the main habitat of the snowshoe hares (Lepus americanus) and
their main predators the lynx (Lynx canadensis), great horned owls (Bubo virginianus),
and goshawks (Accipiter gentilis). Among other birds, ravens, swallows, chickadees,
woodpeckers, and forest grouse are common. During the Pleistocene this was also
the habitat for browsing mastodons (Mammut americanum), woolly rhino (Coelodonta
antiguilatis), and giant ground sloths (Megalonyx).12 Chapter 2
–15–10–5051015202530
50 100 150 200 250 300 350 400 450
Mean annual precipitation (cm)Mean annual temperature (°C)TundraBoreal forestTROPICALArctic-alpineCold temperateWarm temperateTropicalPrairie shrublandWoodlandForestSemi-desert / desertSavanna Forest RainforestRainforestWoodlandTEMPERATE0Fig. 2.1World biome
types in relation to
rainfall and temperature.
(After Whittaker 1975.)
2.2 Forest biomes
2.2.1Boreal forest