prevalent in certain biomes. The following biome description is based mainly on
vegetation, the most noticeable landscape feature of each biome. The natural areas
of these biomes are given in the map, although there has been major anthropogenic
disturbance in boundaries and composition of most of them.
First, there are some land areas virtually uninhabited by life forms. These are
the permanent snow and ice areas found at high altitudes and, most expansively,
in Antarctica and Greenland.
Tundra is a low-energy biome related to high latitudes and altitudes. Corre-
sponding to tundra climate, the world’s largest extent of the tundra biome is found
fringing the Arctic Ocean. The growth of plants is slow because of low tempera-
tures and seasonally short/nonexistentsunlight periods. The landscape is domi-
nated by lichens, sedges, short grasses, and herbs that can withstand an
environment that is frozen much of the year. These plants are relatively simple
and the biome is not very diverse in plant and animal species.
Boreal forest (taiga) is found equatorward or at lower elevations than the tundra
biome. The forest is coincident with subarctic climates and is only extensive in the
Northern Hemisphere because of the lackof continental surfaces at accordant
latitudes in the Southern Hemisphere. Theboreal forest has a considerable cold
season making photosynthesis all but impossible except for the short, cool
summer. The typical forest species are evergreens like spruces and firs and decidu-
ous like birches and maples. Underlying soils tend to be acidic and infertile.
Temperate forest extensively occurred in the more humid portions of the middle
latitudes, but these areas have been heavily altered through deforestation and non-
native species introduction. The wetter portions of humid continental, humid sub-
tropical, and marine west coast climates were once dominated by the temperate for-
est. The temperate forest has a summer season with little moisture ortemperature
stress and a cold winter season (in some places snowy) precluding intensive
photosynthesis. The forest is dominated by large trees that vary in species mix
by location. The mix tends to be very biodiverse and encompass a large amount
of biomass. Usually, there is a forest canopy layer with understories of smaller
trees, bushes, and shade-tolerant plants. Most tree species are deciduous, but
there are notable areas of needleleaf evergreen dominance in the southeastern
and northwestern United States.
Temperate grasslands are areas dominated by grasses with a relatively few trees
relegated to watercourses. Temperategrasslandsare the vegetative response to
cold winters and warm/hot summers with evapotranspiration stress. Grasses store
energy in their root systems in preparation for winter and regenerate their above-
ground portions in the early warm season. They are quite conservative of moisture
and nutrients so that they present fertile soil when first tilled. Geographically, tem-
perate grasslands are widespread between humid areas of forest and arid areas of
Biomes 35