Temperate grasslands are similar to the tropical savannas in that they support peren-
nial grasses and are often maintained by fire. They are seasonal in both precipita-
tion (rain or snow) and temperature. They occur in dry climates in the centers of
the North American and Asian continents. In South America we see this vegetation
as the pampas of Argentina. Temperate grasslands experience cold winters with low
snowfall, spring rains, and a summer drought. Like tropical savannas they support
large herds of ungulates – bison and pronghorn (Antilocapra) on the American prairies,
saiga (Saiga) and horses on the Asian steppes – and carnivores such as wolves (Canis
lupus). Nonetheless the number of species is low. Birds are represented by larks,
pipits, buntings, grouse, buzzards (Buteo), and falcons.Arctic tundras occur north of the tree line in both North America and Eurasia. There
is a maximum of 188 days with mean temperature above 0°C but sometimes as few
as 55 days. The growing season spans the four summer months and is determined
locally by when the snow melts. Exposed areas have longer growth whereas those
under snow drifts have shorter seasons, and so a mosaic of vegetation is maintained.
Plant communities consist of a complex mixture of sedges, grasses, lichens, mosses,
and dwarf shrubs.
In the Arctic, soils are frozen in permafrost except for a shallow layer at the
surface which thaws in summer. Lemmings (Lemmus) feed on the vegetation year
round, being protected under the snow in winter. Geese nest in large numbers and
impose a heavy grazing impact in summer. Ptarmigan (Lagopus) are another abun-
dant bird group. Because of the permafrost the ground snow does not drain easily
in the summer and much of the tundra is swampy; these swamps provide ideal
breeding grounds for mosquitos, which form dense swarms in late summer. This
abundance of insects, combined with the almost constant daylight, provides good
breeding conditions for insectivorous birds – many shorebirds (plovers, sandpipers)
and passerines (e.g. snow bunting, Plectrophenax nivalis) migrate to this biome to
breed. Large mammals include muskoxen (Ovibos moschatus) and caribou (Rangifer
tarandus); small mammals such as arctic hare (Lepus arcticus) are sometimes numer-
ous, and wolves, arctic foxes (Alopex lagopus), and snowy owls (Nyctea scandiaca)
are common predators.In contrast to the tundra where precipitation is low and drainage poor, many alpine
areas have high precipitation, good drainage, and a high degree of fragmentation. In
temperate regions this leads to relatively high growth. In tropical regions tempera-
ture varies considerably during the day and forces special adaptations by plants.
Alpine meadows have a similar vegetation structure to that of the tundra but because
they are confined to mountain tops they are often found in small scattered patches.
Fewer bird and mammal species use these areas for breeding in comparison to the
tundra. In North America the characteristic mammals are marmots (Marmota), pikas
(Ochotona, a small lagomorph), and voles (Microtus) instead of lemmings. Elk
(Cervus elaphus), moose (Alces alces), caribou (Rangifer tarandus), and bears (Ursus)
use the meadows in summer. In Asia the Himalayan alpine zone is the center of
evolutionary radiation for the goats and sheep. These species form the prey of snow
leopard (Panthera uncia). Pikas have also diversified here.
Alpine meadows on the tropical mountains of Africa produce some extraordinary
adaptations in the vegetation. The weather is extreme: it freezes every night and becomes16 Chapter 2
2.5.2Temperate
grasslands
2.5.3Tundra
2.5.4Alpine