Temperate forests can be divided into deciduous forests, rainforests, and evergreen
forests. Deciduous trees drop their leaves as an adaptation to winter. Leaves being
delicate structures are likely to be damaged by freezing. Thus, nutrients are with-
drawn from the leaf and stored in the roots. The dead leaf is then shed. Because trees
need to regrow their leaves in spring they require a growing season of 4 – 6 months
with moderate summer rainfall and mild winters. They avoid the extremes of the wet
maritime and cold continental climates. These forests are found mostly in the
mid-latitudes of the northern hemisphere, particularly in western Europe, eastern North
America, and eastern Asia. There is a large variety of tree species with oak (Quercus),
beech (Fagus), maple (Acer), and elm (Ulmus) being common. Forests of western
Europe are not as rich in tree species because of extinctions during the last ice age.
Small mammals such as voles (Microtus), mice (Clethrionomys), and shrews
(Sorex) are numerous although with relatively few species. Large mammals are
represented by deer (Odocoileus, Cervus) and bison (Bison). The majority of the insec-
tivorous bird species, such as thrushes (Turdus) and old and new world warblers
(Phyloscopus, Dendroica), migrate to the tropics or southern hemisphere.
Temperate rainforests occur along the western coasts of North America, Chile, New
Zealand, and southern Australia, in maritime climates with high year-round rainfall.
They are known for their large trees (60–90 m high) such as redwoods (Sequoia
sempervirens) in California, Douglas fir (Pseudotsuga douglasii) in British Columbia,
eucalypts (Eucalyptus regnans) in Australia, and podocarps (Podocarpus) in New Zealand.
Diversity is often low for both plant and animal species. Large vines, lianes, palms,
and epiphytes are rare, but tree ferns in the southern hemisphere are common.
Temperate evergreen forests vary around the world. In this biome are included the
dry sclerophyll forests of eastern Australia dominated by Eucalyptusspecies with their
tough, elongated leaves; the dry pine forests of western North America including
Monterey (Pinus radiata) and ponderosa pine (P. ponderosa); and the dry forests of
southeast Asia. Canopies are open and the understory vegetation is sparse and often
adapted to dry conditions. Evergreen forests in New Zealand are quite different for
they occur in wet regions. Although close to Australia, these forests must have been
separated by continental drift before the Australian flora developed for there are
no eucalypts or acacias. The forests are dominated by evergreen conifers, notably
the kauri (Agathis), in the warmer north, and several species of Podocarpusand
Dacrydium in the south. There are five evergreen species of southern beech
(Nothofagus). New Zealand forests are noted for their endemic birds and the absence
of indigenous terrestrial mammals.Daily temperatures in tropical forests remain similar year round (24 –25°C), and day
length varies less than an hour. Seasons are determined by rainfall, there being some
months with less rain than others – 100 mm of rain is a dry month. In Malaysia,
Indonesia, and some parts of the Amazon basin (Rio Negro) all months have more
than 200 mm of rain, some receiving over 450 mm. In Africa and India there is a
short dry season. High temperatures in these forests cause high transpiration rates,
and plants have adaptations to overcome water loss through thickening of the
cuticle, producing leathery leaves. Examples are the rubber tree (Ficus elastica) and
Philodendron. Leaves in the shade are large; those in the light are smaller.
In contrast to the relative paucity of species in temperate forests there is a high
diversity of plants and animals in tropical rainforests. The most extensive rainforestBIOMES 13
2.2.2Temperate
forest
2.2.3Tropical forest