Temperate forest grows in regions that have a wide range of climates. In some, winters are cold and summers are cool; in others, the winter is relatively mild, and the summer heat rivals that in the tropics.
Where winters are cold, temperate forest trees are usually deciduous, shedding their leaves in winter and growing a new set in spring; in warmer regions, many trees keep their leaves all year. Although temperate forest does not have as many animal species as tropical forest, it is still among the richest wildlife habitats on land.
In the depths of winter, deciduous forest can seem gaunt and empty, and largely devoid of animal life, but as the days lengthen in spring, and buds begin to burst, the habitat becomes alive with birdsong and animals on the move.
This transformation is triggered by a sudden abundance of plant food — one that nourishes large numbers of both the plant- eating insects as well as the animals that feed on them. Many of these forest animals are permanent residents, but they also include migratory birds that fly in from distant parts of the world.
Compared with tropical forest, temperate deciduous forest has relatively few tree species: the maximum number — found in some of the forests of eastern North America — is several hundred, while tropical forest might contain several thousand. Nevertheless, temperate forest trees are powerhouses of life.
Large oak trees, for example, can produce over a quarter of a million leaves a year — enough to sustain the army of weevils, gall wasps, and moth caterpillars that feed rapidly in spring and early summer while the leaf crop is at its freshest and most nutritious. Like tropical forest, deciduous forest has a clear, vertically layered structure, but there are some important differences.
The trees are rarely more than 30 m (100 ft) tall, and the canopy layer is usually deep but open, allowing light to reach the understorey and encourage plant growth. Fallen leaves rot slowly in cool conditions, so deciduous forest has an unusually deep layer of leaf litter that insects, woodlice, and millipedes use as food and cover. This means that while many small animals live in the cracks and crevices in bark, the place that is richest in invertebrate life is not the trees but the ground.
In warm parts of the temperate world, many broadleaved trees are evergreen. Unlike trees of deciduous forest, which grow in spring and summer evergreens grow in winter and spring, when temperatures are low but not cold, and when water is readily available.
Described by botanists as sclerophyllous (meaning hard-leaved) forest, this habitat is found in several widely scattered regions of the world, including parts of California and western South America, the Mediterranean region in Europe, and large areas of eastern and southwestern Australia. In some of these places, the forest is low- growing, but in Australia, where eucalyptus is the dominant species, it includes the tallest broadleaved trees in the world. Temperate evergreen trees usually have open crowns, which means that the vertical layers are often less pronounced than they are in forests in cooler regions, and plenty of light is able to reach the forest floor. As a result, these forests are rich in ground-based wildlife and warmth—loving animals -such as lizards and butterflies.
Which are usually associated with higher levels — can often be seen sunbathing on the floor. The open structure also makes it easy for birds, such as kookaburras and other forest kingfishers and rollers to swoop down on animals moving about on the ground.
The air in evergreen forest often smells pleasantly aromatic because most of the leaves are filled with pungent oils. These oils help to stop the leaves from drying out, and they also protect them from animals. They are a highly effective deterrent, as relatively few animals – apart from specialists such as the koala — include these leaves in their diet.
As a habitat, deciduous temperate forest — the kind of forest found across much of the northern hemisphere — has one very useful feature. The trees that grow in it, such as oak and beech, produce leaves that are designed to last for just one growing season. As a result these leaves are usually thin and easy to eat, which is why vast numbers of insects feast on them from the moment they begin to appear in spring.
This sudden explosion of insect life attracts an army of highly specialized avian predators. In Europe, Northern Asia, and North America, dozens of warbler species migrate north as the buds open.
These birds have extremely acute eyesight, enabling them to scour leaves for the tiniest grubs and caterpillars, which they then pick up with their tweezer-like beaks. Other birds, including tree-creepers, woodpeckers, and nuthatches, concentrate on the bark, seeking out and pecking at the tiny animals hidden among the crevices. By midsummer, leaves stop growing and animal feeding behavior changes. Most temperate trees are pollinated by wind, which means that they do not produce enticing nectar-rich flowers.
However, these trees do produce large crops of nuts and other seeds, which are extremely important foods for animals because, unlike leaves, they can be stored away and used when other food is scarce. Food storage, or “caching”, is practiced by many forest birds and mammals. Jays bury acorns in the ground, while acorn woodpeckers store them in trees. Squirrels bury seeds of all kinds, and red foxes bury anything that is even faintly edible, from half-eaten remains to food wrappers and discarded shoes.
Some animals locate their stores by scent, but most are very good at pinpointing them by memory alone, finding and digging up their food even when it is covered by snow. Seed-caching has an important impact on forest ecology. Although animals that bury seeds have good memories, some of what they hide is always forgotten about.
This means that provided the seeds are not discovered by rodents or other animals, they remain effectively planted and ready to germinate, helping the forests trees to reproduce.
In autumn, many insect- eating birds migrate to warmer climes, leaving the forest remaining animals to face the winter cold. Animals that store food can remain active through out this difficult time of year, but others use a very different survival strategy: they hibernate, living on the fat reserves they have built up during the summer months.
How long and how deeply an animal hibernates depends on where it lives. In the forests of northwest Europe, hedgehogs may hibernate tor up to 6 months, whereas further south their winter sleep is much shorter in eastern North America, woodchucks or groundhogs — typically hibernate from October to February: their wanderings early in the year are a traditional sign that spring is not far off.
Some hibernating animals, such as the common dormouse hardly ever interrupt their winter break even if they are picked nest and into another, but forest hibernators have to be careful not to do this too often: activity uses up their bodily food reserves, and it their for puts them at risk of running out before the winter is truly over. Many insects also hibernate, often hidden under bark; but in some species, the adults die out, leaving behind tough, over wintering eggs that will hatch in spring.
While monkeys and gibbons are the most impressive climbers in tropical forest. squirrels are the experts in temperateftorest. Unlike many climbing mammals. they can run head-first down tree trunks. as well as up them. by hooking their long. curved hind claws into bark. Squirrels have excellent eyesight. and they instinctively scuttle to the back of a tree if they spot a potential predator — a simple behaviour that makes them difficult to catch. Temperate forest is inhabited by gliding rodents. and also in Australia — by gliding marsupials. But for precise manoeouvring among trees. owls and birds of prey are unrivalled. Unlike their relatives in open habitats, most ot these ariel hunters have relatiely short broad wings that enabte them to twist and turn effectively. A prime example ot this adaptation to woodland life is the Eurasian sparrowhawk: rather than soaring and then swooping.itt speeds among trees and along hedgerows – sometimes only a metre or so above ground — ambushing small birds in mid-air and carrying them away in its talons. Temperate forest provides ground-dwelling animals with lots of cover. As a result. small mammals. such as voles and shrews. abound on the forest floor. To avoid being seen as they move about. these animals often use runways partly covered by grass or fallen leaves. Voles use a combination of vision. smell. and touch to find their way along these runs. but shrews. which have yery poor eyesight navigate partly by emitting high pitched pulses of sound. These sigals bounce back from near by objects in the same way as those sent out by a bat’s sonar.
LIVING IN LEAF LITTER
The leaf litter in temperate forest is one of the worlds richest animal micro-habitats. This deep layer of decomposing matter harbours vertebrates. Including mammals and salamanders, but its principal inhabitants invertebrates that feed on leaf fragments on fungi and bacteria, or on each other.
Some of these animlas — such as centipedes and woodlice — are large enough to be easily seen, but many others are microscopic animals that live deep in leaf litter exist in total darkness, so most of them rely on their sense of touch to find food. This is especially true of predetors: centipedes locate their pray with long antennae while tiny pseudoscorpions use the sensory hairs that cover their pincers.
Like true scorpions, pseudoscorpions are venomous: but they are so small that they pose no threat to anything much bigger than themselves. This is fortunate because in just a few square meters of leaf litter their numbers can run into millions.
Dead leaves are a useful screen, hiding leaf-litter dwellers from other animals foraging on the forest floor. However, it is not totally secure. Some temperate forest birds particularly thrushes, pick up leaves and toss them aside. snapping up leaf-litter animals as they try to rush away from the light.