Conifers are the world’s toughest trees. Their small, needle-shaped leaves can withstand extreme cold and are impervious to strong sunshine and wind, and their relatively narrow, upright habit enables them to grow closely together to form dense, sheltered forest.
As a result, conifers thrive where few broadleaved trees can survive, such as the far north and in mountain ranges. They also flourish in places that have very heavy rainfall. In such areas they form temperate rain-forest, home to some of the largest trees in the world.
Named after Boreas, the Greek god of the north wind, boreal forest, or taiga is the largest continuous expanse of forest on earth. It covers about 15 million square km (6 million square miles) and stretches in an almost unbroken belt across the far north, often reaching deep into the Arctic.
In some places, the belt is over 1,600 km (1,000 miles) Wide. Across the boreal forest belt as a whole, winter temperatures routinely drop below -25°C (430 F), but in some of the coldest regions, such as northeast Siberia, temperatures can fall below -45 C°(-49° F). Summers in boreal forest are brief but can be warm.
Compared with the types of forest that occur at lower latitudes, boreal forest has only a handful of tree species and therefore provides only a limited variety of food for herbivores. Plant diversity is also restricted both by the amount of light that can reach the forest floor and by the high acidity of pine needles. Even in summer, the interior of the forest is often dark, with a thick layer of dead needles carpeting the floor. Fungi thrive in these conditions, but the only forest-floor plants that live here are the ones that can tolerate low light levels and acidic soil conditions.
Apart from insects, few animals can digest conifer leaves or wood, so most plant-eaters concentrate on seeds, buds, and bark, or on berries from low-growing shrubs. However, what this habitat lacks in variety, it more than makes up for in quantity, especially as there is relatively little competition for food. This is one of the reasons why many boreal forest animals, from birds to bears, have far more extensive ranges than species that live in warmer parts of the world.
The world’s largest areas of rain forest are found in the tropics, but rain forest also exists in parts of the temperate world, it grows where west-facing mountains intercept moist air blowing in from the sea and, unlike boreal forest it experiences relatively mild temperatures all year round.
Compared with boreal forest, temperate rain-forest is a rare habitat, occurring in a few widely separated areas. In the southern hemisphere, it is found in the South island of New Zealand, and in parts of southern Chile. In both of these places, most rain forest trees are broadleaved species, but in Americas Pacific northwest — where the largest temperate rainforest in the world can be found — the trees are almost entirely conifers. Some are over 75 m (nearly 250 ft) high, and more than 500 years old.
This kind of coniferous forest looks unlike any other. On the ground , and in the understorey, every surface is draped with ferns or waterlogged moss. Densely packed trunks, some over 3 m (9 3/4 ft) across, rise up to the canopy high overhead, where the sky is always laden with rain. Temperate rainforest supports many animals that are found in coniferous forest all over the world, but it has some additional features that set it apart: the mild, damp conditions.
Which make it a haven for slugs and salamanders, and the immense amount of fallen timber which creates opportunities for insects that feed on dead Wood. In its natural state, the forest teems with mammals, as well as with owls and other birds that need large old trees as nest sites. Unfortunately, these trees are in great demand by the timber industry and, as a result untouched temperate rainforest is increasingly rare.
LIFE IN CONIFEROUS FOREST
For animals and trees alike, life in boreal forest is dominated by the need to survive long and extremely cold winters. Animals that remain active in winter, such as wolves, need a constant supply of food simply to avoid freezing.
Conifers are difficult to exploit for food, which means that animals that rely on them have developed some highly specialized physical and behavioral characteristics.
Compared with many broadleaved trees, conifers are well protected against attack. In addition to tough leaves, they often have only resins that make both their leaves and their wood difficult to digest.
Furthermore, if the sapwood is injured this resin oozes out and traps insects and spiders as effectively as glue. Despite these defenses, some animals manage to live entirety on coniferous trees. Among the most successful are sawfly larvae.
These caterpillar like grubs bore deep inside the trunks, leaving cylindrical tunnels in the wood. They do not eat the Wood itself: instead they feed on a fungus that grows on the walls of the tunnels they have built. Female sawflies carry small amounts of this fungus with them when they emerge as adults, and they infect new trees when they lay their eggs, This kind of mutualistic partnership is vital to sawflies, but it is not entirely unique: in other habitats‘ particularly in the tropics. ants and termites also “cultivate” fungi as food.
Although Wood-boring grubs are safe from most predators, they are not immune from attack. Coniferous forest is the habitat of some of the world’s largest woodpeckers, which hammer their way into tree trunks to reach the grubs inside. Sawflies also face a threat from the ichneumon wasp, which drills through the wood with its long ovipositor to lay its eggs oh the sawfly larvae.
It is thought that the wasp locates the larvae by smell. When eggs hatch, the ichneumon grubs eat their host larvae alive. Some animals, such as the capercallie and North American porcupine, eat large quantities of conifer needles, but moth caterpillars are the leading leaf-eaters: as always in coniferous forest, the number of species involved is small but the damage they inflict can be vast. This is especially true of species such as the gypsy moth, which has been accidentally introduced to many parts of the world.
FINDING WINTER FOOD
Conifers do not have flowers, but they nevertheless produce seeds. For birds and small mammals, this seed crop is a valuable winter fuel. However‘accessing conifer seeds is not easy: they develop inside woody cones and the cones stay tightly closed until the seeds inside are mature.
Coniferous forest animals have developed a variety of ways of removing these seeds before the trees scatter them on the forest floor. Squirrels gnaw through the soft unripe cone while it is still attached to the branch, eating the seeds and drooping the remains of the cone on the ground below. Woodpeckers often take fallen cones and wedge them into tree holes or broken stumps, using these to hold the cone firm while they peck out all the seeds.
Crossbills are even more proficient: their beaks are uniquely adapted for dealing with cones, enabling them to extract the seeds with surgical precision. Compared with seeds, bark is a low-quality food but in winter it is vital to some species survival. Deer strip it away from the base of young saplings, while bank voles ad porcupines often climb trees to attack the bark higher up. Bark stripping often stunts a tree’s growth, and a severe attack can kill it.
COPING WITH COLD
Coniferous forest has its share of seasonal visitors: principally insect-eating birds that arrive in spring and then leave for the south once they have raised their young. But for the rest ot its animals, long winters are an inescapable fact of forest lite. Some species hibernate. but many remain active even during the coldest months. relying on their insulation for survival.
One group of forest animals, mustelids, have coats that are exceptionally well insulating. This group includes pine martens, wolverines, minks. and sables, all of thern agile hunters renowned tor their thick and luxurious fur. As with most “namrnals, their coats contain two ditterent kinds oi hair: long, outer guard hairs from the coat’s water-repellent surface while shorter, much denser, hairs – underfur – trap a layer of air close to the body, keeping the animal warm. Northern species all grow an extra-thick coat after their late-summer moult; and some species, such as the stoat ue this moult; and some species, such as the stoat, use this moult, to change colour, developing a white coat that provides better camouflag for the winter.
Keping warm is relatively easy for large mammals because thier body contain a large dtore of heat. But for the smallest warm-blooded inhabitants of coniferous forest, winter conditions, test their colid tolernce limits. Voles and other rodents can hide in burrows. but birds spend rnost of their lives in the open.
For Wrens and tits. which often weigh less than 10g (3/8oz). winter nights are a particularly dangerous time. With such minute bodies. their fuel reserves are tiny. and so they must make special provision if they are to stay aliye until dawn when the search for food can resume.
Some ot them rnake the most of what body heat they have by huddling together in tree holes. but a few. such as the Siberian tit. bed down in the snow. using it as an insulating material.
Since there are relatively few animal species in the northern coniferous forests, the lives of predators and prey are very closely linked.
During mild years, strong tree growth can trigger” a population explosion among small animals: as a result, the predators that feed on them begin to increase in number. These conditions never last for long though: as the plant-eaters begin to outstrip the food supply their numbers start to fall again and as the rate of the fall accelerates the predators soon follow suit. Despite the unpredictability of the northern climate, these ups and downs occur with surprising regularity.
In North America, fur trappers records dating back over a century provide some long-term evidence of population swings. For example, they show that the snowshoe hare population roughly follows a 10 year cycle. with 2 or 3 good years followed by a lengthy slump.
The Canadian lynx- one of the snowshoe hare’s main predators — follows the same pattern but with a one- or 2-year time-lag. Similar cycles involving lemmings and other small mammals take place in tundra while there is little that they can do to prevent this boom—and—bust pattern from occurring. Animals like the snowshoe hare are able to make a fairly fast recovery from a population slump by breeding quickly when conditions are favorable.