Oak Woodlands in Winter
Winter is sometimes called the dead season. But as you walk through the silent woods in January, do not be deceived into thinking that nothing is alive. Winter is a resting season, and life’s chemical processes, although slowed down, still go on.
Think of the common woodland wild. If such plants can be said to have a dead season, it is summer, rather than winter. When certain species show the least life. When lesser celandines and wood anemones have finished blooming in spring they quickly vanish – flowers, leaves and stems all rot away, and the carpets of bluebells, so colourful, lush and sappy in May, have quite disappeared by August. Yet these plants, and others, are all actively growing again, above or below ground, by the end of the year; and already in January, if the season is mild enough, celandines, anemones and primroses may be showing their first flowers.
Not all our winters are mild, and plants and animals have to be able to take this fact into account. As they evolved over millions of years one of their continual and pressing requirements has been to develop a method of getting safely through the coldest winter. A common solution to this problem is to take refuge in the winter woods. To see why, you need only take a walk some bitter winter’s day. When you have to struggle against an icy north-east gale along a frozen field path that leads you to a wood, especially one with plenty of undergrowth. Once well in among the trees you are in a different world – less cold, sheltered and altogether more habitable. A woodland has a climate of its own; and the bigger the wood the more sheltered are its depths where tender species can escape the worst frosts and drying winds.
To tell the complete story of oakwoods in winter it is necessary to begin in the autumn, when the leaves are falling, for they play a large part in the life of the wood at all seasons. They lie thick on the ground for a few weeks, but in the dampness of early winter they are attacked by moulds and fungi and gradually decay, adding their substance to the leafmould.
So the woodlandis formed, not only of leaves but also of twigs, branches and fallen trunks, along with all the dead plants, dead animals and animal droppings that eventually fall to the ground. This soil and its leafmould cover become a deep and fertile layer, providing food and a habitat for countless forms of life, especially in winter.
As well as leaves there are acorns to help form the woodland soil. In some years they are produced in such multitudes that several hundred may lie in a single square yard below an oak. Then what happens? Few of them are left to lie. They are quickly found and either eaten or hidden by wood-pigeons, jays, rooks, pheasants, deer, squirrels, mice, voles and insects. Most of the rest are attacked by fungi. The result is that only a very few of these millions of acorns ever germinate.
Some midwinter wild flowers disappear in the summer time, but not all woodland plants are so ephemeral. There is wood-sorrel, for example, whose ground-covering carpets of clover-like leaves are green the whole year round and often climb decoratively over stumps and fallen trunks. Then there are mosses and liverworts. Because they flourish in cool dampness, winter is their best season; they can be enormously abundant, covering ground, tree trunks and high branches in an ever fresh, bright-green mantle. Hardy against frosts, many of them choose winter as the time to produce their fruits, which often stand up elegantly on slender stalks.
Many ferns, too, are evergreen and remain standing in the shelter of the winter woods; and those that die down, bracken for example. Provide a thick warm shelter for numerous small animals. On tree trunks, branches and twigs many kinds of lichens occur, some bushy, some leafy and some formed into flat crusts. All are hardy and are not troubled in the least by winter’s cold.
Perhaps you have examined leaf mould in summer and found it crawling with invertebrates – all the myriads of mites, millipedes, centipedes, earthworms, beetles and other creatures. They are all there in January, too, some hibernating, some simply hiding, ready to creep out and seek food during mild spells.
Similar communities live up in the trees – woodlice, false scorpions, spiders and many others which exploit the warm damp micro-climates to be found behind the sheets of loose bark or in decaying holes. There are also legions of beetle larvae burrowing away all winter into the wood of trees. Some moth larvae are found, too, like those of the clear-wings: or the big, red-brown caterpillars of the goat moth, which bore large holes into oaks and other trees.
Go into the wood some mild winter night, preferably in the week or two before Christmas, and you’ll find moths in plenty: these are winter moths and mottled umbers. They flutter round your torch, or you can see them crawling up the trunks of the oaks. The ones you see flying are all males which have just emerged from their pupae in the earth, and their one aim is to find a female with whom to mate. The female’s story is just as simply told: she appears from the ground and crawls up an oak – lacking wings, she cannot fly. During her ascent she mates with one of the waiting males, then goes on climbing to some high twig, where she lays her eggs near the tightly closed leaf buds.
The scores of other oakwood moths, as well as the various butterflies, have each in their fashion evolved a way of coping with the cold and hunger of winter. Most have opted for dormancy, either as eggs or pupae. But in October or November the brimstone butterfly hides away among ivy or other green cover in adult form, and is ready to fly again before winter is over if a sufficiently warm day occurs. The footman moths, on the other hand, pass the winter as active caterpillars, eating leafy lichens on the oaks during spells of milder weather.
Only a few vertebrate animals have chosen hibernation as their means of survival. Toads, grass snakes and adders come into the woods in fair numbers to get out of the cold, squeezing into holes in the ground. Hedgehogs make elaborate weatherproof nests of dry leaves, grasses, mosses and bracken in a sheltered spot and are snug the winter through. Dormice also sleep the cold weather away in mossy nests.
Travellers and residents
Hibernation is an escape route the birds do not take. Instead, many of them migrate: warblers. Redstarts and flycatchers depart south in the later weeks of summer. Soon afterwards come the first arrivals from cold northern Europe: woodcock, redwings, fieldfares and some of the finches from the Arctic.
Some of the woodland birds (residents or visitors) are solitary species – woodpigeon, Jay and woodcock for example. Others move around the woods all day in parties of mixed species. Such a flock may afford a measure of safety in that a predator can be detected and warning given to the whole party, whereas a solitary bird must rely solely on its own watchfulness. As you follow a woodland path in winter the scene may seem silent and lifeless until you meet a bird party. Then you may see scores of tits. Nuthatches, tree creepers and others fluttering about and calling frequently as they pass through the trees. They feed as they go, each species taking its chosen types of food and so not competing with the others. Then the whole flock moves on, leaving you again in the quiet of the woods.