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Winter: frost, snow and darkness...

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The meteorologists tell that winter starts when the average temperature of day and night drops below zero and ends when the average temperature rises above this limit. In Kajaani district winter season lasts almost six months and in Lapland even seven months.

The weathers in autumn change all the time, winter comes and goes but near Christmas the winter takes over. Because seas and rivers are long ice-free there are often thaws in the early winter. Anyhow, years are not brothers with each others.

Especially in northern Finland winter is clearly longer than other seasons but not very special. The northern areas of Finland are typical snow forest climate areas. Statistically February is colder than January. The snow cover is thickest in March.

In February there are only 8 - 11 light hours. In the end of February, when the day is long enough, there are already first signs of spring: tits are singing and the owls are hooting. The fluctuation of day length is the most important time-signal to animals and plants.

The ground freezes in sand and gravelled areas till the depth of half meter and when it’s very cold and the snow cover is thin, over one meter. Also waters freezes deeper when there is less snow and when the snow comes late. In the mid of March the ice cover is widest: the northern part of the Gulf of Bothnia is normally frozen all the way to the Merenkurkku.

In the mid of February there are little promises of spring, the mid day sun may warm a bit. In March the day and the night are as long but the snow cover is thickest and the ice cover in the lakes strongest. During the day the snow often melts a bit but then it freezes again in the night, that’s how the crusted snow is formed. Snow melts also from the branches of trees and it seems like the greenness of coniferous trees increases while looking at them. A lot of litter falls from the trees, like branches, cones, seeds from spruces, pieces of bark.. First willow catkins appear, the trunks of young birches look reddish as if the blood started to circulate in them. And the great tit sings eagerly.

The living nature

The preparation for winter is long and complicated procedure for plants and animals. Only small part of the adaptation for winter is visible, most of it happens in the cells where biochemical changes increase the cold and dry tolerance of cells. At the same time plants have to stop or reduce some important processes that are happening during the summer, like assimilation or activity in animals. Still winter destroys a lot of life.

Along with the tolerance of coldness and dryness, tolerance of winter includes the idea of how to survive the snow cover or the near lack of it. In estimating the effects of the snow cover on animals, the abilities to move in the snow, to find shelter in the snow, to dig food from under the snow, and to adapt to food above the snow has to be taken into account.

Formozov (1946) has divided mammals and birds into three adaptation types. Moreover, the same classification has been used in clarifying the plants’ response to the snow cover. Some species of plants tolerate conditions with nearly no snow during the winter (e.g. in bare mountaintops) whereas some other plants demand the necessary snow cover in order to survive the coldness and/or dryness of winter.

1) Chionophiles i.e. those that are in favour of snow and benefit from the snow cover.
2) Chionophobes i.e. those that avoid snow and do not survive in snow conditions.
3) Chioneuphores that survive relatively well in snow, even though they do not have special structural adaptations.

Mid winter is very quiet in nature. And so grey that it’s hard to tell where the ground ends and sky starts. It’s like the time has stopped. Only snowflakes are falling quietly. Maybe wind sighs in the branches or trees make cracking noises (tissues are splitting). But nature is not dead - it just rests and tolerates at the same time.

Animals in winter

Not everyone is resting. When you stop for a moment in a forest you’ll see and hear tit flocks looking for food from the bark cracks (dormant insects and seeds of trees). They have collected food starting already in autumn. You can also hear woodpecker knocking: it has set a spruce cone in a little hole in a tree and eats the seeds. After some time there is a pile of cones under the tree, it is woodpecker’s ‘smithery’. In the snow there are tracks made by animals and there is a lot of action under the snow.

Even though it’s dark under the snow, it’s quite "warm" there, the temperature is near zero. Many insects and small mammals spend the winter in the ground under the snow. Temporarily - when it’s very cold - black grouse, hazel hen and willow ptarmigan sleep under snow in a hole (shelter).

Many animals that stay here for winter, especially poikilothermic ones, and almost all plants (they are poikilothermic, too) are in a dormancy during the mid winter. Some species have very deep dormancy but there are species that may wake up for a while when it’s milder.

Poikilothermic animals, for example insects, snails and worms, are of course in a real dormancy because they can’t adjust their body temperature. They overwinter in a place where there aren’t threats to get eaten by a bird or small mammal. Many northern insects and plants need to experience some kind of a winter before they develop more. There aren’t many insects that overwinter as adults, larva or pupa are common forms to overwinter. Many insects overwinter as eggs, too. Some beetles and butterflies overwinter as adults.

It gets quiet in waters, too: insects, snails and worms dig in to bottom silt or get in to ground and dig themselves there for example in to detritus. Many small organisms overwinter as dormant spores or as hard-shelled eggs or surround themselves with hard shells. That’s how they tolerate both coldness and dryness, which are the main threats during winter. Also fishes, reptiles and amphibians are poikilothermic. Many fish species are very slow during winter, amphibians and reptiles doesn’t move at all. Amphibians spend their winter in a bottom mud of puddles, snakes gather in to ground holes that are one or two meters deep. There can be hundreds of snakes in one hole. Amphibians can move a bit when it warms a bit and they wake up from their dormancy quite quickly, reptiles need more warmth.

Some mammals, even though they are quite homeothermic during summer, have dormancy. For example bear, hedgehog, badger and bats. Bear and badger are homeothermic during winter, too and they wake up very easily. The cubs of bear are born in the mid winter and they weight about quarter of a kilo when an adult weights about 100 kilos.

In Finland, there are 40-50 species of winter birds that can be seen regularly. There is about a hundred species of temporary overwintering birds. During the winter, our avifauna decreases further; birds die or transfer elsewhere.

A great problem for many winter active animals that stay here in the north over the winter is how to find enough nourishment. Some gather nourishment in store already during the late summer and autumn. In addition to the supplies in the ground that can be used in the winter, some animals (birds, mammals) gather fat in their bodies as a reserve nutrition, among other things between internal organs and under the skin (e.g. neck and stomach). The weight of such animals is at its biggest in the autumn but decreases, even rapidly, during the winter.

Those mammals that spend the winter in hibernation or in torpor (e.g. badger and bear) have the greatest need for fat reserves. Furthermore, many winter active mammals, e.g. reindeer, gather fat in the autumn. Northern small mammals gather so-called brown fat, which generates heat very effectively. In the winter, 10% of the weight of the smallest mammals, e.g. shrews, may consist of brown fat. Even the bigger mammals have this kind of fat to some extent during the winter.

Plants in winter:

Trees and plants that are above the snow are the food for many herbivores. Seeds, bark and other living tissues are very wanted food, even conifer needles that contains resin are good enough. Many plants have chemical compounds to drive away unwanted visitors.

Those plant parts that are above snow are very cold and dry tolerant: same shoots that may die in summer when it’s about 5 - 10 degrees can tolerate coldness in the winter which can be -30 - -60 degrees. The root system of trees is well sheltered but they are usually very sensitive to cold if compared to those parts that are above the ground.

Plants are exposed to coldness and to dryness. Still pine and spruce keep their needles over winter, usually many years. Sakari Topelius says: ‘They are having their dormancy as well, but they are warriors, they are used to sleep with their full equipment.’

We remember very seldom how evergreen our nature is, conifers, most of the dwarf shrubs, mosses, lichens and even some grasses, there are greenness under the snow, too.. It’s no use to waste resources if they can be maintained over winter for the needs of spring.

But many above ground parts of grasses, some buds near ground may survive, die when winter comes. It’s safer to overwinter in the ground than above it. Except snow, detritus-, moss- and humus layers are good shelters, too. Many dwarf shrubs of forests have huge amounts of roots, runners, under ground. It’s very important safety storage against coldness, dryness, forest fires and so on. Annual plants have only seeds, and sometimes they aren’t mature enough before winter. That’s why we have so little annuals, extinction is very serious threat.

Many of our plants drop their seeds during winter or during next spring. For example most of our tree species, dwarf shrubs and many grasses that have dead sprouts above the snow. Along the surface of snow or with animals seeds may end up far a way from their ‘mother’ plant.

Trees can have huge amounts of snow in top of them. One middle-sized spruce may have few tons of snow. No wonder that branches and tops breaks off, especially high lands in Lapland and in Kainuu. Is the northern spruce with its short downward branches adapted to this snow amount? Still snow damages are common in spruces as well near timberline. See: picture 2, picture 3, picture 4, picture 5, picture 6, picture7 and picture 8!

Several natural plants groving in the north must - in spite of many problems caused by winter - undergo cold stress in wintertime. Those plants have a need to wintertime (= vernalization). To start the growth in the spring they need to meet with cold at least a couple of weeks. Same concern to the germinate of seeds of many plants. - The term vernalization is often used to speed up the growth of plants with cold-handling (or hormonal handling).

Winter active animals

- About birds you’ll find from the birds-parts of this programme.

February is the most critical month for small birds. Many small birds, for example bullfinch and tits move near people, it’s easier to find food and warmth. Some other birds travel in to far away countries to find food easier. For example the migrations of bohemian waxwing after rowanberries are well known or redpolls south trips after birch and alder seeds. Also woodpeckers, crossbills, pine grosbeaks, Siberian tits, dippers and great grey owls migrate after food. Small birds have to eat a lot during cold period of mid winter, the whole day light time, which is not long. The body temperature has to maintain even 60 -70 degrees higher than the outer temperature.