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Spring is in this screen!




The timing of bird migration

See also: Ecology!

Spring is coming…

If black grouse starts to ‘sing’ in the beginning of February the spring is going to be even and good (old weather forecast).
During warm February nights you can already hear owl’s courtship hooting.
Swallow starts its migration from South Africa to Finland in the end of February.

At times it is almost summer but then again, cold spell in spring

Meteorological spring starts when the average temperature of a day rises permanently above zero. In Kainuu, this takes place in the middle of April, in Lapland not until at the end of April or at the beginning of May. As long as there are snow and ice, the average temperature does not easily rise to summer temperatures but stays around 0-10 Celsius degrees. Nevertheless, the snow may melt quickly in the rainy days of May – snowdrifts will flop. First the snow will disappear from open areas, and only a couple of weeks later from forests. Naturally, the snow will melt from the forests of Lapland much later than from the province of Oulu.

Sea and big lakes will be freed from ice late in spring: it is possible that one might see ice floats in the northern part of the Gulf of Bothnia as late as at the end of June. The northern part of the Gulf of Bothnia cools the spring air: sometimes there is not a trace of green in the birches of Tornio, even though the trees in Rovaniemi are already in the bud! On the other hand, the sea warms in autumn – the arrival of winter is delayed. Night frosts last quite long in spring but in June they become rarer. Frost melts from Lapland earliest in June, sometimes not until the late summer. In some years, the frost does not melt at all deeper in the ground. If this kind of situation continued a few years running, a new ice age would be very near!

In the fjeld areas, where the wind has beaten the ground, there has been a very little snow all through the winter, and the places where the snow has melted grow fast. But so-called snow banks where melting has delayed, and where winds of the winter have collected high snowdrifts, may have “old” snow even in August-September. At the same time, new snow is already snowing. When the fjeld snow of Lapland finally melts, it may cause another spring flood (a summer flood, to put it more exactly) in the lower course of big rivers.

First sunbeams into the forest...

The actual melting of snow is a fairly short period even in Lapland, mainly in May (at the beginning of June in fjeld areas, at the end of April in the province of Oulu). Because of that the rivers in the north may overflow wildly. In big rivers, water rises several metres in spring, and causes wide floods. This happens especially when the ice breaks up in thick floats and packs in areas of rapids preventing the flowing of water. In the water system of Northern Finland, those kinds of big lakes which would gather melt waters to balance the peaks of flood are scarce. However, there are still wide string fens that work as flood reservoirs. But in the province of Oulu, many fens have been ditched, and the floods have become more common. Several of the big rivers of the north are regulated but even the regulating reservoirs may fill up to the brim - or even over it - in spring.

Melt waters and spring floods affect the living nature in several ways. In aapa (string) mires, floodwater “builds” the miniature topography of the fen; e.g., hummock ridges and flarks (which are usually vertical with respect to the direction of the flow) are the makings of melt waters. Along rivers – in places where water flows quickly – ice cakes restrict the birth and growth of e.g., shore forests by damaging the plant cover and soil cover. Several mosses, dwarf shrubs and e.g., pine do not like silt or floodwater cover. In places, where the flow is slower e.g., willows and broad-leaved trees manage to create grove-like shore forests and bushes; every year floodwater brings natural silt fertilisation to riverbanks. Particularly in fertile areas (e.g., in Northern Kuusamo and the triangle of Lapland), the silt markedly improves the nutrition conditions of the soil. This was noticed already by the river side settler who cleared forests into fertile flood meadows. For example, in the flowering time of globeflower (Trollius europaeus), many of the natural shore meadows (if you can find them nowadays!) of the northern rivers are very beautiful. By following flood meadows and gravelly soil of river banks, many plants have wandered while gaining new areas. For example, from the north, some species have wandered towards the south by following the gravelly river banks. Large pink (Dianthus superbus) is one of the plants that have arrived in Finland from east.

When the snow cover disappears…

The disappearing of snow cover in spring is an enormous and quick change of habitat for plants and insects that have wintered under the snow. During the long winter (as long as even 6-7 months), it has been dim under the snow day and night, and completely dark in mid-winter. The amount of light is nearly nonexistent already a half a metre under the snow cover even in spring. Then, suddenly these organisms are met with a bright summer – it is bright even at night!

Furthermore, the temperature has kept its balance under the snow: only seldom has it fallen below zero. The “climate” under the snow is marine also in the sense that the air is humid: relative humidity around 100% for long periods of time. Moreover, carbon dioxide caused by respiration accumulates under the snow (all the micro-organisms and plants respire), sometimes very much in spring. In snow, hollows form around the plant, e.g., around twigs, when the dark stems melt snow as they are tying heat radiation; tiny greenhouses will develop. These conditions would be quite good considering the beginning of growth but then suddenly, as the snow cover disappears, temperature starts to fluctuate from night frosts to even high temperatures in the afternoon.

Sun may warm the plants during the day: pine needles are as much as 10 Celsius degrees warmer than air in the sun – and the next night, it may be over 10 Celsius degrees below zero… In addition, the air humidity varies greatly at that time. The risk is great for many plants considering the first stages of growth. It is no use to grow too much or too early under the snow! Nevertheless, the buds of many plants (e.g., blueberry) swell somewhat under the snow already. But, for example, pine wakes up slowly. The first warm days are not enough to activate the assimilation.

In Lapland, there are often those kinds of springs, when plants (and other awaking poikilothermics) have to face the warmth of summer directly after the winter under the snow: thermic summer has already started before the snow cover has completely disappeared. This kind of situation is almost always usual in the areas where the melting of snow banks has delayed. In that case, the growing season remains quite short.

Melt waters threaten the spring of several animals: the place of winter dormancy is in danger of being covered with water. In Lapland, bear and lemming as well as many small invertebrates of the soil are often met with this situation. And, also people have suffered from spring floods in the past when they have not been able to go out and about during the thaw season.

Are the energy stores enough?

Most of the poikilothermic plants and animals (e.g., insects) that winter under the snow spend their winter in torpor (dormancy). During the winter, the consumption of energy is low; the animals live frugally, mainly supported by the energy that they have gathered the previous summer (extra nutrition). Nevertheless, long winter – particularly, in the “warmth” under the snow - may consume most of the energy even in dormancy until animals and plants can generate new energy. In spring, the animals and plants must live for a while with the energy they already have (e.g., meny grass plants have to build a totally new assimilation system). Some of the plants – e.g., moss, lichen, coniferous trees and even several of the twigs - have chlorophyll that has preserved over the winter, they are evergreen. Some of those who shed their leaves for winter have chlorophyll in their stem cell tissue, e.g., blueberry or birch. With it, they assimilate even before the new leaves have come out.

Several plants have energy stores especially in their subterranean parts, rhizomes etc. And there are often a lot of rhizomes, e.g., with blueberry of the north, the subterranean phytomass consists of 2/3 of the whole mass! Only the part that reaches above the ground assimilates. Thus, subterranean parts live parasitic life but an important life, though. Furthermore, new growth begins in the subterranean parts in spring – if not in winter already.

The winter fat stores of mammals are discussed in winter text.

The growing season begins…

Officially, the growing season begins when the average temperature of a day exceeds permanently +5 Celsius degrees. In Northern Finland, this takes place around the middle of May and the beginning of June. In April, the first big areas where snow has melted appear under the trees and on sunny slopes. But even before the whole snow cover has disappeared, the life of several plants will be in full speed. The fact that summer in the north is short accelerates awakening. However, the sun is up also in the night so at its best, assimilation is possible all through the day and night. The best net output can be gained in bright but cool period of time, i.e. during the night of the north; at that time, respiration is minimal and assimilation efficient.

Grey alder (Alnus incana) and many willows (Salix) as well as some fjeld plants (e.g. purple saxifrage, Saxifraga oppositifolia) blossom even when there is snow or at the latest when the ice breaks up. Purple saxifrage flowers a couple of days after the snow has melted! Moreover, hare’s-tail cotton grass (Eriophoprum vaginatum) starts flowering early in spring; peat is still frozen solid when the sprouts of hare’s-tail cotton grass rise from peat, and black inflorescences with yellow stamens appear. Also crowberry (Empetrum hermaphroditum) opens its small flowers early. There are also many other similar examples in the north. One of the reasons for the quick early development is exactly the long period of light and another reason is that flower buds have been developed almost to the finished stage the previous autumn.

However, the north does not experience spring aspect the same way as the south with flowering anemones and other spring flowers in the forests. One of the reasons for this is that the lightness in the northern forests is almost always the same due to the tree stand (the coniferous trees!), whereas the southern forests turn into quite shady places as the broad-leaved trees are finished with their foliage. Flowering requires light, as do many of the pollinators. Perhaps, the most important flowering plant of the early spring for insects is willow. There are great amounts of willows in the north, and many species, too!

Forest research institute has started (1998) an extensive collecting of phenological material of some of the forest plants. The material collected up to now beautifully shows the regional and annual differences between various species. For example, the coming into leaf (budding) of forest trees takes place at the end of May in Southern Lapland but in the most northern parts Lapland this does not happen until the early June. On the other hand, the flowering of blueberry takes place a week or two earlier in the southern parts of Lapland than in Southern Lapland. The accumulation of the temperature sum of the early summer, among other things, significantly affects these kinds of differences.

- More phenological material of METLA!

- Moore other phenological material!

The spring frolic of animals…

The liveliness of winter active animals increases visibly in spring, even when there is still snow. One can see numerous of tracks on the snow. The animals are merely preparing a new life… However, bear and wolverine have given birth to their offspring already in the middle of severe winter, and lemming has also had young ones under the snow in winter, and perhaps even several times. As the snow melts, also reindeer calves. Furthermore, crossbill and Siberian jay have their nests ready, and perhaps even their eggs.

The time of new live goes on all through the spring and early summer. During the days, squirrels chase one another enthusiastically and make all sorts of sounds (but not beautiful ones!). During the nights, the same wild hustle and bustle goes on, e.g., with hares (first youngs in this year will be procreated). One can hear lots of voices also at nights: owls hoot, a fox might shriek, and in the early morning one can hear the chuckle of black grouse from somewhere far away. The cry of a raven that has been heard all through the winter is accompanied by the shrieks of the first migratory bird of the north, the crow (Corvus corone).

Soon after this, the migratory birds start arriving in masses. Approximately 20 million individuals winter in Finland but in summer, there are as many as 100 million birds! Some come from far away; the journey of those who come from Africa lasts as long as 2-3 months since they have to rest and eat now and then. In the north, there is room for nesting, great amounts of insects for food, and a long and bright day for the searching of food – it is worth coming here! You can find the schedules of migratory birds elsewhere in this programme. Soon, the chaffinch will begin its energetic and loud singing. And after that the willow warbler will start with its melancholy tones. Sometime in June, one can hear the call of a cuckoo, spring ends… There are not very many good singers in Lapland but bluethroat (Luscinia svecica) is worth mentioning. It has sometimes been named the nightingale of Lapland.

In addition, the first insects appear in the north during the time of the crusty snow in the spring. In a warm spring day, springtails (Collembola) venture out even above the snow in swarms. They have wintered in the ground and climb all the way above the snow to find food. There can be thousands of springtails in each square metre; they are important, for example, in forest nature as decomposers of forest litter. Early in spring, on the shores of rapids, one can find stone flies (Plecoptera) that have just hatched out from water. Early in spring when the weather has warmed and it is calm, chironomids come to have their spring frolic, sometimes even in very big swarms (only males!). There may also be some snow insects or spiders crawling on the snow in spring. The pictures of some actual snow insects can be found in winter text!

Some butterflies winter in Finland as adults (e.g. small tortoiseshell, mourning cloak and brimstone). Therefore, they appear early in the sun to warm themselves – and to lay eggs. Fertilisation has taken place the previous summer already. First butterflies that are common also in the north and that do not winter as adults, are e.g., small green hairstreak (Callophrus rubi) that winter as pupae, and some blues. Moreover, some small butterflies are seen flying even when there is snow on the ground. Nevertheless, there is not much food at that time. Fortunately, willow – including goat willow – is already blossoming!

Spring is at end now!

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