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The diverse climate

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3. The diverse climate

The greatest risk of northern nature: climate!

Low temperature (= small thermal sum), changing weathers and relatively short summer restrict the function and production of biomass of northern species, populations and ecosystems.

Well-known geobotanist Ilmari Hustich used term ‘climatic hazard’ when he described the problems of Lapland’s nature.

From time to time everything is fine and then suddenly comes a catastrophe! The amount of resources and their distribution for different phases of life of organisms are very important in this risk situation.

Also the thickness of snow cover during winter has a great impact for organisms that overwinter here.

When speacking about climate, it usually means a macroclimate, which is measured in meteorological cabins situated 2 meters above the soil surface. The life forms are however leaving mainly in the microclimate, which is situated close to the organism. E.g. on the area where trees are felled, is very different climate compared with the spruce forest neighbourhood of logging area: there is more light, warmer in the daytime and often colder at night on the logging area, although the both places belong to the cool, boreal macroclimate.

Above: Kilpisjärvi is situated close to the northern forest line, Jyväskylä in Middle-Finland
and Vantaa in South-Finland.
The global mean temperature of July in the forest line is about +10°C. More: Snowforest climate!


Above: The growth of all plants - also tho growth of mountain birch (Betula pubescens ssp. tortuosa) - depends much on
the temperature of growing season. If a mountain birch is growing on the northern tree line, the significance of temperature
to growth and to all other vital functions is extra important. The temperature in the valleys on summer time
is high and so the growth is better. More: mountainbirch zone!

The effective temperature sum, which clearly correlates with several vital functions, accumulates relatively slowly in some summers, but then there are also summers when the mean temperature is above average. For example phenological phenomena (e.g. initiation of growth, florescense and seed maturation) indicate the differences between years, but they also indicate the flexibility of many plants. The florescence of a species can be delayed by many weeks on a cold summer compared with a warm one, or the growth in general may be poor. For example, the leaf emergence of the mountain birch in Kilpisjärvi varies from the end of May to the end of June.

This kind of variation puts a severe test to the physiological flexibility, and not only affects the genetic structure of the organisms and populations, but also the entire ecosystem and its structure (e.g. succession, see production of HMT).

The temperature fluctuation of the growing season is greater in the north than in the south. The fluctuation is especially notable in late spring and late summer. The big annual differences in the temperature at the beginning of the growth period are a problem for northern nature: incorrect timing during growth or reproduction could be devastating.

It seems that the growth and reproduction depend on the summer temperature, especially in the northern borders of plant distibutions. E.g. July teperatures of 20th century have been several times at high level in Lapland, too (see picture above!). The diameter growth and seed production have a rather good positive correlation to the warm months - but not always!

It is well-known that at the beginning of last century (especially 1920 - 1940) a warm period exists in Lapland, too. In that time the diameter growth and seed production of pine was good until to the northern border of pine forests. E.g. on the strength of these observations there begun large clear-cuttings just after second world war (especiallu in 1960th also in Lapland. But after some years the cold summers - and problems of reforestration - came back!

Now we are waiting so-called greenhouse-effect, which will rise the mean yearly temperatures Finland possible about 3 °C - and the rainfall will increase. All these changes will have large effects to the nature - especially in the north (in the areas of fjelds). See (greenhouse-effect!) and (C-balance!). In view of satellite pictures (NASA, 2001) the vegetationcover on the northern hemisphere is transforming thicker/greener during last 20 years (see the map, below!).

The threat of climatic hazards is also notable in winter. Although the winters in Lapland are usually long and very snowy, they are not exceedingly cold. Because of this, there are two ecological niches which greatly differ from each other: these are the environments above and below the snow.

It is 'warm', moist and dark under the snow cover. Such a greenhouse-climate under the snow may sometimes be disastrous: diseases (e.g. some moulds) may spread and oxygen may decrease because micro-organisms and plants respire a lot in 'warm' conditions under the snow. Therefore, the amount of carbon dioxide will increase and the amount of oxygen will decrease.

Days with snow cover: the indicated numbers are mean values 1961 - 1990.

All organisms above the snow cover (e.g. trees and bushes, insects that are in dormancy, and winter active animals) have to undergo severe winter: short daytime, coldness, dryness and hunger. Since the daytime is very short in the midwinter (see annual light period!), winter active animals (such as birds) do not have a very long daytime period to gather nutrients.

Our nature is quite well-adapted to a normal snowy winter. But if the ground remains without snow cover it might become frozen solid. If this happens, the root systems of trees, dwarf shrubs and micro and macro faunas in the soil can be severely damaged. In this situation, in Scots pine for example, only the new needles survive, the older ones die off after transferring the vital substances into the new parts. When the number of needles decrease, the reproduction and growth capacity become weaker. A cold winter with little snow can sometimes lead to a large loss of undergrowth, and that in turn dramatically alters the nutrient balance, relations between species and symbiotic relations throughout the forest.

It is "warm", moist and dark under the snow cover. Such "greenhouse-climate" under the snow may sometimes be disastrous: diseases (some moulds for instance) can spread and oxycen can decrease. The micro-organims and plants respire plenty of in "warm" situation under the snow, so that the amount of carbondioxide will increase and the amount of oxygen will decrease.

All organisms above the snow cover (for instance trees and bushes, those insects, which are in dormancy and all winter active animals) undergo severe winter: short daytime, coldness, dryness and hunger. Since the daytime in the midwinter is very short (see annual light period!), winter active animals (like birds) have very short daytime period to cather nutrients.

The special features of Lapland fjelds are a strong hoarfrost formation during winter and big temperature differences between the peaks and ravines, especially at calm, sub-zero-temperature times (temperature inversion). Sometimes significant damage can be caused to trees because of frost formation and snow load on branches ("tykky"- damages). The formation of frost and snow clumps is significant starting from 200-300 metres. Big differences in local microclimates occur between the upper and lower areas of the fells which means that there are different environmental conditions for different populations of the same species.

Getting prepared to endure the stresses of a long winter requires a lot of "work" and resources from organisms and begins during the summer. Sufficient nutrient reserves are particularly important (taking into consideration, new growth and reproduction in spring), as well as cold and desiccation tolerances. Many northern native plants tolerate desiccation fairly well (they are xeromorphic), but new tissues are especially susceptible to both cold and desiccation if the acclimation to winter fails. While a newly formed needle of a conifer can tolerate only a few degrees below zero in summer, the next winter the same cell tissue can tolerate temperatures down to -50°C and a dry period of 6 months.

Many northern plant species are evergreen and that makes growing easier to start in the spring: chlorophyll ready for assimilation is not only in buds and in leaves but also in branch- and trunk tissues.

Annual precipitation in Finland is quite poor (if compared the west coast of Norvay).
Precipitation is very low in the norternmost part of Finland (less than 500 mm/year).
The west coast and the sea areas of Finland are poor in precipitation especially in spring,
when the wind is coming from the sea.
- The precipitation numbers of Finland, Sweden and Norvay in this map are mean values of 1961 - 1990.

Generally speaking in maritime areas precipitation is bigger than evaporation and in continental areas the situation is vice versa (= large evaporation). All depend also on temperature, too: in the warm climate evaporation aspires to be bigger than precipitation (if water is enough).