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The sructure and production of forests

In the picture with ripe lingonberries, there are also Scots pines (Pinus sylvestris)
broken by the snow ('tykky'-damages) on the timber line of Riisitunturi fjeld, Posio.

Little plant mass - small output (primary production)!

- Most of the phytomass of plants is in the humus layer.

- The life is mostly in the surface of soil where there is hard competition over resources and living space.

- The cool humus layer is very good basement in the summer and cover for energy and resource supplies in the winter. During summertime the thick humus layer also restricts the effects of, for example, forest fires.

- Vegetative reproduction is very common in the north. It is a better guarantee that life continues than sexual reproduction.

- Carbon is stored in old forests (for example in humus) and in the peat of mires. This has very important meaning in restricting the greenhouse effect.

Most amount of nutrients in the trees - especially nitrogen - are in needles.
There are very small amount of principal nutrients in the trunks.


Production of new phytomass or nettophotosynthesis (= quantity and speed of nettoproduction) depends on several factors, especially on the amount of green parts ( like on the amounts of leaves, leaf area and chlorophyll content in trunks). Conclusive environmental factors are among others season, temperature and its fluctuation, moisture in soil, oxygen situation and availability of nutrients.

The amount of carbohydrats reduce once buds will open in the spring, also before the leaves are completed. Decreasing of carbohydrats down to since those carbohdrats, that were in winterstocks are in the spring using for growth of shoots. More: Fluctuation of carbohydrats in the plants!

Carbohydrats are decreasing in the plants that produce berries or fruits in the time of ripening. When the plant growth in aboveground parts is terminating, the stocks of carbohydrats will often decrease, because the non-green parts (of stems and roots) and the stocks of carbohydrats (of stems and roots) are still growing. It has not find this kind of summertime degresing in the mosses. In all plant species decreasing of carbohydrats on the long wintertime is common: not photosynthesis but yes the respiration!

Forests, mires (and treeless fjeld) are typical nature of North. The amount of phytomass (= biomass of plants) is insignificant in the northern nature and the number of species is low (cf. phytomass of HMT!) This represents among others that the consumption pressure against every animal and plant species can perhaps generate some damages in total ecosystem (cf. biodiversity!).

The phytomass of Finnish forests is an average about 100-300 to/ha, only. In treeless mires it is about 10 to and in barren lakes even less. However the importance of undergrowth (dwarf shrubs, mosses, lichens) is frequently well developed and rather dense, because lighting and moisture are normally sufficient on the bottom of forest, too. The importance of undergrowth is remarkable to food economy of forests.

mantu kk

The different age classes of needles can easily see in the old pines,
because it is a gap between the needle-rings.
The male inflorescences was situated in those gaps.
Some individual of pines are capable to generate lot of
male flowers - more than some others. There are about four
needle-rings in the pine of this picture. This is rather
normal situation in the north..

Year after year - especially in the autumn and every winter - lots of phytomass will die. This is relevant, because it is not a good idea to keep up too much living tissues in the killing temperature and in the winter dryness. The coniferous trees reduce the amount of needles in the autumn extracting about 1/5 of the needles. The same quantity of needles have to rebuild in the next spring. Capability of the photosynthesis will reducing year after year, and so the old needles are almost incapacitated. However the recurrence of green phytomass of coniferous trees is quite exiguity compared with herbs, whose must rebuild in every spring almost all green parts. (More: preparation to winter!)

The undergrowth (dwarf shrubs, mosses, lichens) however, is often quite well developed and dense, because there is enough light and moisture available even on the forest floor. The role of the undergrowth for the nutrient balance of the whole forest is therefore significant. The life concentrates on the upper parts of the soil, where an intense competition for space and resources takes place.

The main part of the living tissue of most northern dwarf shrabs and even grasses is underground. If the humus layer is thick, even 2/3 of bilberry shoots may grow underground! A relatively small amount of green tissue is therefore capable of sustaining roots, non-photosynthetizing shoots and other living tissues of the plant.

The cool humus layer is also an excellent cellar: the energy stored there "gets depleted" slowly. The humus layer can function as secure storage as well: if frost, forest fire or herbivores destroy the above ground growth, life is still sustained beneath the earth (although the root tissue is fairly susceptible to cold). The new vegetative growth after such a catastrophe is usually very vigorous. See also: soil!

Many northern plants allocate resources especially for vegetative reproduction, even though there is also seed production. Large seed production requires quite an amount of resources, and the other vital functions such as growth or defence might suffer. For some plants sexual reproduction by seeds is up to 10 000 times more "expensive" than vegetative reproduction by runners or shoots.

Sexual reproduction, however, enables faster adaptation (gene exchange) than vegetative reproduction (i.e. cloning). In Lapland there are very few annual plants. In the north being annual is a great risk: if the seed production fails, the plant will inevitably perish. The beginning of the growth is not always successful, especially if the raw humus layer is thick and dry. In difficult conditions cloning is at least a more secure strategy of life and reproduction. One could think that flora originating mainly from the forest on our bare fjeld tops is a relict of 5000 years, when the tops were covered with forest, and has been able to survive with the help of snow cover and vegetative reproduction.

The annual production rates in northern ecosystems are quite small (see phytomasses of HMT!) and recovery from damages is slow compared to more southern regions. This is despite the fact that abundant light and cool summer is a profitable combination when considering energy consumption. The net production (i.e. the visible new growth) of boreal coniferous forests is, of course, many times larger than the net production of treeless tundra. Given in numbers the annual phytomass production of boreal coniferous forests is 5-10 tons per hectare, which at the most is 5% of the whole phytomass of these forests.

Therefore, the annual interest is not very high compared with the capital. This is mainly because of the weak growth potential of the trees. The undergrowth of the forest, gives a substantially better interest to its capital, not to mention the aquatic environments, where the whole phytomass might renew annually. The efficiency of the exploitation of available solar radiation is relatively good even in the northern forest (i.e. approximately 0,75%, which is only slightly lower compared with the deciduous forests in central Europe).

Hylocomium-Myrtillus-forest type (i this case pine growing) in the area of Peräpohjola boreal zone.
The bristle undergrowth (dwarfshrubs, mosses) is generating well but the treelayer (old spruces) badly.

The respiration of the northern trees requires relatively little energy, but for the plants wintering under snow the situation is quite the opposite. For example, in good summer conditions a single bilberry plant can bind 10-15 milligrams of CO2 per gram of green dry weight in an hour, but it consumes four to eight times less, so the growth is still fairly good. Instead, lichens as well as mosses grow slowly mainly because of the dryness of midsummer. On the other hand, their growing period is long because they are capable of photosynthesis even in zero temperatures.

The northern forests and marshes in particular, have an important role when considering the quality of the Earth's atmosphere: carbon is stored within the peat of the marshes and forests. From peat it ends up in the mineral soil and forms a nearly permanent reserve. Thus, these ecosystems, and not the tropical rainforests as is often claimed, are the true "air fresheners" whilst considering the threat of greenhouse gases. Of course, a young vigorously growing forest also binds carbon effectively.

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