It is estimated that the growth of the Finnish forests may as much as double due to the climate change. These estimations are based on research carried out in the 1920s by Professor, Mr. Olli Heikinheimo.
Heikinheimo found that the growth rate of seedlings originating from northern Finland was twice as much in Lapland compared to when they were planted in the south, where the average temperature was four degrees higher.
According to Professor, Mr. Kari Mielikäinen from the Finnish Forest Research Institute, these rates will hardly be realised in actual life. “During winter an increase in temperature does not increase growth, rather the opposite. The trees do not grow in winter, but increased warmth might increase the respiration of trees, which would delay the start of the growth period,” says Mielikäinen.
The increase of extreme climatic conditions would also create problems. More frequent droughts would lead to growth losses especially in the spruce forests of southern Finland.
There is no research-based information about stronger winds, but even if wind strengths do not increase, the damage caused by winds will do so. “In the autumn, when the ground is moist and unfrozen, the trees are easily toppled by winds, especially if stands are originally dense and are then thinned intensively,” says Mielikäinen.
Higher temperatures increase both growth and risks
The climate change increases the growth of all plants for two reasons: the amount of carbon dioxide in the atmosphere and the air temperatures both go up. Other research scientists in the Nordic countries have studied these phenomena for their effects on pines in Mekrijärvi near Joensuu, Eastern Finland, on silver birch in Suonenjoki, Central Finland, and on spruce in Flakaliden, Northern Sweden. The researchers have attempted to capture the conditions that, according to forecasts, will prevail in a hundred years.
The results show that the growth of all tree species increased. The largest increase was with pine, the diameter of which grew by 60 per cent more than in the current climate. The stem volume of silver birch increased by 40 per cent, although there was considerable variation. The increase in spruce growth was smaller.
It is estimated that the temperature increase would result in an additional growth of 20–30 per cent in Southern Finland, and 50 per cent in the north, if other factors remained unchanged. The growth increase seems to be largest with broadleaves.
In Mekrijärvi it was observed that an increase in temperature alone brings about less increase in growth than a simultaneous increase of temperature and carbon dioxide.
However, more warmth also entails risks, which, if realised, would lead to growth losses. Such risks include fungous diseases, as well as damage and diseases caused by insect pests.
Currently the cold Finnish winters control the prevalence of insect pests, but this might change in the future. And if the summers become warmer, pests might be able to produce several new generations annually. Trees might also suffer other kinds of damage, such as heavy snow burdens on the branches due to additional snowfalls during winter.
The climate is changing in other ways as well. For example, the amount of ozone in the lower atmosphere may increase due to noxious emissions from traffic. Ozone decreases plant growth, and its effects are cumulative, so that they might only be seen after several years.
The ozone-related growth loss of forest trees has been estimated to be as high as ten per cent. Thus, it may neutralize the increase caused by the higher level of carbon dioxide.
Warmth does not lead to growth without nutrients
The well-being of trees depends not only on the climate, but also on the soil. If the soil is poor in nutrients and none are added, growth will remain smaller, no matter how the climate changes.
There will be no major changes to the occurrence of tree species in Finland if the climate changes as forecast; it is not certain that southern tree species could thrive in Finland’s nutrient-poor, acidulous and often moist soil – in marshy areas, for example. However, it is possible that new broadleaved tree species now growing in the warmer Central Europe, such as poplar, will begin to appear in Southern Finland.
Trees are also adapted to certain annual variation in light conditions, for example. The trees begin their winter rest according to their genetic inheritance, no matter how warm the weather is. That is also when the growth ends, regardless of temperature.
According to Mielikäinen, the climate change forecast for the next 50–100 years has no significant effect on forestry methods, at least in the case of northern Finland. However, it is possible that the most productive forest zones will move slightly northwards in the country.
“Although a warmer climate favours broadleaves, the forests will not become dominated by birch if they are regenerated with coniferous trees. The stout spruce forests of Central Europe prove that conifers also thrive in warmer conditions,” says Mielikäinen.
However, higher winter temperatures may make timber harvesting more difficult. In Finland, a lot of harvesting will in the near future be carried out on peat lands drained some decades ago. On such soils, harvesting must be done when the temperature is below zero and the ground is frozen.
If the temperatures rise above zero, the ground will thaw. So far no one knows how to harvest timber in these conditions, although appropriate harvesting technology is being worked on.
According to Mielikäinen, it is forecast that, due to the running out of fossil fuels, the atmospheric temperature may begin to decrease before 2100. If this happens, the climate change will leave its traces in the annual rings of one tree generation only.
In this case the trace would be smaller than that of the warm, several hundred years’ climatic season which ended in 1400 C.E.
“To make this happen, we must go on with research-based efforts to control the climate change,” says Mielikäinen. By Hannes Mäntyranta