The Finnish Ministry of Agriculture and Forestry started a work to revise the Forest Act this week. The purpose of the work is to increase the forest owner’s options in forestry activities.

In principle, alternative methods for periodic cover silviculture (see: Glossary) have not been forbidden in Finland. There are only two obligations set for the forest owner in the Forest Act: after felling for regeneration a new forest stand has to be established in due time. As for the thinnigs, too much timber may not be cut.

As an example, in continuous cover silviculture there are no fellings for regeneration, as well as there is no need to establish a new forest stand, since, according to the theory, a new forest stand will appear naturally. In reality, however, such heavy loggings have been made under the name of continuous cover silviculture that the authorities have interpreted them as final felling.

Thus, disputes have occurred on whether the forest owner should or should not establish a new forest stand after this kind of disputed felling. The Forest Act does not give any clear guidelines on how to proceed.

There are several alternative methods
Almost all logging methods where the amount of cut timber per logging is smaller that in felling for regeneration have been called continuous cover – or uneven-aged – loggings. For the result of the forestry it is, however, significant, which is the alternative method: selective thinning of largest trees or according to some other principle, or logging of small gaps.

For example, in logging of small gaps the target is to make distinguishable clearcut areas with a diameter of 30–40 metres, which after felling should start to grow new plants naturally.

The profitability of different methods should not be evaluated only according to growth or the quality of the timber. Especially in the long run it is essential that the forest will survive – which means that new trees must occur after felling.

Biodiversity can also not be evaluated according to just one parameter. All forestry methods are beneficial for some species and harmful for some others. “Scoring” the ecology of a single forestry method means decisions on which species need more and which less safeguarding.

There is no more decayed wood in a continuous cover forest that in any other commercial forest, if valuable, large trees are not left there on purpose in connection with fellings. The trees are not larger and there are not more forest fires or burned wood.

Continuous cover silviculture does not favour species of open environments. These species do exist in periodic cover silviculture forests. Also species of closed environments do live in these forests, especially at the end of rotation period.

Some research is made, but not enough
The Finnish Forest Research Institute carried out a research project called Biodiversity in commercial forests in 1995–2005. The growth, regeneration and biodiversity of periodic cover silviculture – with and without retention trees – as well as small gaps and selective loggings were studied in the research.

The research was carried out in spruce-dominated forests. In the cases of selective and small gaps loggings the regeneration was meant to take place naturally, with the exception of applying light harrowing on certain small gaps logging sites. In clearcutting areas the stands were harrowed as well.

“There were no big differences in the number of plants growing on the sites. Harrowing was not of great significance either,” says senior research scientist, Mr. Sauli Valkonen from the Finnish Forest Research Institute.

However, after ten years of establishing the new forest stand, the plants growing on clearcutting stands were much larger than on the other stands. “Since then the planting methods of spruce have developed crucially. This makes the difference of today clearly larger,” says Valkonen.

The difference means that the plants growing on the stands of small gaps loggings were growing ten years “behind” the ones of clearcutting stands. This lengthens the period needed for a plant to grow to stout timber by even 15 percent. The income of the forest owner can be assumed to decrease as well.

Uneven-aged structure is not easy to maintain
Logging of small gaps does not necessarily maintain the forest cover easily. If the new forest will start to grow slowly it is possible that the stand nearby must be logged before the first one has grown satisfactorily – which means that one maybe should discuss of continuous logging instead of continuous cover silviculture.

On the other hand, if the logging is postponed in order to keep the forest cover continuous, the growth and profitability will decrease.

However, stands logged according to the small gaps method are easier to regenerate and grow than the forest logged by selective loggings. Valkonen questions, if it is in general possible to sustainably maintain the uneven-aged structure of forest cut by selective loggings.

“In some research projects made in Norway and Sweden the target was to maintain the uneven-aged structure for 30–70 years. Half of the stands failed,” says Valkonen.

The reason is in the very poor ability of a forest to regenerate naturally after selective logging. When no trees of new generations occur, the uneven-aged structure inevitably starts to vanish from the younger end. Species favouring light, such as pine and broad-leaves, are in danger of disappearing totally.

On the other hand, the yield of the forest may stay on high level for tens of years, which may mislead the evaluation of the method. “It may be that incorrect selective loggings one after another lead, after a relatively good period of yield, to a situation where the forest is full of deteriorated trees. Then clearcutting is the only possible forestry method to be taken,” says Valkonen.

Criteria can be formulated for residual timber
Valkonen reminds of one more difference between the forestry methods, the so-called loss in value growth. When a tree reaches sufficient age, its rate of growth decreases and damages start to occur. If felling of these ageing trees is postponed, the growth rate of the forest as a whole decreases as well.

In addition to this, there are several factors affecting on the profitability in practice that the research has not been able to take into consideration so far.

According to Norwegian and Swedish research the profitability of alternative forestry methods, if carried out successfully, is 10–20 percent lower than that of the traditional one. However, calculations are theoretical and not final in any way.

Under which kind of conditions one could then say that forest has regenerated also when continuous cover silviculture is applied? According to Valkonen, the law should be written in such a way that it can be applied to all forestry methods, and it cannot be complex in any way, too.

“We could define how much timber, in square or cubic meters, should be left as proper, viable trees per hectare in the forest after the felling. If the necessary level is not reached, one should regenerate the forest,” says Valkonen.

This condition would be simple, unambiguous and easy to monitor. In addition to this, it can be applied in clearcutting forestry as well.

By Hannes Mäntyranta