One fifth of the growing timber stock in Finland is in stout trees. This equals 415 million cubic metres of timber. Stout trees mean trees with a trunk diameter of 30 centimetres or more at the height of 1.3 metres.

The amount of all-sized trees has increased in Finnish forests. However, the share of stout trees has increased. In the 1960’s 15 percent of timber was in stout trees, currently the share is 19 percent. The amount of stout trees has increased especially in southern Finland.

Since the 1950’s, the volume of stout spruces and broadleaved trees has quadrupled. Now, a quarter of spruce volumes is in stout trees. The one exception is pine; the share of stout trees of its volume has decreased a bit.

Foto: Krišjānis Grantiņš

Also, there are more broadleaved trees in Finnish forests than there has been in decades. Both the volume of broadleaved trees and their share of growing stock volume have increased.

Best trees are left growing
Researcher Kari. T. Korhonen from the Finnish Forest Research Institute says that there are several factors behind the development.

”In the 1950’s, forests looked a lot different than nowadays. In those days a big part of the forests were so called selection forests: the larger trees had been continuously removed from them for decades. A typical forest was 40-80 years old,” Korhonen says.

The current forest management method, which has been prevalent for a long time, has not allowed such selection. Forests have been grown even-aged and the aim of thinning has been to remove the smallest and lowest-quality trees. Forests are regenerated when they reach the criteria set for it.

The current Forest Act stipulates that, depending on the growing conditions, the trees must have an average diameter of 25-28 centimetres, before they can be felled. This criterion does not, however, explain the increase of trees over 30 centimetres thick.

Forest owners’ profit goals fatten trees, too
Korhonen says that another factor behind the increasing stoutness of trees is that some forest owners aim to get the best possible profit from their forests. Letting the trees grow stouter is profitable as the share of the valuable sawn timber log part of the trunk increases considerably.

About 70 percent of the forest owners’ timber sales income comes from selling sawn logs, the rest from smaller-diameter pulp logs. On the other hand, some forest owners have their forest felled as soon as it is mature.

Another reason for the trees getting stouter is that less timber is felled than what could be felled. Finnish forests grow around 103 million cubic metres ever year. The maximimum sustainable annual felling would be 70 million cubic metres. In 2010, 55 million cubic metres were felled.

”The background reason could be that people can afford to wait for a time which is best for them to fell to forest. Thus they let the forest grow. Also, timber sales revenue is not the only benefit expected from forests,” Korhonen thinks.

A major share of pine forests are young
Korhonen, project leader for the National Forest inventory, says that the young age of pine forests and the slimness of the pine trees are clearly seen in the inventory.

A major part of the 40-year-old or younger forests are pine forest because for a long time, pine was used in regeneration regardless of whether it suited the soil or not.

Some of these pine forests are yet to be thinned and thus the trees have remained slim.
Forest owners carry out less and less forest work by themselves. This has contributed to the increase in broadleaves, too. “People do not make as much firewood as they used to do still in the 1950’s. And birch was the choice tree for firewood,” Korhonen says.

Forest management guidelines and forest certification have for the past 15 years encouraged leaving more broadleaved trees in forests. Korhonen says that their effect can be observed in the increasing amounts of retention trees and decayed wood in forests.

By Krista Kimmo
forest.fi