On Tapio and Hannele Airola’s farm in Kärkölä, southern Finland, grows a 24-year-old, two-hectare birch stand. The stand in question is a good example of a Finnish birch forest that has been taken care of properly and at the right time.
Birch thrives on sunlight, which means the stand must be sufficiently thinned to ensure that the remaining birch trees receive enough light and nutrients. The Airola’s birch stand has clearly received enough of both, as their trees are currently some 18 centimetres in diameter at chest height and 20 metres tall. The trees will soon stop gaining height, but their girth will increase for some time.
The good present state of the birch forest can naturally be attributed to the efforts of the Airolas themselves. If the thinnings had been delayed, the area would now be dominated by slender birch trees.
The Airolas planted their birch stand in 1991 – the same year their son was born.
- The idea was that he would be able to cut down the birch forest to celebrate his 50th birthday, laughs Tapio.
Koskitukki’s purchasing supervisor Heikki Nikkinen is quick to interject that he might be able to start the felling work as early as his 40th birthday.
- At this rate of growth, after 40 years the birches will be 40 centimetres in diameter, which will be the perfect time for a regeneration felling.
The forest that grew on the land before this birch stand was felled in 1989, when Hannele worked as Koskitukki’s first female lumberjack in her own stand and harvested the forest in question. The harvester used at the time was not able to cut down the largest trees in the stand, so, following some instruction, Hannele cut them down with a chainsaw.
The first thinning was carried out on the forest in 2005 by Hannele, who also transported the felled logs by horse. The logs were transported by tractor from the side of the trunk road to a larger roadside storage site to await lorry transportation to the mill.
Now, 26 years after the regeneration felling of the previous generation of trees, Hannele and Tapio are once again thinning their birch forest. After this felling, there will be roughly 350–400 birch trunks per hectare left in the stand.
In Finland, 1,600 birch saplings are usually planted per hectare of land; the figure is slightly less than the number of coniferous saplings planted. The first thinning is carried out when the birch trees have reached a height of 12–14 metres, and the number of birch trunks drops to some 700–800.
It is important that the tree’s living crown accounts for roughly half of its length to ensure that growth is strong and the tree gains girth. In an ideal location, birch can grow a metre in height and a centimetre in diameter in one year. Birch trees are ready to be harvested once they have reached a diameter of 35–40 centimetres, i.e. between the ages of 40 and 60, depending on the forest.