This method is common in Finland, Norway and Sweden. It was introduced in Sweden by Tham (1988) with some modifications by Johansson and Lundh (1991). Currently, the same technique is used for birch and Norway spruce in Finland, Norway and Sweden. The principal aim is to create an initial mixed stand with an optimal density of birch.

The method involves two or three steps:

1. When the spruces are 1.5-2 m tall, the density of birch is reduced by cleaning to 800­1000 stems ha-1.

2. The "birch shelter" is cut when the birches are 30-35 years old with a diameter at breast height (dbh) of 15-20 cm.

3. An alternative is to cut all 30-35-year-old birches except 50-100 stems ha-1. The remaining stems should be evenly spread through the stand. These birches will produce high-quality timber during the following 20 years.

1.1.1 The “Kronoberg” method

This method was first introduced in southern Sweden (Anon., 1985). The aims are to avoid frost damage to Norway spruce plants and to control the number of sprouts that are able to establish after the removal of birch in each step.

The method involves three steps:

1. When the birches are 3-4 m tall the stand is cleaned. A total of 3000-4000 birch stems ha — 1 should be retained. The Norway spruce is not cleaned.

2. When the birches are 6-9 m tall the stand is cleaned again. A total of 1000-1500 birch stems ha-1 should be retained; the dbh of the birches should be about 5 cm.

3. When the birch stand is 20-25 years old the birches are felled. They will be 8-12 m tall with a dbh of 8 cm. The mean height of the Norway spruce will be 3-4 m. The spruce stand should be thinned to 2000-2500 stems ha-1.

Alternatively, instead of felling all the birches, 600-800 birches ha-1 could be left for 10-15 years. When the birches are finally cut, their mean dbh will be 15-20 cm.