FO3 Soil preparation

>> Background information

Development

In the majority of all clear felled areas the soil is scarred by machinery to expose mineral soil and thus to accelerate forest regeneration. The forest is then renewed by either planting or seeding. Four types of soil preparation methods are being employed today: harrowing, mounding, scarring and ploughing.

From the 1960s onwards mechanical soil preparation has been a standard practice in forestry. Since 1990 the annual prepared area has varied between 98 000 and 135 000 hectares with no clear trend.

During the past six decades nearly 5 million hectares of clear felled areas have been mechanically prepared. This corresponds to one quarter of the total area of forests on mineral soil. Some peatland forests (spruce and pine mires) have also been treated with soil preparation, but these areas have been small compared to those on mineral soil.

In the 2000s mounding has become the most common soil preparation method in forestry, in 2012 its share of all preparation was 60%. It is a lighter method than scarification and ploughing. Ploughing has been largely given up and the use of scarification and harrowing has decreased in recent years.

Impact on biodiversity

Although the visible traces of lighter soil preparation methods disappear relatively fast there is no comprehensive understanding of the long-term impacts of the different soil preparation practices. One impact that has been observed is the destruction of ground-lying dead wood. The loss of the volume of dead wood in a regeneration areas after scarring can be as high as 80%. Therefore soil preparation has a strong influence on the possibilities to increase the volume of dead wood in commercial forests. The share of ground-lying dead wood of all dead wood in Finnish commercial forests is slightly over 70%.