Preparing the ground for forest planting

The pine weevil (Hylobius abietis) gnaws on the bark of small spruce seedlings, making plantations in western Norway particularly vulnerable to weevil attacks. Here, the weevils thrive especially well, leading to considerable seedling mortality.

To protect the seedlings from weevil damage, they are either treated with the chemical substance Imprid Skog or coated with wax or other types of coverings. Mechanical soil preparation, exposing the mineral soil, also proves effective against weevils. However, this can be challenging to implement along the coast due to steep terrain, lack of specialised equipment, and expertise. Excavators, on the other hand, are readily available in most places.

New research shows that soil preparation using an excavator, combined with effective plant protection, has a positive impact on preventing weevil damage, even in Western Norway.

In collaboration with AT Skog, NIBIO researchers established three experimental fields in the municipalities of Voss and Ullensvang in Vestland county. After planting in the spring of 2020, they explored the growth and survival of spruce seedlings under various combinations of soil preparation using an excavator and plant protection in the form of wax or Imprid Skog.

The conclusion after three years is that the results of soil preparation are promising. Soil preparation, combined with appropriate plant protection, yielded the best results for both growth and survival. While the costs of soil preparation increase with slope and branch quantity after harvesting, the method is worth considering where the terrain is not too steep, and other conditions are favourable.