Covering up for Scots pine seeds

Direct seeding of Scots pine is a popular forest regeneration method in Finland, accounting for 20% of the total regeneration area annually. On most sites, direct seeding is done mechanically, i.e. in combination with soil scarification. The most common soil scarification method is disc trenching. Also patch scarification either with two row Bracke-mounder or excavator is used in Southern Finland. After mechanical direct seeding, many seeds remain visible on the top of the exposed mineral soil for a while. This exposes seeds to predation and drying. Partly because of this, final seedling establishment is usuallly relatively low (10-20 %). The aim of the research now conducted in the Natural Resources Institute (LUKE), Finland, is to improve seed cover also in mechanical seeding.

Utilizing soil erosion

The first experimental method is based on the occurrence of soil erosion on the surface of the seedbed soon after scarification. To achieve controlled covering of the seeds due to soil erosion, a special blade was designed to create shallow furrows and pits on the surface of the seedbed. The blade was manufactured by Swedish company Bracke Forest and it was attached to a two-row Bracke mounder equipped with TTS Sigma seeding device. A test-drive on forest regeneration area showed that the new scarification blade worked as planned. The surface of the seedbed was quite different compared to the old blade, which is normally used in scarification of direct seeding areas. Unfortunately, due to defects in the seeding device, we were not able to get results concerning the seedling establishment yet. However, we will continue the testing next spring. Some small modifications will also be made to the blade.

Direct covering

The second method is to try to cover the seeds directly. For this a special excavator bucket with rotary screen and an integrated electrical seeding device was designed . The bucket was constructed by Finnish company Vipermetal / Ajutech. In this method a shallow mineral soil patch is first made with the edge of the bucket. Then seeds are sown on the surface of the patch and finally, the rotary screen is used to cover seeds with a thin soil layer. In general, the latter method had a positive effect on seedling establishment. However, it was discovered that the thickness and composition of the cover had a great impact on establishment. The best result was achieved with very thin (approximately 1 cm) layer of humus and/or small particles of ground vegetation (moss, lichen etc.). Instead mineral soil layer exceeding two centimeters in thickness slowed down seedling emergence considerably or prevented it completely. Thus, care must be taken when the screen is used to cover seeds. The bucket can also be used for mounding and ditching if necessary.