Mechanized seeding in conjunction with disc trenching has increased in popularity in Finland during the past few years. Mechanization is, in turn, expected to increase the popularity of seeding, especially on the less-fertile sites. The present study also addressed the issue of application possibilities for seeding and natural regeneration in combination and separately.
When applying natural regeneration, the emphasis should be on good seed years or the time immediately prior to such years. At other times regeneration may extend over an unreasonably long period of time and the increment represented by seed-bearers will not be sufficient to compensate for the losses resulting from the lengthy restocking period. On poor soils, the site preparation trace appears to retain its seed-bed property for three years, but restocking should be achieved immediately following site preparation (or at least during the following growing season) in order to prevent competing vegetation becoming a problem. Since the seed crop varies greatly from stand to stand, it is best to check at amount of the cone crop case by case before deciding in favour of natural regeneration. Cone crop forecasts are of help when making preparations for natural regeneration.
The point in time when seed are shed varies greatly due to weather conditions. If the purpose is to make use of most of the seed crop, site preparation should be carried out before the 15th of May. Nevertheless, site preparation done towards the end of May also gave unexpectedly good results.
In poor seed years it is best to resort to direct seeding. This is particularly so if the lack of female inflorescences gives grounds for assuming that the next year will also be a poor seed year. In good seed years natural regeneration is equal to direct seeding. If one is uncertain as to the sufficiency of natural seeding, one can supplement it through direct seeding (but the amount of seed required is less than in normal seeding). Supplementary seeding is particularly appropriate when applied mechanically using a machine as the labour costs are small. It is also possible to combine seeding by the adjacent stand and direct seeding and thereby achieve lower costs by reducing the amount of seed sown in the vicinity of the adjacent stand's edge. In good seed year, small restocking sites surrounded by standing forests restock without supplementary action.
Key words: Pinus sylvestris, natural regeneration, seed crop, seeding by adjacent stand.
Correspondence: Kaarlo Kinnunen, Finnish Forest Research Institute, Parkano Research Station, FIN-39700 Parkano, Finland
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