Mechanizsed microsite preparation and direct seeding of Pinus sylvestris in boreal forests — a way to create desired spacing at low cost

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The main objective of this study was to examine the cost, flexibility, and appropriate scale of mechanized microsite preparation (MP), in combination with mechanical direct seeding of Pinus sylvestris L. with orchard seed. This technique was tested at four boreal forest sites in Northern Sweden. Orchard and stand seeds were sown with and without MP. The use of orchard seed increased seedling establishment by 41% and the use of MP increased seedling establishment by 47%, respectively, after two years. The best substrates for sowing when using MP were OAh-, E- and BC-horizon, in ranked order. The use of orchard seed compared to stand seed increased mean seedling height by 25% after four years. These trials suggest that to obtain a density of 5,000 stems ha-1 four years after seeding, 61,000 viable stand seeds or 41,000 orchard seeds ha-1 should be sown if MP is not used. If MP is used, seeding rate could be reduced by about 32%. By using MP, and by further improving scarification technique so that all scarified area is thin OAh-horizon, we predict that only 32,000 stand seeds or 22,000 orchard seeds ha-1, i.e., half the dosage, should be needed. Under these optimal conditions, it would be necessary to sow about six and four germinable stand and orchard seeds, respectively, to ensure one seedling after four years. Furthermore, regeneration cost would be less than a third that of planting.