Early seedling growth of Pinus sylvestris after sowing with a mixture of stand and orchard seed in dense spacings

Effects on early seedling growth of seeding stand and orchard seed of Pinus sylvestris L. in different mixtures (100, 75, 50, 25, and 0% of orchard seed) at 4-cm target spacing were quantified in one nursery and one field experiment during a 2- and 5-year period, respectively. In the field experiment, 50% mixtures at 8- and 12-cm target spacing were also studied. Seedlings from orchard seeds (OS) had in general higher growth rate than seedlings from stand seed (SS). In the nursery experiment, OS were 25% taller, had 41% larger above-soil biomass, and 18% larger root biomass than SS after 2 years when sown separately. However, root/shoot ratio was 26% less and the slenderness value (height/diameter ratio) was 11% greater for OS in comparison with SS. Stand seed in high competition, compared with low competition (mixture 75% vs. mixture 0%), were 11% taller, had 15% greater slenderness value, and 25% less root biomass after 2 years. OS had 9% greater slender value in mixture 100% compared with the 25% mixture. In the field experiment, the tallest OS in each plot were 22% taller and the largest OS had 103% larger stem volume than the tallest or largest SS when sown separately after 5 years. After a height-selection thinning to one seedling per plot at year five, 79% of the seedlings in 50% mixtures would be OS. Seedlings sown in 12-cm spacing were 69% taller and had 527% larger stem volume than seedlings in 4-cm spacing after 5 years. The investigation supports that orchard and stand seed could be direct seeded in a mixture. Low dosages of the more expensive orchard seeds could be used to obtain growth advantages. Stand seeds should be added to increase the number of seedlings to the desired spacing.