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The influence of initial spacing on growth and survival of Scots pine in 40 years period of cultivation in varied habitat conditions

Abstract The aim of the research was to determine the effect of initial spacing on the survival and growth of pine trees in dry coniferous and fresh coniferous forest habitats after nearly 40 years from the establishment of plantation. The study presents an analysis of seven spacing variants in square, rectangular and triangular spacing patterns with the initial density ranging from 6 944 seedlings/ha to 15 625 seedlings/ha. The studies were conducted on two study sites. No tending treatments (selective thinning) were performed in the examined stands throughout the growing season. It was shown that habitat conditions had a significant effect on the survival, diameter and height growth of trees in pine stands. In the less productive forest habitat, where the competition of trees is smaller, the survival was 1.5 to 2-fold higher compared to the more productive habitat. Pine trees growing in the fresh coniferous forest had substantially larger diameters at breast height (dbh) compared to the dry coniferous forest. The spacing effect depended on the habitat conditions. This influence was stronger in the less productive habitat compared to the more productive forest habitat which was reflected in the greater differences in the discussed parameters. The average dbh value of all trees on the Płock site increased with the increase of tree growing space (i.e. lower initial planting density) and ranged from 8.24 cm in variant A (15 625 seedlings/ha) to 9.79 cm in variant C (6 944 seedlings/ha). On the Łąck site, the trees growing at a low density (variants C and E) had significantly larger diameters compared to the trees growing at a density from 10 000 plants/ha to 15 625 plants/ha (spacing variants A, B, F, G). The studies also showed a significant effect of the habitat conditions and initial spacing on the diameter of pine trees in biosocial class I. Triangular spacing in the fresh coniferous forest was found to have more positive effect on tree diameter growth. It is consistent with the findings of other authors that trees planted in triangular spacing make better use of space which is positively reflected in their growth. The results obtained from the research allow to formulate the conclusion that habitat conditions have a significant effect on the survival, diameter and height growth of trees in pine stands. The research also showed a significant effect of initial spacing on the diameter at breast height of pines at the end of age class II. No dependence was found of the initial planting density on the height growth rate of trees. In both forest habitats under consideration, trees planted at a density of approximately 11.5 thousand plants per hectare were the highest. The triangular initial spacing pattern had a positive effect on this characteristic.