The influence of plant spacing on growth and survival of Scots pine in various habitats during a 40 year period since stand establishment

Abstract

The aim of this research was to characterise the influence of plant spacing on the survival and growth of pines in dry and fresh coniferous forest habitats after almost 40 years since stand establishment. In this study, we compared seven types of spacing, including square, rectangular and triangular configurations, with initial densities ranging from 6944 units/ha to 15 625 units/ha. The research covered two sites where no tending interventions of selective character were performed throughout the growth period. We found that habitat conditions had an influence on tree survival as well as growth in thickness and height in the pine forest stands. In the less fertile habitat, where competition between trees was less intense, about 1,5 to 2 times more trees survived than in the more fertile habitat. Pines growing in the fresh coniferous forest were taller and had substantially larger diameter breast heights (dbh) in comparison to pines of the dry coniferous forest. Additionally, habitat conditions had an influence on the spacing effect correctness of the analysed features. In the poorer habitat this influence was stronger, which showed in a greater differentiation of the analysed parameters as compared to the more fertile habitat. Average dbh values of all trees on the Płock surface increased with decreasing initial density and ranged from 8,24 cm in variant A (15 625 units/ha) to 9,79 cm in variant C (6944 units/ha). On the Łąck surface, trees growing at a lower density (variants C and E) were significantly thicker than trees growing at densities between10 000 units/ha and 15 625 units/ha (spacing variants A, B, F, G). Furthermore, our results showed a significant influence of habitat conditions and plant spacing on the thickness of pines belonging to the 1st biosocial class.

Moreover, we found a positive influence of triangular-shaped spacing on the trees' thickness increment in the fresh coniferous forest, which confirms reports from other authors. Hence, we can deduce that triangular spacing enables trees to make better use of their surrounding space which positively impacts on their growth parameters. Based on these results, we can conclude that, in pine forests, there is a significant influence of habitat conditions on tree survival and growth in thickness and height. This study also showed significant differences between the types of plant spacing and their effect on pine shafts in the II age class. However, a relationship between height growth rate and initial density was not observed. In both of the investigated habitats, the highest trees were observed at densities around 11 500 units/ha with triangular spacing enhancing this effect.