Growth of Silver birch (Betula pendula) & Downy birch (Betula pubescens) established in four different initial densities on one site in central Sweden

Abstract: Nowadays, there is an increased demand for timber resources and more sustainable forest management, starting from the establishment phase of the forest, e.g., planting. Depending on the management goals, number of seedlings planted and thus initial spacing can be adjusted in order not to waste resources. However, there is very little existing knowledge on how different initial spacing arrangements in both Silver birch (Betula pendula) and Downy birch (Betula pubescens) would affect the further development of a stand, with this study being one of the few that comprises such a research question. The main objective of this study was to test different initial square spacings in Silver birch and Downy birch stands and compare their growth dynamics and long-term production. Long-term production of the different treatments was assessed by using the new basal area functions developed for genetically improved birch. In addition, an economic assessment of full rotation projections was done based on standard management. To do the above-mentioned analysis, long-term observational data was compiled, and additional data collected from one growth trial located in central Sweden, in which both birch species were planted in four different square spacings. Besides the above-mentioned simulations, statistical analyses (one-way Anova) were carried out to test the effect of initial spacing on different growth parameters. Statistical analysis revealed that initial spacing had a significant effect on diameter development and height of the living crown for both species and Gini index for Downy birch. Full rotation simulations revealed that the best results in terms of production/economy for both species were achieved from initial spacing of 1.8x1.8 m. The optimal rotation of the 1.8 x 1.8 m treatment was determined to be 48 years for Silver birch and 49 years Downy birch for timber and pulpwood as the main goal respectively. An evident observation that was not tested was the superior growth of Silver birch compared to its counterpart – Downy birch, which was also reflected in the considerably higher production/growth (MAI) (7.13 m3 ha-1 year-1 to 6.63 m3 ha-1 year-1) and better economy (LEV for timber), 34077 SEK compared to 26576 SEK.