Growth and management of Silver birch and Hybrid aspen in southern Sweden

Abstract: Nowadays, the changing climate and the risks associated with it urge us to re-evaluate our silvicultural practices. Due to the increasing demand for wood and good economy amongst other factors, Swedish forest landscape is dominated by two species – Norway spruce Picea abies (L.) Karst. and Scots pine Pinus sylvestris (L.) However, there are other species such as silver birch Betula pendula Roth and hybrid aspen Populus × wettsteinii Hämet-Ahti = P. tremula L. × P. tremuloides Michx. – two of the fast-growing tree species in Baltic sea region, including Sweden, that may complement the species composition in Sweden, providing various benefits, especially in the face of the changing climate. The main objective of the thesis was to evaluate the early growth of silver birch and hybrid aspen depending on the management done so far. Also, to assess the growth and economy of full rotation birch stands in southern Sweden using a standard management regime. Data was collected from four experimental sites located in southern Sweden established on both forest land and agricultural land. Different functions were applied to estimate both early growth, e.g. height, basal area, volume, as well as future growth and development of silver birch stands. A statistical model was constructed to test the effect of fertilization. Genetically improved silver birch (Ekebo 4) showed comparable growth next to hybrid aspen which is proved as one of the fast-growing tree species in Sweden. Statistical analysis revealed that fertilization has a significant effect on all growth parameters tested (height, DBH & volume) of both species, with differences between fertilized and unfertilized values being larger for hybrid aspen. Simulations of full rotation stands of silver birch showed that optimal rotation length of birch stands planted with improved material is between 36 – 40 years, while mean annual increment varies from 9.2 – 13.3 m3 ha-1 year-1 with the best performance delivered by birch planted on agricultural land.