Finnish Forest Research Institute  Metla

Press release 15.8.2006

Clone research: Fast growth rate reduces wood density and strength properties of Norway spruce

The effects of growth rate on the wood density and strength properties of Norway spruce cutting clones were studied in a collaboration project of Metla, the University of Helsinki and VTT (Technical Research Centre of Finland). The results of the study performed on three different sites located within the boreal zone indicate that the wood density and mechanical strength properties were best in areas where the growth rate was slowest.

The rooted cutting clones were planted in the 1970s on different sites differing in nutritional and soil properties. The target sites were located in Loppi (site 1), Imatra (site 2) and Kangasniemi (site 3). The first two sites were nutrition-rich, former agricultural land, while the third site represented the drier Myrtillus-type forest land.

At the time of felling the tree height was almost 13 metres in Loppi and Imatra. In Kangasniemi the trees were less than ten metres high. The trees in Kangasniemi had been planted a couple of years later than on the other two sites, but the trees were still shorter than would have been expected on the basis of the younger age. The mean annual ring width was also shown to be narrowest in Kangasniemi, so the overall growth rate was concluded to be slower in Kangasniemi than on the other two sites. Soil nutrition was shown to increase growth rate on the other sites.

The Kangasniemi site produced trees with higher wood density than the trees grown on the nutrient-richer sites. Also the strength properties of these slow-growth trees differed favourably: their mean modulus of elasticity and rupture were greater than those of trees grown on test sites that produced fast-growth trees.

Three different clones were planted in different soil-type areas. The results showed that the differences between the clones were similar for all of the sites: the fastest growing clone C was fastest on all sites, which indicates that clone-to-clone variation was not affected by the site. At the same time, the wood density of clone C was lower than that of the other clones. The wood density of the slowest-growing clone B, however, was highest. The environment had an effect on growth as well, because the growth of all clones was slower in Kangasniemi than on the other two sites containing more nutrients. However, there were significant seasonal differences as well, both in the annual ring and wood density. Marked variation was found between trees as well.

Publication: Sanni Raiskila, Pekka Saranpää, Kurt Fagerstedt, Tapio Laakso, Mia Löija, Riitta Mahlberg, Leena Paajanen & Anne-Christine Ritschkoff. 2006. Growth rate and wood properties of Norway spruce cutting clones on different sites. Silva Fennica 40(2): 247–256.

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