Wood density and growth rate of European and hybrid aspen in Southern Finland

Aspen species are mainly used for paper production in Finland. In order to increase the cutting potential, hybrid aspen has lately been planted in southern Finland. In this study we compared the rotation-time-long growth rate and within-stem density distribution of mature European and hybrid aspen. The material consisted of 30 naturally born European aspen trees and 45 planted hybrid aspen trees from southern Finland. From those trees, altogether 225 discs were measured for the ring-width data and 5109 specimens for the basic density data. The results showed that after an initiation phase of 5–10 years, European aspen grows relatively steadily ca. 5–8 mm/a in diameter, until the tree age exceeds ca. 50 years. Thereafter the diameter growth decreases. Hybrid aspen attains the average diameter growth of 10–14 mm/a, at the age of 10–20 years. At the age of 25, the diameter growth has already decreased down to the level of 5–6 mm/a. The within-stem density distribution was more uniform in hybrid aspen. The average basic densities of European and hybrid aspen wood material were 376 and 363 kg/m 3 , respectively.