Browsing by Author "Sutela, Tapio"

The Siberian larch (Larix sibirica Lebed.) is, as a deciduous conifer, a rarity in Finnish forests. The natural resistance to decay of its heartwood is one of the most highly valued characteristics of the Siberian larch, thanks to which it is often favoured in humid environments in water and earth construction projects. Resistance to decay is often related to logs and wood products from the last stages of the life cycle of a commercial forest. The objective of this study was to examine the natural resistance to decay of the heartwood of 25-year-old Siberian larch. A ground contact decay resistance test in compliance with the EN 252 standard was carried out at the Punkaharju unit of the Natural Resources Institute Finland in Savonlinna, Finland. The main data consisted of 25-year-old Siberian larches thinned from clonal seed orchard sv356 in Neitsytniemi, Imatra, Finland. The clonal seed orchard has been established using seedlings from 25 mother plants, the plus trees of which grow in Lapinjärvi, Punkaharju and Ähtäri, Finland. The plus trees originate from Raivola larch stand. The reference material used in the ground contact test was the heartwood of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and high-density heartwood of older Siberian larch. The field test was commenced in September 1996. The progress and impacts of decay were monitored by means of a visual inspection of test stakes (n=377) and bending test if required in the autumn, to determine the decay rate of the test stakes and test groups. Test stakes broke in the bending test due to decay-related weakening of the wood. The service lives of various test stakes and test groups were determined on the basis of the time of breaking of the wood. As the test ended in June 2015, measurements had been made in a total of 12 years. The one-way repeated measures ANOVA was used to measure the rate of decay in test groups. The service lives of the test groups were analysed using the Kaplan-Meier survival analysis and the log-rank test. Test stakes from both Siberian larch test groups remained unbroken throughout the test. All test stakes from the reference groups of Scots pine and Norway spruce broke during the test. The examination of average heartwood decay rates between test groups showed a lower average heartwood decay rate for the heartwood of the 25-year-old Siberian larch than for Norway spruce heartwood. The decay rate was the same as for Scots pine heartwood. The average decay rate of the older and dense Siberian larch heartwood was lower than that of the other three groups. The average service life of 25-year-old Siberian larches was a minimum of 9 years and 7 months, whereas the average service life of Scots pine was 7 years and 7 months, and that of Norway spruce 5 years and 8 months. The service life of the older and dense Siberian larch was a minimum of 16 years. The plus tree stands of the 25-year-old Siberian larches that remained unbroken throughout the tests were located in Punkaharju and Ähtäri. The average decay rate of clones from the Punkaharju was lower than that of test stakes from Ähtäri or Lapinjärvi. The difference between the service lives of clones was statistically significant. The shortest service life was 6 years and the longest 12 years. The service life of clones originating from the plus trees from the clonal seed orchards of Punkaharju and Ähtäri was statistically significantly longer than that of clones from Lapinjärvi. A conservative interpretation of the results would indicate that the decay resistance of the Siberian larch seems to be better than that of Norway spruce. Compared to Scots pine, the decay rate improves as the Siberian larches age. Variation was found in the decay resistance of 25-year-old Siberian larches both between clones and between plus tree stands. The area of origin of the plus trees of the clones had a significant impact on decay resistance.