The objective of the study was to explore the durability of wood exposed above ground, comprising a wide diversity of wood species and treatments and extensive assessment data on wood durability in ongoing long-term testing. Larch species and Scots pine heartwood, two tropical species ntholo and ncurri and a number of treated wood by copper-based formulations and alternatives (silanes, spiroborate esters, epoxidized linseed oil (ELO)-modified, citrus extractives and thermally modified wood) were accessed according to the standard ENV 12037. Molecular methods were employed to identify the variety of fungi in the wood. Siberian larch showed better performance compared to the species grown in Sweden after the first 10 years of exposure. However, despite the origin, the larch wood was decayed to index 4 after 15 to 20 years of exposure. The alternative treatments by silanes, ELO, spiroborate esters, thermally modified wood and wood treated with citrus extract showed diverse results. Thermally modified wood and wood impregnated with silanes reached decay index of 2 after 12 years of exposure. The wood impregnated with ELO and spiroborate esters demonstrated the best performance of the alternative treatments. Although the low retention applied, the high durability of the wood treated with spiroborate esters improved significantly the durability above ground. Median rating of decay for the three commercial products (micronized copper, organic formulation and the reference preservative CCA was still 0 after 17 years of exposure and 0 to 1 after 17 to 20 years in the case of CCA. Obtained DNA data on the fungal diversity in the exposed wood by sequencing techniques and the resemblance between the subjective assessments of wood decay and the identification information obtained by molecular technique was discussed.

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