Changes in strength of Scots pine wood (Pinus silvestris L.) decayed by brown rot (Coniophora puteana) and white rot (Trametes versicolor)

•The initial stage of fungi development influences wood strength properties.•Different rate for white- and brown-rot were found.•Decrease of strength properties was quantified.•Brown-rot causes more drastic decrease of wood strength. Alterations in static bending strength, compressive strength parallel to the grain and the modulus of elasticity (MOE) of Scots pine (Pinus sylvestris L.) wood decayed by the white-rot fungus (Trametes versicolor) and the brown-rot fungus (Coniophora puteana) were investigated. The drastic decrease of the bending strength was observed for the initial phase of the decay and the changes were exponential. A 50% decrease in the property was found for 7% of mass loss in the case of brown rot and 20% for white rot. A linear decrease in compressive strength was observed with an increasing mass loss. White rot caused a 50% decrease of compression strength for the mass loss of ca. 30%, while for the brown rot the same decrease was observed for 20% of mass loss. The slowest linear changes were observed for the modulus of elasticity (MOE). In the case of white rot the MOE values were reduced by ca. 50% for a mass loss of 40%, while for brown rot a 50% decrease in the property was found in a mass decrease as low as 20%.