Effect of size and shape of specimens on the mass loss caused by Coniophora puteana in wood durability tests

The experimental basis for testing the biological durability of wood often includes incubation experiments with wood-destroying basidiomycetes. Numerous parameters can affect the mass loss by fungal decay (ML_F) in laboratory durability tests and therefore being decisive for the resulting durability classification. Among others, the dimension of the wood specimen and the time of incubation impact on fungal decay. Hence, both parameters were examined within this study using 19 different specimen formats and four different incubation times. Specimens of larch heartwood (Larix decidua Mill.) were incubated with pure cultures of the brown rot fungus Coniophora puteana. Scots pine sapwood (Pinus sylvestris L.) was used as a reference. The wood specimens’ format turned out to significantly affect both mass loss by fungal decay (ML_F) and resulting x-values when ML_F of larch was compared with that of the reference Scots pine sapwood. Both measures were highest for specimen formats with moderate surface-volume ratios. ML_F and x-values depended on specimen size and shape as well as on the time of incubation. Reducing the specimen volume generally led to higher ML_F at a given incubation time, but prolonging incubation times led to higher x-values and thus to lower durability expressed as durability classes (DC). In summary, it appeared highly questionable that results of basidiomycete durability tests can be easily compared to each other when specimen format and/or incubation time deviate from the standard conditions.