Comparative studies on the in-ground and above-ground durability of European oak heartwood ( Quercus petraea Liebl. and Quercus robur L.)

The durability of European oak (Quercus petraea Liebl. and Quercus robur L.) is controversially discussed since a long time. While it is classified as a “durable” timber species (durability class 2, according to EN 350-2), results from different studies indicated a lower durability. Therefore comparative studies with sessile oak and English oak were carried out including laboratory resistance tests against different basidiomycetes, soil box tests against soft rot and other soil-inhabiting micro-organisms, as well as in-ground and above-ground field trials at different test sites. Both oak species were rated “non-durable” (durability class 5, DC 5) in soil box tests and in-ground field trials and “slightly durable” (DC 4) in above-ground field trials. Solely results from laboratory tests with pure basidiomycete cultures led to partly better estimates (“very durable” to “moderately durable” DC 1-3), but did not represent the organisms responsible for decay in the field. For oak, EN 350-2 reflects only laboratory results but not the performance of the material in real field situations.