Dead wood in semi-natural temperate broadleaved woodland: contribution of coarse and fine dead wood, attached dead wood and stumps

Dead wood is essential for biodiversity in forests and is therefore often surveyed in conservation inventories. Usually only coarse downed trees (logs) and standing dead trees (snags) are surveyed, but dead wood also occurs on living trees, in stumps, and in fallen branches. Attached, standing (including stumps) and downed dead wood with a diameter of more than 1 cm was surveyed in 25 semi-natural stands of temperate broadleaved woodland dominated by oak in southern Sweden (most trees younger than 70 years but with an older generation of Quercus, and often Corylus scrub). This study is primarily motivated by the rising interest in biofuel harvesting by thinning which will affect dead wood structure in forests, especially the finer dead wood fractions. The sites in this study contained on average 14.3 m3/ha coarse dead wood (defined as wood with a diameter >10 cm), which is more than twice as much as in production woodland. Fine dead wood (diameter 1–10 cm) made up another 12.2 m^3/ha (45% of the total dead wood volume). Of the fine dead wood, on average 20% was oak wood and 71% was wood from other broadleaved trees. The coarse dead wood fraction consisted equally of oak wood (46%) and wood from other broadleaved species (47%). Coniferous wood amounted to 7% (coarse dead wood) or 8% (fine dead wood). The total dead wood volume was dominated by downed (66%) and standing dead wood (22%), while attached dead wood and stumps amounted to smaller fractions (6% each). The total volume of fine dead wood did not correlate with the total volume of coarse dead wood. These results therefore suggest that fine dead wood cannot be predicted from conservation surveys of coarse dead wood. The value for biodiversity of fine dead wood is discussed, and should not be overlooked in conservation work due to the fact that for example, many fungi and insects are associated with it.