Fine woody debris is important for species richness on logs in managed boreal spruce forests of northern Sweden

Species richness of wood-inhabiting cryptogams was compared on fine woody debris (FWD; diameter 5-9 cm) and coarse woody debris (CWD; diameter =,>10 cm) logs of Picea abies (L.) Karst. Data were collected from managed boreal forests of northern Sweden. Species richness was higher on CWD than FWD when equal numbers of logs were compared. When equal surface areas were compared, species richness on FWD and CWD did not differ. When equal volumes of CWD and FWD were compared, FWD had more species. This was an effect of surface area and log quantity, as a certain volume of FWD was composed of more logs and had greater surface area than the same volume of CWD. We varied woody debris volume and proportion of FWD in a simulation model of species richness on logs. At low volumes of woody debris, species richness increased with the proportion of FWD. At higher log volumes, species richness increased with the proportion of CWD. In managed forests where there are small amounts of woody debris, FWD is important for the total species richness on logs and should not be neglected despite the fact that species richness is generally positively correlated with log diameter.