Size matters in studies of dead wood and wood-inhabiting fungi

Because biased biodiversity surveys may result in ineffective use of conservation or research resources it is important that measures for biodiversity are accurate. In forest ecosystems wood-inhabiting fungi are an ecologically important species group. We addressed the question whether or not the traditional methodology to survey only coarse woody debris provides accurate estimates of the assemblages of wood-inhabiting fungi or the dead wood itself. In this study, we included all dead wood pieces irrespective of the diameter. Our results showed that the chosen minimum size of studied dead wood pieces has crucial importance for species recordings of wood-inhabiting fungi and for recording the number of dead wood items in boreal forests. Setting the lower limit of surveyed dead wood to 1 cm resulted in the loss of 96 % of the dead wood pieces from the data. Excluding the smallest dead wood resulted in underestimation of the species richness by 10 % and occurrences by 46 %. By setting the lower limit at 5 cm, 24 % of species and 66 % of occurrences would have been lost from the data, including many species considered to be rare. Ordination analysis also showed that the species assembly in the smallest dead wood pieces is distinctive. We conclude that surveying only coarse woody debris may seriously underestimate dead wood amounts as well as species richness and abundance of dead-wood-associated biota.