Saproxylic beetles in Populus tremula fauna depots - how do you construct the best depot?

Abstract: The biodiversity of saproxylic organisms and in the case of this study, saproxylic beetles, is dependent on the amount and quality of course woody debris (CWD) in the environment. Over the past decades the quantity of CWD in Swedish forests has increased, yet the quality has decreased, forests are managed and exploited, and old-growth forests are rarer. To counteract this, fauna depots, artificial piles of dead wood, can be placed to increase the amount and quality of habitat for saproxylic organisms. This study measured fauna depots of aspen CWD placed in Uppsala municipality to find which combination of qualities resulted in the highest species richness and abundance (diversity). A total of 242 beetles across 26 species were sampled using a bark sifter and Tullgren extraction funnels. The CWD qualities; number of logs, log diameter, sun exposure and decomposition level were measured. Log diameter was confirmed to be positively correlated with species richness supporting previous research. Decomposition was also positively correlated with species richness, but this not supported by previous research. Some qualities, like sun exposure, were unexpectedly not correlated and number of logs was negatively correlated. Only one red-listed species was found across all samples. Overall results were somewhat inconclusive but provide hints towards better practice in saproxylic beetle conservation, such as placing larger logs in the depots.