Translocating deadwood in ecological compensation benefits saproxylic beetles, but effects are dependent on substrate density

Ecological compensation is increasingly used to offset habitat and biodiversity loss resulting from changes in land use, large infrastructure projects (e.g., roads and railroads) or industrial expansions (e.g., mines, harbours), but the effectiveness of specific compensation strategies remain largely untested. When old-growth forest ecosystems are impacted by such projects, designated compensation areas may also require additional restoration or habitat enrichment. For organisms that rely on habitats that require decades to develop, such as advanced decayed wood, restoration will require novel approaches. We tested whether translocation of deadwood of various decay stages and large dimensions enhance saproxylic beetle communities within compensation areas in a large boreal forest landscape in Sweden. Experimental plots (50 m in diameter) within the compensation zone were enriched with 0, 16, or 48 deadwood substrates. We collected beetles using flight intercept traps prior to translocation and again 1 and 4 years after translocation and compared species richness, abundance and assemblage composition across treatment and over time. We showed that translocation of relatively high densities of deadwood (48 substrates per plot) increased species richness of saproxylic beetles. Increased beetle richness could have occurred from direct transport of beetles in experimental substrates and/or through attraction of beetles to the translocated substrates. Our results indicate that translocation of deadwood can serve as an important tool in ecological compensation and restoration if sufficient amounts of deadwood are translocated. While promising, the long-term success of restoring saproxylic biodiversity through translocation of deadwood depends on whether translocated substrates continue to provide suitable habitat for beetles over time and whether benefits for biodiversity can be enhanced through targeted translocation of specific combinations of deadwood.