Early colonization of white spruce deadwood by saproxylic beetles in aggregated and dispersed retention

Retention harvests may leave retention in aggregations, evenly dispersed, or in various combinations. Although the relative efficacy of aggregated and dispersed retention for biodiversity conservation is widely debated, there has been little study of combinations. We studied this question relative to saproxylic beetles that initially colonize horizontal and upright coarse woody material (CWM) of white spruce in boreal mixedwood stands at the EMEND (Ecosystem Management Emulating Natural Disturbance) in northern Alberta 12-13 years after retention prescription. Neither species richness nor emergence of beetles differed among freshly cut bolts exposed as 'horizontal' or 'upright' in retention patches of two sizes (0.20 ha and 0.46 ha) that were surrounded by different levels of dispersed retention (2%, 20% and 50%). However, species composition in retention patches differed significantly from those in unharvested controls, except in the larger patches surrounded by 50% dispersed retention, although patterns differed among feeding guilds. Both mycetophage and predator assemblages in patches were similar to those in unharvested controls, suggesting that even relatively small patches retain these guilds regardless of the surrounding matrix quality. Because species composition differed between horizontal and upright bolts, an appropriate mix of horizontal and upright CWM may contribute to conservation of saproxylic beetle faunas.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author