Combinations of aggregated and dispersed retention improve conservation of saproxylic beetles in boreal white spruce stands

Retention of living trees in harvested stands is widely promoted as a way to conserve forest biodiversity; however, the quantity, quality and distribution of retention required to best meet biodiversity conservation goals are uncertain. We compared saproxylic beetle assemblages in dead white spruce among two sizes of retention patches (0.20 ha and 0.46 ha) surrounded by three different levels of dispersed retention (2% = clearcut, 20%, and 50%) in 10 ha cut-blocks included in the EMEND (Ecosystem Management Emulating Natural Disturbance) experiment in northwestern Alberta, Canada. Significant blow-down in forest patches of these sizes appeared to reduce their conservation capacity for saproxylic beetle assemblages 10-11 years post-harvest. However, higher amounts of dispersed retention in the matrix surrounding patches increased their capacity to maintain saproxylic beetle assemblages in comparison to clearcuts. Predatory species were most sensitive to harvesting intensity in the surrounding matrix. Our data suggest that ecosystem-based management that leaves combinations of aggregated and dispersed retention has much potential for conservation of saproxylic beetles.