Succession of saproxylic beetles associated with decomposition of boreal white spruce logs

Abstract

We reared saproxylic beetles from 54 white spruce [Picea glauca (Moench) Voss] logs collected in northwestern Alberta, Canada. Logs represented six decay classes, ranging from freshly dead to well decayed. Beetle assemblages were indicated mainly by phloeophagous and predaceous species in early decay stages, although indicator species were mainly predaceous in later stages of decay. No indicator species were identified for intermediate decay stages. Larvae from rearings were disproportionately predaceous. Thus, movement of juveniles within and among coarse woody debris (CWD) substrates is likely an important aspect of the life history for these species. Beetle assemblages changed progressively with increasing stages of decomposition. Assemblages of adjacent decay classes were highly similar, although similarity decreased with increasing difference in decay classes. Therefore, the retention of all decay classes of white spruce downed CWD on post-harvest landscapes is necessary to conserve the associated saproxylic beetle fauna. Retention of CWD in advanced decay stages, which contains species not found in earlier decay classes, presents a particular challenge in forest management because of the long times required to develop CWD in the later stages of decomposition.