Tree species and elevation influence the assemblage composition of saproxylic beetles in subtropical forest of east China

The conservation of saproxylic insects and their habitats has caused growing concerns in modern forest management. In order to optimize the conservation strategies, substrate requirements of saproxylic insects should be fully addressed. However, relevant knowledge is still rather poor in subtropical forests. In this study, we tested the effects of host tree species, elevation, snag diameter and canopy cover on the composition of saproxylic beetle assemblages in a subtropical forest of east China. Saproxylic beetle assemblages associated with snags of different tree species were surveyed in two forest types each with different elevation range (low elevation forest, LEF: 400–850 m; high elevation forest, HEF: 950–1200 m). A total of 21,546 individuals belonging to 510 saproxylic beetle species were collected from 87 snags (11 tree species) using flight intercept traps in six periods from May to October 2010. Results indicated that beetle species richness was not significantly different between most sampled tree species. Canopy cover had significant and negative effects on species richness of saproxylic beetles. Comparatively, elevation and snag diameter showed no significant effects on species richness. Canonical correspondence analysis suggested saproxylic assemblages associated with different trees were more similar to each other in HEF than in LEF. Even when snags belonging to the same tree species were examined, beetle assemblage compositions were clearly different between LEF and HEF. Elevation was the most important variable affecting assemblage composition. Relatively, the effect of tree species on assemblage of saproxylic beetles was more pronounced in LEF. Furthermore, there was a significant linear increase in proportions of generalist species collected from each snag with elevation. More beetle species preferring to live in LEF were prone to develop a narrower host use range than those living in HEF. To conclude, our results demonstrate that the availability of sun-exposed habitat patches in subtropical forests is important to maintain saproxylic beetle diversity. Increasing tree-species diversity is important to increase saproxylic beetle diversity in managed and plantation forests of subtropical China, and appears to be particularly important in low elevation forests.

► Species richness was not significantly different between most sampled tree species.
► Canopy cover had a significant negative effect on species richness.
► Elevation had a strong effect on assemblage composition.
► Effect of tree species on assemblages was more pronounced in low elevation forest.
► Host specificity of saproxylic beetles declined with increasing elevation.