Age and distance effects on the canopy arthropod composition of old-growth and 100-year-old Eucalyptus obliqua trees

Despite the anthropogenically-induced changes to forest tree demographics, few studies have examined the differences in arthropod species composition between the crowns of trees of different ages. We tested for differences in the taxonomic composition of the canopy arthropod faunas of 100 y.o. and old-growth trees, using eight pairs of trees in an Eucalyptus obliqua tall open-forest with a rainforest understorey in the Warra Long Term Ecological Research Site in southern Tasmania and compared these differences to those related to geographic distances. Sticky traps, hanging flight-intercept traps and bark funnel traps were used to sample the canopy arthropods in different placement situations. There were no significant differences between 100 y.o. and old-growth trees at the tree level, but several at the trap and placement levels. Ordination analyses and correlation analyses indicated that high inter-pair variability related to the geographic distance between trees was partially masking tree age effects. The age of E. obliqua does influence canopy arthropod species composition, but this effect was weaker than the geographic effect that was evident in a relatively uniform forest with a maximum distance between trees of only 324 m. This implied high beta diversity in the forest type has implications for the planning of conservation reserves. Further work is needed to see if age effects are stronger in forests of the ages created by silvicultural treatment.