Dry rainforests have a distinct and more diverse assemblage of epigaeic invertebrates than eucalypt woodlands : implications for ecosystem health monitoring

Dry rainforests have a disproportionately higher diversity of plant species than the eucalypt woodlands that dominate Australian landscapes. While several endemic vertebrate species have been found in dry rainforests, their values for invertebrate fauna are relatively poorly known. Epigaeic invertebrates of four patches of dry rainforests in Queensland were annually compared to those of nearby eucalypt woodlands using pitfall traps between 1998 and 2002. Dry rainforests had significantly greater Order-level richness, lower dominance, fewer invertebrates and a different assemblage. Invertebrate composition was characterized by typically shelter- or moisture-requiring taxa, such as earwigs, pseudoscorpions, gastropods, millipedes, isopods, Diplura and Symphyla. This may reflect the greater prevalence of moister microhabitats in dry rainforests in comparison to woodlands. Coinciding with several years of low dry season rainfall, invertebrate abundance declined in dry rainforests but not woodlands, indicating that dry rainforest epigaeic fauna may be more sensitive to reduced soil moisture compared with woodland fauna. This may reflect differences of some taxa in evolutionary lineage or the mediation of vegetation phenology and differences in drought susceptibility of the two vegetation types. Importantly, the study provides evidence that faunal assemblages of drier rainforests may be more vulnerable to tipping points associated with droughts and changing rainfall regimes than nearby woodlands. Furthermore, it demonstrated the importance of including a range of vegetation types in any long-term monitoring programs and that an understanding of ecological responses to environmental drivers is critical to interpreting data. The relatively greater sensitivity of dry rainforest biota to droughts compared with woodlands indicates that it could provide a regional "control" for this effect.