Using soil and litter arthropods to assess the state of rainforest restoration

Abstract

The present study investigated recolonization patterns of selected soil and litter arthropods following replanting of pasture with rainforest species in the Mary River catchment of eastern subtropical Australia. While extensive research has been conducted in rehabilitated mined sites in Australian dry sclerophyll forests, very little attention has been paid to rainforest restoration on previously pastoral land. We examined the utility of soil and litter arthropod groups for monitoring the progress of restoration, and the relationship between arthropod assemblage patterns and environmental factors potentially under the control of those doing the replanting. Leaf litter was extracted from 20 sites: five remnant rainforest, five pasture, and 10 sites that had been revegetated (from 1 to 12 years previously) with a diversity of indigenous species. Ants (identified to genus), centipedes, millipedes, isopods, amphipods and mites were enumerated and their assemblages described with multi- and univariate methods. Ant genera alone proved unable to distinguish pasture from rainforest, and mites (identified only to oribatid or non-oribatid) proved of limited use because these two groups were present in all samples in extremely high numbers that overwhelmed the contributions of other arthropod groups. However, a coarse taxonomic approach using five arthropod groups (ants, centipedes, millipedes, isopods, amphipods) clearly discriminated between pasture and rainforest, and also arranged the revegetated sites between these two extremes. Simple frequency scores based on the presence/absence of these arthropod groups in each of three replicate subplots were sufficient to achieve this separation of site types. Habitats created by close planting of trees and mulching may accelerate invertebrate colonization and, thus, promote the rapid establishment of processes and functions characteristic of developing rainforests.