Effects of Greenfall on Ground-dwelling Arthropods in a Subtropical Forest

Resource events such as typhoon-triggered greenfall have consequences for multiple ecological mechanisms, ranging from population dynamics and trophic interactions to ecosystem processes. Arthropods are sensitive to environmental disturbances, and many taxa have been used as indicator species. In a field experiment, we tested the effects of greenfall on ground-dwelling arthropods (mostly litter-dwelling taxa) in a forest of Taiwan red pine (Pinus taiwanensis) in the summer of 2013. Of 20 field plots (5 x 5 m), half received P. taiwanensis greenfall while the other half served as unaltered controls. As predicted, some arthropod taxa responded more strongly than others to the greenfall addition. Among the examined arthropod taxa (Araneae, Coleoptera: Carabidae, Coleoptera: Staphylinidae, Hymenoptera: Formicidae, Collembola, Isopoda: Oniscidea), the predatory staphylid beetles (Staphylinidae) responded positively to greenfall addition while the larger-sized detritivore woodlice (Oniscidea) responded negatively. Contrary to our prediction of a positive response, the smaller-sized detritivore springtails (Collembola) were unaffected by the greenfall addition. At the beginning of this study, we observed short-term effects of a naturally-occurring typhoon, to which springtails and ants (Formicidae) responded negatively while staphylid beetles responded positively. Also contrary to our prediction, these taxon-specific responses did not suffice to alter the composition of arthropod communities. We concluded that the intra-annual effects of typhoons-specifically those associated with greenfall-are more likely to impact certain taxa, including staphylid beetles, woodlice, springtails and ants. At the taxonomic level examined here, these intra-annual effects on community composition are non-detectable. As typhoon frequency and intensity are likely to change with global warming, the study makes a timely contribution to our understanding of typhoon-induced ecological dynamics in subtropical plantation forests.