Moss invasion in a dune ecosystem influences ground-dwelling arthropod community structure and reduces soil biological activity

Abstract

One of the most invasive moss species worldwide is Campylopus introflexus, which can change vegetation and habitat conditions of native ecosystems (dunes, heathland). However, the impact of the moss on the community structure of multiple arthropod taxa and ecosystem functions is still poorly understood. For a better understanding of impacts of invasive species, scientific studies are needed which explicitly define the investigated impact. We defined impact based on the most recently recommended categories: ‘directionality’, ‘classification and measurement’, ‘ecological or socio-economic changes’, and ‘scale’. We investigated the impact of C. introflexus on a wide range of ground-dwelling arthropods (pitfall traps) and on soil biological activity (bait-lamina test) by comparing invaded and uninvaded grey dunes in a field observational study on the island of Hiddensee, Germany. We found that the moss and the associated habitat modifications influenced the arthropod community structure. The effects on arthropod densities were taxon-specific and were positive (Coleoptera, Formicidae, Opiliones) or neutral (Araneae, Orthoptera). For Collembola and Isopoda we assumed an indirectly negative effect of the moss due to associated lower field layer cover and soil moisture. C. introflexus drastically reduced the soil biological activity, which was about six times lower in invaded grey dunes. The reduced soil moisture associated with the moss invasion was identified as the main driver of the shifts in community structure and soil biological activity. By explicitly defining ‘impact’ in our study, we add to recent discussions within invasion ecology about invasive species impacts. Our study demonstrates the importance of cross-taxon approaches which include key ecosystem processes such as soil biological activity and therefore contributes to the progress towards the general understanding of plant invasion impacts.