Abstract
Riparian zones are complex, dynamic habitats that play a critical role in river ecosystem functioning. Terrestrial invertebrates comprise much of the diversity found in riparian habitats and facilitate the transfer of energy between aquatic and terrestrial systems. However, the consequences for terrestrial invertebrates of invasion of riparian zones by invasive non-native plants (INNP) remain poorly understood. Responses of terrestrial macroinvertebrate morphospecies to invasion by two common INNP, Fallopia japonica (Japanese knotweed) and Impatiens glandulifera (Himalayan balsam) were assessed, relative to local environmental factors. Terrestrial invertebrates were collected from 20 sites on low order streams in June and August alongside data on physical attributes and land use. Greater cover of F. japonica and I. glandulifera cover reduced total invertebrate abundance and morphospecies diversity at the individual sample scale, whilst increasing spatial heterogeneity of invertebrates at the site scale. Impatiens glandulifera reduced morphospecies diversity at the site scale with increasing cover, but this was not observed for F. japonica. INNP affected terrestrial invertebrate morphospecies abundance and diversity, to a greater extent than prevailing environmental conditions. Our findings therefore offer support for managing riparian plant invasions to improve habitat heterogeneity, restore terrestrial invertebrate diversity and repair aquatic-terrestrial linkages.
Highlights
Terrestrial invasive non-native plants (INNP) represent over 300 of the established plant species in Europe (Keller et al 2011)
Our results indicate that the focal INNP species reduced the diversity and abundance of terrestrial invertebrates at heavily invaded sites
INNP were associated with reduced terrestrial invertebrate morphospecies abundance and both alpha and gamma diversity
Summary
Terrestrial invasive non-native plants (INNP) represent over 300 of the established plant species in Europe (Keller et al 2011). INNP are often associated with reductions in overall biodiversity (Barney et al 2015), lower abundance of terrestrial primary consumers (McCary et al 2016) and disruption of above and below-ground fungal communities (Pattison et al 2016). Negative impacts on ecosystem services such as pollination and biomass production may be associated with INNP (Hulme et al 2013), alongside altered rates of erosion and water use compared to their native counterparts (Pejchar and Mooney 2009). Impacts on ecosystem services and biodiversity comprise some of the main criteria for listing a species as an invasive alien species (IAS) under EU regulation No 1143/2014, which covers the prevention, management and spread of IAS (European Union 2014). Societal reactions to IAS may depend on visible effects of visible invaders (Simberloff et al 2013), which may hinder restoration efforts following colonisations by less prominent IAS
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