Abstract
Riparian zones form the interface between stream and terrestrial ecosystems and play a key role through their vegetation structure in determining stream biodiversity, ecosystem functioning and regulating human impacts, such as warming, nutrient enrichment and sedimentation. We assessed how differing riparian vegetation types influence the structural and functional composition (based on species traits) of stream invertebrate communities in agricultural catchments. We characterized riparian and stream habitat conditions and sampled stream invertebrate communities in 10 independent site pairs, each comprising one “unbuffered” reach lacking woody riparian vegetation and a second downstream reach with a woody riparian buffer. Forested riparian buffers were associated with greater shading, increased gravel content in stream substrates and faster flow velocities. We detected changes in invertebrate taxonomic composition in response to buffer presence, with an increase in sensitive Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa and increases in key invertebrate species traits, including species with preference for gravel substrates and aerial active dispersal as adults. Riparian vegetation independently explained most variation in taxa composition, whereas riparian and instream habitat together explained most variation in functional composition. Our results highlight how changes in stream invertebrate trait distributions may indirectly reflect differences in riparian habitat, with implications for stream health and cross-ecosystem connectivity.
Highlights
The habitats that form the interface between a stream and its adjacent terrestrial landscape are known as “riparian zones” [1]
The two axes in both plots clearly reflected gradients related to changes in the riparian characteristics and vegetation cover between study reaches, with buffered reaches correlated with riparian buffer size and percentage of canopy cover and plant litter, as well as instream CPOM
The higher abundances of active aerial dispersing stream insects in the buffered reaches suggested that cross-habitat connectivity with riparian food webs could be strengthened, reflecting an increased reciprocal transfer of nutrients and energy to terrestrial ecosystems
Summary
The habitats that form the interface between a stream and its adjacent terrestrial landscape are known as “riparian zones” [1] Streams and their riparian habitats are strongly connected hydrologically and ecologically and together provide valuable ecosystem services including intrinsic aesthetic values, recreational activities such as fishing, birdwatching and hiking and the supply of clean drinking water to human populations [2]. The significance of allochthonous matter is reflected in the diversity, taxonomic composition and feeding guilds (e.g., shredders and filter-feeders) comprising forested communities. Human activities, such as deforestation and landscape disturbances, that alter riparian vegetation composition can impact both terrestrial and stream ecosystems
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