More than just a margin: Local and landscape‐scale factors regulating the effects of riparian forest buffers on stream‐riparian ecosystems in urban and agricultural landscapes

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Abstract Riparian forest buffers are a potentially potent nature‐based solution for mitigating environmental degradation and improving biodiversity and ecosystem functioning in stream‐riparian networks. However, uncertainties about how buffer size, spatial configuration and land‐use intensity shape outcomes and trade‐offs hinder management applications. We conducted coordinated field surveys and modelling across four European countries to evaluate how riparian forest properties influence stream‐riparian environments, biodiversity, ecosystem processes and macroinvertebrate functional traits along agricultural and urban land‐use gradients. Riparian forest buffers had strong effects on habitats, increasing shading and coarse woody debris. Sediment deposition was halved in buffered stream reaches, and longer buffers lowered thermal maxima in stream and riparian habitats by 13%–17%. Buffers further reduced effects of increasing agricultural land use on soluble reactive phosphate concentrations, although this response was highly variable. These environmental changes were associated with multiple effects on biodiversity and ecosystem function. Buffer presence and/or increasing length were associated with 30%–167% increases in microbial detritus decomposition, a 44% increase in riparian ground beetle diversity, and 18%–77% increases in stream macroinvertebrate diversity and the EPT biotic index, and macroinvertebrate leaf shredding and algal grazing traits. In contrast, algal biomass accrual and web‐building spider diversity declined by 33% and 36%, respectively, in buffered reaches. As land‐use intensified, riparian forest buffers helped maintain macroinvertebrate functional diversity and shredding, predation, and filtration traits, and saturated fatty acid content in terrestrial predators. In contrast, macroinvertebrate particle‐gathering traits declined. The spatial configuration of riparian forest influenced stream ecosystems at local scales: dissolved phosphorus and diatom species richness declined as spatial proximity among upstream riparian forest blocks decreased, while a diatom‐based biomonitoring index increased. Synthesis and applications . Riparian forest buffers support biodiversity, ecosystem functioning and food webs in human‐modified landscapes, and dampen land‐use and climate stressors (sediments, nutrients, thermal maxima), motivating their wider use in management. These outcomes were regulated by the presence or size of mostly small, mature buffers and sometimes by proximity among riparian forest blocks upstream, indicating that even modest investments in expanding existing buffer networks are likely to deliver cumulative ecological benefits.

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