Basin‐scale variables drive macroinvertebrate biomass in low‐order streams across different mountain ecoregions.

Aim: Biomass is an important descriptor of macroinvertebrate communities, providing insights into stream productivity and ecosystem functioning. Nevertheless, the drivers of biomass are still poorly assessed, especially in multiscale studies. Here, we aimed at filling this gap by assessing the relationship between environmental variables measured at patch, reach and basin scale and macroinvertebrate biomass, as well as the transferability of such relationships across different mountain regions. Location: Maritime‐Cottian Alps and the Tuscan‐Emilian Apennine (Northern Italy). Taxa: Freshwater macroinvertebrates. Methods: Patch‐, reach‐ and basin‐scale variables, either measured in the field or computed with kriging techniques, were summarised with sparse principal component axes and later used in mixed modelling and variance partitioning to assess the relative effect of environmental variables on macroinvertebrate biomass. An independent model was run for each region, and results were compared to assess the transferability of drivers. Results: Basin‐scale variables explained most of the biomass variability in both regions, supporting the transferability of results. More specifically, mean cumulated daily precipitation was the main driver of macroinvertebrate biomass. Patch‐ and reach‐scale variables also significantly affected macroinvertebrate biomass, but their relative role varied depending on the region considered, without any clear pattern. Main Conclusions: Overall, we highlighted a dominance of basin‐scale drivers—and specifically of the mean cumulated precipitation—and a consistency of results across different mountain regions. This implies that climatic variables regulate energy fluxes to higher trophic levels and subsidies to both downstream river sections and terrestrial ecosystems. These findings offer insights into ecosystem‐level vulnerability to climate change. [ABSTRACT FROM AUTHOR]