Umeå University's logo

Decades of forest management in the boreal biome have involved digging drainage ditches and modifying streams to increase timber production, altering terrestrial ecosystems and expanding stream networks. Modified waterways and drainage ditches represent widespread novel aquatic and riparian ecosystems, with little known about their biodiversity. With approximately 68% of small waterways in Sweden human-made or modified, improved knowledge is needed to inform effective management of biodiversity of these often-disregarded habitats. Currently, ditches and modified waterways may undergo ditch network maintenance, involving the removal of debris and vegetation, with less emphasis placed on protecting them with vegetated buffers compared to natural waterways. In this study, we surveyed riparian vegetation across soil types (till and peat) along a drainage size gradient (0.5–60 ha) in a northern boreal catchment, assessing the riparian vegetation among ditches, modified waterways, and “natural” streams. We found that the vegetation in this catchment did not differ significantly between modified waterways and streams on till soils, highlighting an important role for modified waterways in maintaining riparian vegetation diversity. Till ditches exhibited similar community composition, although significantly lower diversity, compared to modified waterways and streams on till. By comparison, peat ditches harbored less vegetation diversity and exhibited lower species turnover and different community composition, driven by variation in soil conditions and catchment size. Our study demonstrates that plant species diversity and richness increase with catchment area along a ditch to stream gradient, highlighting a pattern well established in natural systems but underexplored in the context of artificial and modified waterways. To enhance vegetation diversity in boreal landscapes, conservation planning should include modified waterways on till soils. Management recommendations include avoiding ditch maintenance in self-eroding till systems and prioritizing the rewetting of sites with peat ditches and small catchments. Rather than a uniform restoration approach, our results advocate for catchment-scale planning and tailored ecological endpoints to maximize biodiversity and ecosystem resilience.