Turning old foes into new allies – harnessing drainage canals for biodiversity conservation in a desiccated European lowland region

1. Drainage canals are widespread components of agricultural landscapes. Although canals have greatly contributed to biodiversity loss by desiccating wetlands, they have recently attracted conservation attention due to their potential to function as refugia for native species in intensively managed landscapes. However, their conservation role in complex landscapes composed of agricultural fields and desiccated but otherwise untransformed, semi-natural habitats, on which canals still pose a heavy burden, is unknown. Improved understanding of drainage canals and related biodiversity in these landscapes could help unlock their potential and support synergistic land management for nature conservation and water resource management.

2. We applied a multitaxon approach, including plants, butterflies, true bugs, spiders and birds, to (1) assess the conservation value of drainage canals with temporary water cover in a heavily drained European lowland region, (2) to test landscape-level and local canal parameters for aiding prioritization among canals, and (3) to propose a reconciliation-based management framework that suits the interest of all stakeholders.

3. We found that drainage canals and their banks concentrate more species across most taxa than semi-natural, mostly grassland habitats, possibly due to micro-environmental heterogeneity and the absence of low-intensity annual management compared to grasslands. Canals traversing semi-natural grasslands concentrate particularly high numbers of native species, but agricultural canals also support remarkable species richness. However, agricultural canals are important dispersal corridors for non-native invasive plants, which may negatively affect native biodiversity. Canal size has little effect on biodiversity but habitat stress is an important determinant. The higher the stress (due to sandiness and salinity), the higher is the added value of canals to landscape-wide biodiversity.

Synthesis and applications. We show that drainage canals can harbour high biodiversity and should therefore be recognized as important novel ecosystems with high conservation value, even when cutting through semi-natural grassland habitats. Canals have previously been considered detrimental to nature conservation due to their association with loss of wetlands. However, by reducing water loss with reversible obstructions, controlling invasive species and applying specific conservation measures, they may be turned into conservation allies without compromising long-term interests of water management and agricultural land use.