Evaluating the ecological effectiveness of landscape-level collaborative conservation: A case study targeting wild bees

Collaborative multi-actor conservation has been heralded as an effective way to address historical biodiversity loss because it makes landscape-level multi-habitat management strategies possible. However, its ecological effectiveness is not well understood. We examine a multi-actor approach in which 11 organisations collaborated to enhance wild bees in a 30 km 2 landscape in the south of the Netherlands. Using a novel study design for landscape-level conservation initiatives, we compared six-year trends in wild bee abundance and species richness and flower cover and species richness in 47 sites with bee-friendly management aimed at increasing the spatio-temporal availability of flowers in five habitats (extensive pastures, road verges, field margins, hedgerows, water retention sites) with trends in similar numbers of conventionally managed controls inside and outside the landscape. Overall, wild bee abundance and species richness increased in sites with bee-friendly management relative to controls, though effectiveness varied by habitat. Across all sites, bee-friendly management resulted in significantly more positive trends in flower cover than in control sites, yet trends in managed sites were stable rather than increasing and flower cover declined by approximately 46 % in control sites. The implementation success of bee-friendly management varied by habitat type and year, and was a key factor underlying the ecological effectiveness of said management. Our results suggest that coordinated collaborative approaches across complementary habitats can produce conservation benefits, but that success depends on effective communication with and consistent participation of actors, guidance by a coordinator, and continuous monitoring of management implementation and ecological outcomes.