Global and local ecosystem change resulting in diversity loss has motivated efforts to understand relationships between species diversity and ecosystem services. However, it is unclear how such a general understanding can inform policies for the management of ecosystem services in production systems, because these systems are primarily used for food or fibre, and are rarely managed for the conservation of species diversity. Here, using data from a nationwide forest inventory covering an area of 230,000 km2, we show that relative abundances of commercial tree species in mixed stands strongly influence the potential to provide ecosystem services. The mixes provided higher levels of ecosystem services compared to respective plant monocultures (overyielding or transgressive overyielding) in 35% of the investigated cases, and lower (underyielding) in 9% of the cases. We further show that relative abundances, not just species richness per se, of specific tree-species mixtures affect the potential of forests to provide multiple ecosystem services, which is crucial information for policy and sustainable forest management.