The consequences of considering ecosystem services (ES) in conservation assessment are still widely debated. The degree of success depends on the extent to which biodiversity and ES can be secured under joint conservation actions. Unlike biodiversity, ES conservation is inseparably linked to human beneficiaries. Reconciling biodiversity with ES and conservation can be particularly challenging in sparsely populated areas. This study, in a sparsely-populated region of eastern Canada, focused on freshwater wetland biodiversity and ten ES provided by wetlands. Within a given maximal total area, the results showed that planning for biodiversity underrepresented local flow ES supply by 57% and demand by 61% in conservation networks. Planning for ES alone underrepresented wetland biodiversity surrogates by an average of 34%. Considering both biodiversity and ES simultaneously, all of the biodiversity and ES targets were achieved with only a 6% mean increase in area. Achieving all conservation targets starting from a network that was primarily built for either ES or biodiversity features alone was two to five times less efficient than considering both ES and biodiversity simultaneously in conservation assessment. A better framework is required to translate these spatial synergies into effective joint conservation actions.