Canada's forests provide a range of ecosystem services that are vital to human health such as purifying water, stabilizing soil and nutrient cycles, and providing habitat for wildlife rich in biological diversity. The potential impacts of nitrogen and sulphur deposition on ecosystem services provided by Canadian forests were assessed using the concept of critical loads, a well-established scientific effects-based approach for assessing the environmental consequences of air pollution at large regional or national scales. Exceedance of critical load, that is, deposition in excess of critical load, suggests that provisioning, regulating and supporting ecosystem services of Canadian forests (e.g. water quality, soil quality and plant species diversity) are negatively impacted by nitrogen and sulphur deposition. Under modelled 2006 total deposition, widespread exceedance was predicted for critical limits associated with long-term soil quality and plant species diversity. Given both the positive and negative impacts of atmospheric deposition, it is important to employ holistic approaches to assess how future emission reduction policies will affect the quality and quantity of ecosystem services.