Understanding the economic value of avoided soil erosion in New Zealand is an important factor in policy decision making enabling the acknowledgement of the costs of erosion to the economy. This paper focuses on potential for afforestation to mitigate erosion risks on marginal agricultural hill country lands. Spatial economic modelling is undertaken to determine the net private and public benefit due to the avoided soil erosion from afforesting these areas. The study indicates that in some cases forestry is not viable and thus the public benefit from avoided erosion (and other ecosystem services) will not be forthcoming in these areas. Afforestation of these areas may therefore require positive incentives or improvements in forest and farm systems and technologies, depending on the relative weight of the public and private net benefits.