While slash-and burn farmers convert forest to agriculture, they also regenerate significant areas of secondaryfallow forests on their farms. Under what conditions does secondary forest cover persist on slash-and-burn farms?Survey data from Pará, Brazil show that secondary forests occupy 20% of farm area even after a century ofsettlement. In addition to restoring soil fertility, secondary forests contribute over 20% of farmersʼ income throughproducts such as charcoal, fruit, game animals and firewood for on-farm processing. Econometric analysis showsthat slow rates of population growth and increases in agricultural incomes through on-farm processing of agricultural products enable farmers to maintain long fallows and result in diversified systems compatible with secondary forest cover in the study area. On the other hand, declining agricultural productivity, subsidized credit,declines in the growth rate of secondary forests and policies favoring speculative land acquisition threaten secondary forest persistence. In older settlement areas, secondary forests are often the only forest resource availableto the rural poor. Fallow areas should therefore be managed not only for agricultural productivity, but also forconserving forest resources.