Two hypotheses of nutrient cycling during succession are considered. First, Odum's hypothesis that nutrient cycles “tighten” as succession proceeds, i.e. cycling within the system increases. Second, Vitousek and Reiners' hypothesis that the ratio of output to input will decrease at first as net ecosystem production (NEP) increases and then return to unity as NEP approaches zero. The two hypotheses are compatible and this is demonstrated using a simple model of nutrient cycling during succession. This suggests two independent processes involved in nutrient conservation, namely, nutrient accumulation and nutrient cycling.