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Measurements of leaf gas exchange were made in contrasting wooded ecosystems in West Africa. Measurements were made on 10 species: seven from humid rain forest in Cameroon and three from the semi-arid Sahelian zone in Niger. For each species, two models of photosynthesis were fitted: the first based on a rectangular hyperbolic response to photosynthetic photon flux density (Q), and the second the biochemical model of Farquhar et al. (1980). In both communities, the species studied could be divided into those characteristic of early and late successional stages, but photosynthetic parameters were not closely related to successional stage. The data identified significant relationships between V-cmax and leaf nutrient (N and P) content when expressed on an area basis. Variation in leaf mass per unit area correlated with canopy exposure and dominated the leaf nutrient signal. Statistical analysis suggested weakly that leaf gas exchange was more limited by P than N at the rain forest site.