Spatio-temporal changes in Quercus gambelii Nutt. foliar chemistry were measured along an elevation gradient. The carbon-nutrient balance hypothesis predicts nutrient use and carbon allocation is determined through balancing effects of competition and herbivory. Accordingly, when nutrients are in ample supply, it is predicted competition should favor carbon use primarily in growth. Conversely, within nutrient stressed environments, change in carbohydrate status is expected to increase carbon amounts allocated for defense. Competition pressure varies with edaphic and ambient quality. Changes in topography represent sharp local gradients of environmental heterogeneity that can affect plant and insect populations and communities. Foliar carbon/nitrogen ratios were measured across several elevations on Mount Withington in the Cibola National Forest of west-central New Mexico U.S.A.. Preliminary analyses indicate variation in leaf chemistry with elevation. This variation produces a cascade of bottom-up effects through which Q. gambelii foliar chemistry may influence preference-performance in moths of the genus Phyllonorycter (Lepidoptera: Gracilariidae), a Q. gambelii associated leaf-mining herbivore. Larval performance is currently being investigated.

Key words: carbon nutrient balance hypothesis, cascade, chemistry, Quercus, trophic