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Few empirical data exist to examine the influence of regional scale environmental gradients on productivity patterns of plant species. In this paper we analyzed the productivity of several dominant grass species along two climatic gradients, mean annual precipitation (MAP) and mean annual temperature (MAT), in the Great Plains of the United States. We used climatic data from 296 weather stations, species production data from Natural Resource Conservation Service rangeland surveys and a geographic information system to spatially integrate the data.

Both MAP and MAT were significantly related to annual above-ground net primary production (ANPP). MAP explained 54 % to 89 % of the variation in ANPP of two C-4 short-grasses, Bouteloua gracilis and Buchloe dactyloides, and two C-4 tall-grasses, Andropogon gerardii and Schizachyrium scoparium (= Andropogon scoparius). MAT explained 19 % to 41 % of the variation in ANPP of two C-4 grasses, B. gracilis and B. dactyloides, and 41 % to 66 % of the variation in ANPP of two C-3 grasses, Agropyron smithii and Stipa comata. ANPP patterns for species along both gradients were described by either linear, negative exponential, logistic, normal or skewed curves. Patterns of absolute ANPP (g/m(2)) for species differed from those of relative ANPP (%) along the MAP gradient. Responses were similar for species with common functional characteristics (e.g. short-grasses, tall-grasses, C-3, C-4).

Our empirical results support asymmetric responses of species to environmental gradients. Results demonstrate the importance of species attributes, type of environmental gradient and measure of species importance (relative or absolute productivity) in evaluating ecological response patterns.