Submitted to: Journal of Vegetation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/1998
Publication Date: N/A
Interpretive Summary: Soil texture is hypothesized to have an important effect on aboveground production of plants in rangelands. In dry areas, fine-textured soils high in silt or clay content are predicted to have lower plant production than coarse-textured soils high in sand due to physical properties of the soils; the reverse is predicted in humid areas. In our study, we tested this hypothesis by collecting plant production at 7 fine- and 7 coarse-textured sites along a climatic gradient from eastern Colorado to eastern Nebraska. We found that plant production across this Central Grasslands region increased with increasing precipitation and was more strongly determined by current year's precipitation than by soil texture or temperature. Although soil texture did not affect total plant production, it did affect the amount of grass, forb, and shrub production across the gradient. Forb and shrub production was highest on the coarse-textured soils. Our results are important to the management of these grasslands since they indicate that production of forbs and shrubs is determined by soil texture, yet total production on different soils may be similar.
Technical Abstract: The inverse texture hypothesis predicts that in arid and semiarid regions plant communities on coarse-textured soils should have higher above-ground net primary productivity (ANPP) than those on fine-textured soils; the reverse should occur in more humid regions. Our first objective was to test predictions from the inverse-texture hypothesis using 2 years of ANPP data for 7 coarse- and 7 fine-textured natural grassland sites located along a precipitation gradient through the Central Grassland region from eastern Colorado to eastern Nebraska. Using these same sites, our second objective was 1) to evaluate changes in vegetation structure, specifically basal cover and functional type composition, on coarse-and fine-textured soils across a precipitation gradient, and 2) to evaluate how these changes may affect ANPP. In 1993 and 1994, ANPP increased significantly with increased August-July precipitation for coarse- and fine-textured sites. Neither the slope nor the intercept of the regression line relating ANPP and precipitation varied with soil texture. Across the gradient, graminoids made up the largest proportion of total ANPP for both textures and years. Forbs and shrubs made up a larger proportion of total ANPP on coarse- compared to fine-textured sites. Shrubs contributed more to ANPP at the driest (shortgrass steppe) sites compared to the wetter sites, whereas the ANPP of forbs increased with increasing precipitation. Our results revealed that ANPP across a regional precipitation gradient through the Central Grasslands was more strongly determined by current year's precipitation than by any other factor we considered. Soil texture may play a larger role in determining vegetation structure than in determining total ANPP.