Soil texture and precipitation seasonality influence plant community structure in North American temperate shrub steppe

Abstract

In drylands, the coexistence of grasses and woody plants has been attributed to soil-water resource partitioning. Soil texture and precipitation seasonality can influence the amount and distribution of water in the soil, and their interaction may play an important role in determining the relative importance of grasses and woody plants. We investigated the influence of this interaction on plant functional types across a broad range of precipitation regimes and soil textures in western North America by analyzing plant-cover data collected at 2,084 plots that included the widespread shrub big sagebrush (Artemisia tridentata Nutt.). We characterized how the significance of the inverse-texture effect varies across soil conditions by quantifying relationships between precipitation and foliar cover on finer- vs. coarser-textured soils across a range of potential texture divisions represented by sand content. We found evidence of the inverse-texture effect for every plant functional type (except for cheatgrass) that we examined with at least one component of precipitation (annual, warm, or cold season), and provide the first evidence for this effect in locations with cold-season-dominated precipitation regimes. The texture and precipitation combinations that exhibited the inverse-texture effect varied with plant functional type, presumably because of effects of soil texture on water availability at different soil depths with season. Furthermore, we found an inverse-texture effect that was remarkably similar for shrub cover with cold-season precipitation and grass cover with warm-season precipitation. These results provide new insight into how the inverse-texture effect interacts with precipitation seasonality to influence plant functional type composition in drylands, and further suggest that quantifying the soil-texture division at which the inverse-texture effect is relevant under a given set of environmental conditions may provide support for the effect across dryland plant communities.

Keywords: Artemisia tridentata; Walter's two-layer hypothesis; dryland vegetation; inverse-texture effect; resource partitioning; soil moisture.