Application of soil physical models to predict soil deposition effects on plant establishment

Background/Question/Methods

Soil erosion and deposition often result in significant soil profile modifications, including soil surface texture and structure changes. These properties affect water infiltration and available water holding capacity, both of which affect plant water availability. Because plants are especially sensitive to desiccation during establishment, near-surface changes in these properties can have significant effects on plant community dynamics. The objective of this study was to quantify the effects of soil erosion and deposition on plant establishment, and to explore the patterns of shrub encroachment associated with soil deposition. A field study and a series of modeling exercises were completed at the Jornada Experimental Range in association with the Jornada LTER. The Jornada is located in the northern Chihuahuan Desert in south-central New Mexico, and receives approximately 245mm of precipitation, the majority of which arrives during the summer growing season. The field study included repeat air photo analysis, detailed mapping of plant cover, composition and spatial structure, field soil interpretation, and characterization of contemporary soil redistribution based on cesium analyses.

Results/Conclusions

Sand deposition on a loam-textured soil was predicted to reduce near-surface plant-available water holding capacity from 13% to 9% while increasing infiltration capacity from 15 to 126 mm per hour. Model runs showed that the effects of sand deposition on grass establishment similarly depended on the amount of sand added and soil surface texture. Sand deposition tended to have the greatest positive effect on fine-textured soils. By reducing evaporative losses, sand deposition can increase the amount of time that water is available to seedlings.  Field studies of areas where sand deposition has been occurring during the past several decades showed highly variable rates of mesquite encroachment into grasslands, and that grassland loss occurred even in areas where the hydrologic conditions for grass establishment were improving. The results suggest that additional factors must be considered in developing predictive models of the effects of soil deposition in arid and semi-arid ecosystems.