Development of a plant-soil-water (ecohydrology) model to aid in predictions of rangeland ecosystem goods and services

About the Presentation

Systems analysis has aided in analyzing and predicting the impacts of various management strategies to many rangeland issues, including grazing effect on annual net primary production, animal health (e.g., livestock body condition scores), ranch profitability (i.e., from alternative stocking rates), or wildlife populations (e.g., interaction between climate and harvest strategies). Based on previously published models, evidence suggests that rangeland models could be enhanced through the incorporation of ecohydrology concepts, particularly as it relates to forage supply and water balance on rangelands. Previous rangeland models have relied on: a) empirical relationships of precipitation and plant production; and b) coupling these estimates to assumed coefficients about range condition and previous rainfall trends; in order to c) model forage supply usable for grazing or wildlife through changes in range condition, irrespective of changes in plant community composition. On the other hand, ecohydrology models have focused on the importance of soil texture and the basic water balance equations to model infiltration, excess runoff, and changes in plant community composition through changes in evapotranspiration, which is partly driven by available soil moisture. By combining approaches, rangeland models could account not only for grazing impacts on production and profitability but also the impacts on site-specific hydrologic function, which should prove useful given uncertain climate changes and increasing awareness of ecosystem goods and services. In this poster, I present a simple plant-soil-water model created in Stellaâ„¢ (iSeeSystems, Lebanon, NH) that illustrates how ecohydrology concepts could be incorporated into new or existing rangeland models. The model is calibrated to observed data from four locations of diverse soil properties and climate characteristics in Texas (Seymour, Palestine, San Marcos, and Edinburg; TAMU North America Soil Moisture Database). Early diagnostic and sensitivity tests will be presented. Lastly, some model limitations are described along with directions of future work, including feedback loop dominance analysis.

Estimating Erosion, Water Quantity and Quality Changes in Response to South Dakota Grassland Conversion using System Dynamics

About the Presentation

South Dakota is a mosaic of grasslands, wetlands, and cropland. A continued shift from grassland to cropland has occurred over the past 10 years and is expected to continue for the next 50 years. The rate of future conversion may vary greatly depending on economics, policy, and demographic factors. In any case, the land conversion will influence cumulative erosion from arable soils which could potentially impact stream and river hydrology and water quality. Quantifying future changes for these three externalities is important to understand the possible consequences of grassland conversion. This presentation will show forecasted results for rill and sheet erosion, water quality and quantity for a subset of my study area within the Big Sioux River (BSR) water catchment under various grassland conversion scenarios. A System Dynamics approach will address the dynamic complexity of this system by capturing its structure and behavior and revealing key leverage points that influence change for these environmental externalities. It also provides a robust method to generate estimates for water catchments with fewer data. Annual grassland conversion has been captured using a recently developed thematic map of the contiguous United States (1947-2062; USGS 2014). Spatial land cover, soils, and climate data have been delineated by hydrologic unit codes 10 (HUCs). The subset HUC-10, Skunk Creek, model provides forecast future annual erosion, water quantity and quality under different potential future grassland conversion rates over the next 50 years. This initial model will then be locally calibrated for the remaining study area in the BSR and the other water catchments to provide sub-catchment and whole catchment estimates, giving insight for future landscape scale externalities of grassland conversion in South Dakota