Runoff and sediment yield relationships with soil aggregate stability for a state-and-transition model in southeastern Arizona

Soil erosion has been identified as the primary abiotic driver of site degradation on many semiarid rangelands. A key indicator of erosion potential that is being increasingly implemented in rangeland evaluations is soil aggregate stability (AS) as measured by a field soil slake test. However, there have been few studies that test if decreasing AS is an indication of increasing soil erosion. A rainfall simulator experiment was conducted in southeastern Arizona to measure runoff and erosion, aggregate stability, and cover attributes on three vegetation states of the state-and-transition model (STM) of the Loamy Upland ecological site (R041XC313AZ). The states included the reference state (RS), a site encroached by mesquite (MN), and a site invaded by Eragrostis lehmanniana (ML). Within the context of the STM, runoff was only different between very high and low cover states. Erosion and AS values differentiated among states, particularly between the RS and MN states. Relationships between runoff and erosion with canopy cover and interspace bare soil suggest that certain cover levels exist where runoff and erosion have the potential to increase. The results also indicated that for this ecological site, AS < 4 may represent an increased risk of erosion occurrence.