Tracked vehicle impacts to vegetation structure and soil erodibility

There has been increasing concern that training on military lands results i n excessive soil erosion, ecosystem degradation, and loss of sustainable tr aining resources. Vegetation structure has been shown to play a role in soi l surface stabilization by reducing shear stress caused by wind force. A st udy at the Idaho Army National Guard training facility at Orchard Training Area (OTA), Ida. assessed the effect of simulated M1A2 Abrams battletank ma neuvers on grassland plant canopies and soil erodibility. The point-interce pt method was used to estimate vertical vegetation structure before and aft er tracking. A portable wind tunnel was used to measure threshold wind spee ds (TWS) associated with different numbers of tank passes and soil mass rem oved by wind. Results indicated that significant damage occurred to vertica l vegetation structure as the number of passes increased. Threshold wind sp eed, an indicator of soil surface stability, significantly decreased with t racking and eroded soil mass significantly increased. Positive correlations existed between vegetation parameters and threshold wind speed. Soil loss was negatively correlated with vegetation parameters. Results indicated tha t the decrease of vertical vegetation structure led to a decrease in thresh old wind speed. This decrease in threshold wind speed was the result of red uced soil surface protection by vegetation. Decreased surface protection al so resulted in increased soil loss. Results from this work confirmed that v egetation plays a major role in reducing shear stress on the soil surface. Predictions for soil loss at Orchard Training Area resulting from the numbe r of M1A2 passes are made using linear models. A critical tracking threshol d of 4 passes was estimated based upon model output and average local wind speeds for Orchard Training Area.