Faculty Mentor

Geoffrey M. Henebry


The Grassland Destabilization Experiment (GDEX) is a landscape scale manipulative experiment initiated in 2004 in the Nebraska Sandhills to evaluate changes in surface properties following the abrupt loss of stabilizing vegetation. The GDEX features five treatments allocated among ten plots of 120 m in diameter (1.13 ha). The Aggressive Bare Sand protocol included chemical defoliation and subsequent shallow disking and raking in 2004 to devegetate the plot with periodic physical disturbance to maintain bare sand. The Long Term Disturbance (Press) protocol includes an initial chemical defoliation in May 2005 and seasonal spring reapplications, but no physical disturbance. Short Term Disturbance (Pulse) treatment had chemical defoliation initially in 2005 and again in 2008; thus, 2006, 2007, and 2009 are “recovery” years. There are two sets of controls: Grazed and Ungrazed. Eight plots (two replicates of each treatment) located contiguously within a fence are the focus of our investigation: Ungrazed Control, Pulse, Press, and Bare Sand. (We excluded the two Grazed Control plots that were located outside the fence away from the other treatments.) Erosion pin networks were established in each plot to track net (gain-loss) sand movement. Remote sensing data were acquired using the AISA Eagle imaging spectrometer in late June from 2006 through 2009. We tracked the spread of bare sand within and outside of the treatment plots by thresholding the upper range of values in the green (517 nm), red (666 nm), red edge (713 nm), and near infrared (856 nm) portions of the electromagnetic spectrum. The average reflectance across the full spectral range of the imagery (396-980 nm) at the erosion pin locations increased in the Press and Bare Sand treatments from 0.25 in 2006 to 0.30 in 2009; it decreased over the same period in Pulse treatments from 0.19 to 0.17 and in Ungrazed Controls from 0.17 to 0.14. Increases in the areal extent of bare sand in the neighborhood of the plots between 2006 and 2009 were an average of 5,742 m2 for Press treatments and 713 m2 for Bare Sand treatments. Four years elapsed before sustained sand mobilization occurred. We expect sand in the Bare Sand and Press treatments to continue to move as long as experimental treatments are maintained.



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