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We employed simple GIS methods primarily utilizing the South Dakota Farm Service Agency’s Common Land Unit (CLU) data layers from 2013 and the 2012 United States Department of Agriculture (USDA) National Agriculture Imagery Program (NAIP) county mosaic aerial imagery to evaluate 7,347,812 acres of land in northwestern South Dakota. The analysis area includes: Harding, Perkins, and Butte counties along with portions of Lawrence and Meade counties outside of the Black Hills Core Highlands and Plateau Ecoregions.
We utilized the FSA CLU data layer queried to show current and former cropland to identify and remove any areas with cropping history regardless of current land use. We analyzed the remaining land in approximately one mi2 sections to identify and remove additional historic or current land disturbances. The remaining land tracts were categorized as potentially ‘undisturbed grassland’ or ‘undisturbed woodland’ by simple reason of deduction. Finally, we removed all known water bodies larger than 40 acres as defined by the South Dakota Department of Game, Fish, and Parks’ (SDGFP) Statewide Water Bodies layer to gain a more accurate interpretation of the remaining undisturbed grassland/wetland complex.
Overall, 5,743,137 acres (78.2%) of the approximately 7.3 million-acre analysis area was designated as potentially undisturbed by our initial analysis (Figure 1). However, a portion of these undisturbed acres have certain indicators suggesting historical disturbance, thus 17,263 locations were flagged as potential ‘go-back’ areas (see updated Methods section). In addition to go-back areas, we also identified over 300 locations with indicators of some type of native rangeland manipulation other than historic cropping.
Because of limitations evaluating historic land patterns with NAIP imagery, it was not possible to accurately calculate actual area estimates for these flagged locations. However, we were able to perform an initial area analysis of go-back sites using polygons in portions of Harding and northern Perkins Counties which suggests the combined impact of go-back fields and rangeland manipulations may impact about 10% of the undisturbed land layer. Therefore, we speculate the actual undisturbed (potentially native) land area for this region may be reduced from the current 78.3% down to roughly 68% if we can refine our methodologies to more accurately reflect these disturbances in the future. We anticipate future LiDAR analysis will aid in improving such accuracy.
To provide the reader with a better understanding of the distribution of these flagged disturbances, we analyzed the number of legal sections of land (as defined by the 2000 Public Land Survey) that had at least one indicator of disturbance against the total number of legal sections in the analysis area. We found that 7,558 out of 11,580 (65.3%) legal sections had at least one indication of disturbance within the section (either a go-back site or rangeland manipulation site within the undisturbed land layer).
Of the approximate 7.2-million-acre total analysis area, 1.4 million acres (19%) were deemed to have a cropping history according to the FSA CLU data. 193,570 acres (2.6%) were found to have some type of land disturbance not indicated by a CLU crop code. Totaling 1.59 million acres (21.7%) of all land with some type of proven disturbance history. Leaving roughly 5.7 million acres deemed undisturbed.
Within the approximate 7.2-million-acre total evaluation area, 12,315 acres (0.2%) were found to have some sort of permanent protection from conversion (some of these acres have a disturbance history). Only 10,835 acres of the approximately 5.7 million acres of undisturbed land (0.2%) had some level of permanent conservation protection status. The 10,835 acres of potentially undisturbed land that is officially protected from future conversion represents only 0.1% of the analysis area for the five northwestern South Dakota counties.
Within northwestern South Dakota we identified 298 oil wells, drill sites, and associated facilities/developments. These sites are primarily located in the Sagebursh Steppe Ecoregion of Harding County. Of the sites identified, 262 (87.9%) were located adjacent to undisturbed areas (within 250 feet, see Methods section).
Environmental Sciences | Life Sciences | Physical and Environmental Geography | Remote Sensing
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