Effect of perturbing the geographic coordinates of forest inventory plots on hotspot cluster detection

KaDonna Randolph


The USDA Forest Service Forest Inventory and Analysis (FIA) program makes and keeps current an inventory of all forest land in the United States. Data from this ongoing inventory are available to the public, though FIA is restricted from releasing exact plot locations by the 2000 Interior and Related Agencies Appropriations Act (H.R. 3423). To comply with this policy while at the same time offering its data to the public, FIA makes approximate plot locations available through a process known as perturbing and swapping. This process has little to no effect on some research questions and a considerable effect on others. In this study, using the perturbed and swapped, i.e., the publicly available plot locations, was shown to affect the location, size, and composition of clusters of standing dead trees in the eastern United States as detected by the free spatial scanning software program SaTScanTM. When employing SaTScan with publicly available FIA plot coordinates as compared to using the confidential FIA plot coordinates, users risk identifying a cluster that does not exist (false positive) or failing to identify a cluster that does exist (false negative), or both.


FIA data; point pattern analysis; SaTScan; spatial scan statistic

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