Inventory and Survey Methods for Nonindigenous Plant Species (PDF)

Chapter 7 • Adaptive Sampling DesignSecond patch found}}ID distance onlyThird patch found}ID distanceplus 2 m100 m maximum distance from original patch100 mFirst patch found}Identification distance plus 2 mStarting Original point on patch patch edge(on random azimuth from center)GPS locationGPS location in center of patchOriginal patcht Figure 1. Hypothetical map showingNIS patches (solid light blue areas), theirboundaries (solid lines), and the adaptivesampling walking paths (dashed lines)used for finding new patches of the samespecies. In this example a detectiondistance of 2 m was used with a maximumdistance (outer boundary) from theoriginal patch of 100 m.perpendicular to the trail for 400 m(Figure 2) to check that the chosenstratification variable (in this case trails)was valid. If target NIS are not foundalong the perpendicular transects, thenthe crew returns to the trail or area ofinterest and the survey continues.Detection DistanceThe distance between crew memberswhen they are sampling an area iscalibrated in the field with known locationsof NIS to ensure that the sampledarea is covered adequately. The crewmembers walk away from a targetedNIS population until they no longer feelconfident about visual identificationof the plant. The longest identificationdistance they feel confident with islabeled the detection distance. Thedetection distance is often no less than10 m. Twice the detection distance isused to establish the distance betweencrew members. In addition to definingthe detection distance, the crewmember is creating a mental image(a search image) of the target NIS inthat environment. Multiple NIS canbe targeted with this method, but it isbest suited to mapping of six or fewerspecies. Experience shows that surveycrew members can retain at least 10to 12 search images for an extendedperiod.▲ Figure 2. A section of the Lewis and Clark Trail surveyed in 2003 using the adaptive sampling method. The area along thetrail and the four transects are presented in brown, and NIS locations are presented as red circles. The NIS infestation awayfrom the trail (upper arrow) was found using the adaptive concentric circle approach as a result of originally locating the NISpatch on the trail’s edge (lower arrow). The maximum distance (i.e., outer boundary) to be walked from the original patch was800 m; the patch away from the trail (upper arrow) was within 800 m.Inventory and Survey Methods for Nonindigenous Plant Species57