Inventory and Survey Methods for Nonindigenous Plant Species (PDF)

Chapter 7 • Adaptive Sampling DesignData CollectionData are collected using handheld computers with aglobal positioning system (GPS) unit attached. The handheldcomputers run ArcPad (ESRI Inc.) software, a GIS program.ArcPad menu screens are written specifically for the surveyproject and downloaded from a computer to the handheldcomputers. Several agencies and organizations now havetheir own screens for data entry, including the NationalPark Service, the USDA Forest Service, and The NatureConservancy (see Chapter 2).The user may record the NIS location (latitude/longitude,Universal Transverse Mercator [UTM], etc.) as either apolygon or point feature (see “Method,” above). Locationdata can be recorded (logged) while standing at the center ofthe patch. Location data for remote points can also be loggedby recording the crew member’s current GPS location andthen offsetting the location of the remote point by recordingthe distance, compass bearing, and inclination to the point.In addition to the NIS patch location, several data parametersare recorded, including the date, crew member, andNIS detected. The plant codes listed in the USDA PLANTSdatabase (http://plants.usda.gov/) are used to identify eachNIS. The radius of the patch is also recorded, along with anestimate of how the target NIS are distributed within theinfestation; i.e., whether coverage is uniform or scattered.Additional data can be taken but should be kept to only twoor three additional fields to prevent loss of survey efficiency.While these other data are being entered by the crew,the GPS is set with the tracklog on so that the whole areasampled by each crew is known. This log allows crews todelineate areas free of NIS as well as NIS-infested areas. Thisabsence information is as important as the presence information.Tracklogs can be set to record according to timeelapsed or distance traveled; distance traveled is preferred.All these data are saved within ArcPad as shapefiles on adata card that is later removed from the handheld computerand loaded onto a desktop computer running ArcView (ESRIInc.). Depending on the GPS used, data are either correctedusing Wide Area Augmentation System (WAAS) technologyor differentially corrected to improve accuracy. While moreexpensive GPS units do increase accuracy, often resourcesare limited and must be allocated to either equipment orpersonnel. When resources are limited, it is better to allocateresources to personnel rather than to expensive equipment.While accuracy may be reduced with less expensive equipment,surveying larger areas allows managers to make betterdecisions about allocation of resources dedicated to control.Errors of several meters should not jeopardize data collectionfrom an operational perspective. Relocating NIS witherrors of up to 15 m should not place the species outside thedetection distance.Equipment RequiredA handheld computer with a color screen visible indaylight and running Microsoft’s PDA operating system isrequired. The Compaq IPAQ has worked well, as have thenew Hewlett-Packard models with 640 by 480 pixel screens.We use a Nexia sleeve with the unit to provide two compactflash (CF) slots and an additional rechargeable battery. Anumber of CF slot GPS units are now available. Since modelschange rapidly, no specific models are listed here. A GPSunit that also allows attachment of an external antennashould be considered for use in steeper and forested terrain.A CF data card with a minimum capacity of 512 kilobytesshould be purchased to hold data. Clear adhesive screencovers are needed to protect the handheld computer screen.Cases that enclose the PDA and GPS but still allow datacollection can be purchased for additional protection.Data layers are downloaded onto the CF data card. Digitalorthophoto quads are used as a background data layer onthe handheld units to help crew members visually locatethemselves. Ownership boundaries are useful to include;roads and streams are visible on the orthophoto quads. Onthe desktop computer, ArcGIS ArcView (ESRI Inc.) is usedto store data in shapefiles. The ArcPad application buildersoftware is needed to build customized screens for datacollection on the handheld computers.Advantages and DisadvantagesAn important advantage of this survey technique is itsefficiency in mapping large areas, particularly when targetNIS are of limited distribution. By design, areas to surveyare limited to roads, trails, camping areas, livestock movementcorridors, and waterway systems, thus simplifyingsurvey planning. Targeting areas of human activity biasesthe survey to NIS that are primarily dispersed throughhuman activity. However, the perpendicular transect, used ifno NIS are found for 4 km, reduces the bias of the samplingtechnique. Utilizing such transects allows the survey crewto determine whether some NIS are found only in transects,which would suggest that stratification on a human disturbancefeatures only is inappropriate. If the NIS found in thetransect is a species of concern, then the survey techniquecan be adjusted.The hardware and software required by this method arerelatively inexpensive and easily used. Inexpensive handheldcomputers running ArcPad software allow flexibilityin data recorded through use of ArcPad custom screens.The data are saved as shapefiles so transfer to a desktopis easy. When budgets are tight, the handheld computerlinked to a GPS unit is considerably less expensive thanGPS with inbuilt computers and higher positional accuracy.58Inventory and Survey Methods for Nonindigenous Plant Species