Inventory and Survey Methods for Nonindigenous Plant Species (PDF)

Tiered Sampling Method: Nevada’s ProtocolChapter 5Robert E. Wilson, Ted Angle, and Maria RyanIntroductionNevada is a region primarily of large landscapes withfew towns or people. Detecting nonindigenous plantspecies (NIS) in these vast landscapes is problematic.Although there are places where NIS may predictablybe found (e.g., roadways, waterways, disturbed areas),it is important that NIS be detected in more nonpredictableareas (e.g., forests, grasslands) as well. The tieredsampling method provides an approach to locating andrecording infestations that has proven effective andefficient. The method employs three tiers to enableland managers to locate NIS in both predictable andnonpredictable situations with a reasonable degree ofaccuracy and reliability.ObjectivesThe primary goal of the tiered sampling method is todetect and map the location, density, and spatial extent ofspecific established populations of nonindigenous plant specieswithin the area of interest. The tiered sampling methodis being used to map most of the state of Nevada’s noxiousweed species, and this is the example presented throughoutthis chapter.The term survey is defined here as an investigation of anarea using a sampling method to obtain an estimate of theNIS populations. Not every square yard is observed in thesurvey sampling process. Information gathered through thesampling is extrapolated to unsurveyed areas. Elsewhere inthis chapter, the term inventory is used to reflect an intensiveviewing of an area in order to gain an accurate understandingof the NIS population over the entire area. The methoddescribed in Tier I is considered in this chapter to be aninventory, while Tier II and III methods are considered tobe surveys. Thus, the inventory/survey terms are used inaccordance with the definitions in Chapter 1.Managers need to know which NIS are problems, andwhere they are, before they plan strategies of control or containment,and to avoid actions which would make the NISproblem more severe. The U.S. Bureau of Land ManagementEly Field Office Resource Management Plan/EnvironmentalImpact Statement for the Ely District (available from theEly Field Office, 775-289-1880) provides an example of theneed for knowledge about noxious weed populations beforemanagement activities are implemented. However, it is obviouslyimpossible to devote adequate resources to inventoryall noxious weed populations, let alone all NIS populations,over very large landscapes. In Nevada noxious weeds are thetarget of the sampling protocol. The sampling protocol usesa tiered approach to prioritize inventory/survey locationsand to ensure with some degree of accuracy that most ofthe target species populations will be located. Based on thepremise that disturbed areas are the most likely places forthe target populations to occur or become established, TierI inventories are directed toward disturbed or wet areas(e.g., along transportation systems, and around waterwaysor water bodies). The second tier surveys occur in areaswith limited disturbance that are presumably less probablesites for NIS invasion. Thus, Tier II surveys are performedto locate target species infestations that might have beeninadvertently introduced by other means (e.g., livestock,wildlife, humans) into remote and/or undisturbed areas. Thethird tier is a random check to validate the reliability of theinventory and survey completed in the first and second tiers.Essentially, Tier I is an inventory because all disturbed areasare sampled, while Tiers II and III are surveys because theyare subsamples of the whole area. Regardless of the tier level,when a target area is defined the whole area is sampled.This multitiered approach is designed to ensure a highlevel of accuracy, reliability, and repeatability across thelandscape. In Nevada this approach provides greater than90% confidence that all noxious weed infestations have beenfound. The data should be added to a central geographicinformation system (GIS). Once target NIS populations havebeen located, control or management efforts can begin.Information on these efforts should also be added to the GIS,and some of the populations monitored. Such field collectionof data and record keeping allow for evaluation of the controland management effectiveness.Using the tiered approach means that the inventory/surveycan be tailored to meet a variety of different land use andinventory/survey objectives, and can be adjusted accordingto constraints such as funding, area, and/or desired accuracy,as described in Chapter 1. For example, managers maybe interested in finding as many NIS patches as possibleso they can be eradicated from an area, or they may need ageneral assessment of NIS present in a large area. The followingsection on planning includes a series of questions asurveyor using the tiered method will need to address at thestart of the inventory/survey so that the sampling protocolcan be adjusted accordingly. If the method is modified; i.e.,if one or more tiers are removed from the protocol, thenthe confidence level will decline significantly. Managementof NIS populations is separate from the inventory/surveymethodology.MethodPlanningThe inventory/survey protocol presented was developedin east-central Nevada in the Tri-County Program and has42Inventory and Survey Methods for Nonindigenous Plant Species