Inventory and Survey Methods for Nonindigenous Plant Species (PDF)

Getting Started: Fundamentals ofNonindigenous Plant Species Inventory/SurveyChapter 1Monica L. Pokorny, Steven A. Dewey, and Steven R. RadosevichIntroductionManagement programs for nonindigenous species(NIS) exist to help achieve the overall land use goalsfor an area. Without clearly defined land use goalsand an NIS management program aimed at achievingthose goals, the reason for an NIS management plancan be unclear and unquantifiable. Defining land usegoals and NIS management objectives helps managersdetermine what kind of NIS data to collect and whichinventory, survey, or monitoring methods to use. Thedifferences between inventory, survey, and monitoringdata are often misunderstood. Consequently, it maynot be clear to managers how to collect these differenttypes of data, and how to use them in a successfulNIS management plan. In this chapter we defineinventory, survey, monitoring, and other terms commonlyused in NIS management. We then describe howNIS management objectives are used to determine theappropriate inventory, survey, and monitoring methodsfor a management area.DefinitionsWe regard nonindigenous plant species as those that havebeen introduced to a region intentionally or accidentallyby humans (see Richardson et al. 2000 for a completediscussion). The terms exotic, nonnative, invasive, alien, andweed are often used interchangeably. We have attempted toconsistently use the term nonindigenous species throughoutthis book. We caution against invasive as a general termfor NIS until monitoring determines that a particular plantpopulation has been increasing or having an impact (Davisand Thompson 2000), thus making it actually invasive.Considerable confusion also exists about the use of theterms survey, inventory, monitoring, and mapping as theyrelate to NIS. Nonindigenous plant inventories and surveysare observations made at a single point in time to determinethe occurrence (location) of one or more NIS within adelineated management area (NAWMA 2003). The basicgoal of an inventory or a survey is typically to list the speciesor a subset of species (such as noxious weeds) present in amanagement area. It may also include recording the locationof populations of each species. We consider an inventoryto be a cataloguing of the entire management area, whereasa survey is a sampling of a representative portion of amanagement area (Moore and Chapman 1986; Pugnaire andValladares 1999). In this book, when we refer to techniquesthat may be applied to either an inventory or survey, weuse the term inventory/survey. The results of NIS inventories/surveysare normally presented in descriptive reports;in databases, spreadsheets, or tables; and in the form ofmaps, which can be hard copies, geographic informationsystem (GIS) layers, or both. The term mapping is often usedto encompass a range of data-gathering and data-recordingtechniques. In other words, mapping may be used as ageneral description of the entire range of inventory/survey,data-recording, and data-depiction activities.Population is another term that causes confusion whendiscussing inventory/survey or monitoring. We define apopulation or patch as a group of plants of the same speciesdelineated by arbitrary boundaries for the purpose of study(Crawley 1997, p. 364). A group of individuals of the samespecies that are close enough to interbreed (a group ofpatches) is considered to be a metapopulation (Crawley1997, p. 365). An infestation is a large number and/or areaof NIS plants and patches, and is therefore essentially ametapopulation.Monitoring is “the collection and analysis of repeatedobservations or measurements to evaluate changes incondition and progress toward meeting a managementobjective” (Elzinga et al. 2001, p. 2). Generally, monitoringis conducted at regular time intervals at representativesite-specific locations, and can be designed to detectrelatively small changes in the target population (Barbour etal. 1999; Winward 2000). Monitoring methods range fromtaking photographs at designated photo points to collectingdetailed data in fixed plots or along permanent transects(Moore and Chapman 1986; Coulloudon et al. 1999).In this publication, we use monitoring in the specific senseas defined above by Elzinga et al. (2001). However, thoseauthors also point out that the term monitoring is sometimesused in a general sense to describe a broad variety of datagatheringactivities, including inventories and surveys. Weavoid this usage because it creates confusion between twovery important but different aspects of an NIS managementprogram: (1) conducting landscape-scale NIS inventories orsurveys upon which to build and implement an overall NISmanagement strategy, and (2) collection of precise site-specificmonitoring data over time to evaluate the effectivenessof NIS management practices, and/or to determine thespread or ecological impacts of NIS.The major differences between NIS inventories, surveys,and monitoring include objectives, scales, details, precision,and reproducibility of results. Nonindigenous speciesinventories and surveys provide a single point-in-timeassessment of the occurrence of NIS, they often provide dataon the location and overall abundance of an NIS population,and they supply basic information upon which to developNIS management plans. Inventories/surveys are generallyconducted on and interpreted for a relatively large area withconsiderably less detail and precision than that requiredInventory and Survey Methods for Nonindigenous Plant Species