Inventory and Survey Methods for Nonindigenous Plant Species (PDF)

Chapter 10 • Beyond Inventory/Survey and Monitoring: Risk Assessment and Managementwere assigned to four levels of risk: none, low, moderate,and high (Table 1). A risk map for potential sulfur cinquefoilspread in SEFR was then developed (Figure 2). The risk mapindicated that 41%, or 5,526 ha (13,654 acres), of SEFR issusceptible to invasion by sulfur cinquefoil; of this, 5% ofSEFR is at high risk, 21% is at moderate risk, and 15% isat low risk of invasion. The risk assessment also providesadditional information about at-risk areas (Table 2). Forexample, 61% of bluebunch wheatgrass grasslands are atmoderate or high risk of invasion, while over 95% of Idahofescue (Festuca idahoensis) grasslands, which make up lessthan 3.2 ha (8 acres) within SEFR, are at moderate or highrisk of invasion. This type of information can be valuable forland managers, particularly when assessing threats to rare orsensitive habitats or plant communities, or when managersare estimating costs of control or prevention efforts andprioritizing management activities of an area.▲ Figure 2. Risk map for sulfur cinquefoil (Potentilla recta)invasion in Starkey Experimental Forest and Range. Risk levelswere assigned on the basis of site susceptibility, disturbancehistory, and proximity to current infestations.infestations: (1) high exposure: areas within 500 m (1,640ft) of current infestation, (2) moderate exposure: areas from500 to 1,000 m (1,640 to 3,281 ft) from infestation, and (3)low exposure: areas farther than 1,000 m (3,281 ft) from acurrent infestation.Developing a Risk MapA risk matrix was then constructed based on the susceptibility,disturbance, and proximity classifications, and areasAdditional Approaches to Risk AssessmentNIS risk assessments can be performed in a variety ofways. For example, although our approach identified areassusceptible to invasion by using regional reports of occurrenceof sulfur cinquefoil in specific plant communities,a different variable could have been used to assign levelsof susceptibility, such as percent tree canopy cover. Inanother area of the Blue Mountains, data indicates thatsulfur cinquefoil rarely infests areas with more than 50%canopy cover (Endress, unpublished data). Thus, we couldhave used this variable to classify susceptible areas. Clearly,a wide range of variables (e.g., canopy cover, soil, slope,disturbance) or combinations of variables could be used toassign levels of site susceptibility if the variable(s) predictablyinfluence the likelihood of invasion, and the data areavailable for inclusion into a GIS database. In the case ofsulfur cinquefoil, existing plant community informationwas used because it was the most current data available,and because existing vegetation often incorporates a suiteof environmental variables such as soil type, elevation, andprecipitation. We used disturbance in our model becausesulfur cinquefoil invasions are associated with areas ofvegetation and/or soil disturbance (Rice 1999; Zouhar 2003).Additional components can also be included whenassessing NIS risk. For example, an NIS risk assessment fornorthern Idaho and western Montana included a “threat”component, which ranked plant communities accordingto the degree of change to their structure, composition, orfunction as a result of an invasion (Mantas 2003). This componentcould be a useful addition to our model because bothmixed conifer forests and bluebunch wheatgrass grasslandsare susceptible to sulfur cinquefoil invasion; however, thedetrimental effects of the invasion are likely to be greater in72Inventory and Survey Methods for Nonindigenous Plant Species