PARENT SESSION
Poster Session 20: Invasive Species
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

An index of alien species invasiveness (IAI) for assessing vegetation condition.

Magee, Teresa^*,1, Ringold, Paul², Bollman, Michael¹, Ernst, Ted¹, ¹ Dynamac Corporation, Corvallis, Oregon, USA² U.S. Environmental Protection Agency, Corvallis, Oregon, USA

ABSTRACT- Although alien species differ in their capacity to influence ecosystems, the metrics that we commonly use to describe their presence (e.g., alien species number, percent of flora alien, total cover, or relative alien cover) give each species the same weight. Our goal is to develop and demonstrate a metric of plant invasion that reflects the differing capacities of alien species to alter ecosystems. We developed an Index of Alien Invasiveness (IAI) to describe current impact and potential threat of in situ alien species on native vegetation. IAI is scaled from 0 to 100, and incorporates abundance and a score of invasiveness (I_i) for each alien species occurring in a vegetation sample. I_i values were determined by screening each alien species for 24 invasiveness traits in three categories: life history attributes, ecological amplitude, and alteration of ecosystem processes. Riparian vegetation condition was evaluated using IAI for 165 sample plots (30 x 30 m), encompassing 8 species assemblages, and distributed across 1-km reaches of 29 randomly selected wadeable streams in eastern Oregon, USA. IAI values ranged from 0 to 68, with stream reaches and species assemblages of arid, lowland settings more strongly influenced by alien species than those at mesic, higher elevation locations. Regression tree analysis was used to identify conditions where IAI was greatest for the reach scale in our study area. The preliminary model explained 88.6% of the deviance in IAI. Predictors included elevation, size of upstream watershed, mean basal area of trees for stream reach, and percent of forested area or mean annual precipitation in the upstream watershed. Box plots illustrated differences in IAI and relative alien cover between individual streams or species assemblages, and can be used to prioritize conservation or restoration efforts.

Key words: index of alien invasiveness (iai), alien plant species, riparian vegetation, eastern Oregon