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Are community structure and susceptibility to invasion related? Analysis of 50-year old permanent plots.
KLEPEIS, DEBRA1, BLACK, R. ALAN1, 1
ABSTRACT- We analyzed 35-50 year old permanent plots in steppe communities of eastern Washington to determine the extent of non-native species invasions in these originally pristine communities. Plots were found in three habitat types (h.t.), Artemisia tridentata / Pseudoroegneria spicata h.t., Pseudoroegneria spicata / Festuca idahoensis h.t., and Symphoricarpus albus / Festuca idahoensis h.t., which cross an environmental gradient with a corresponding diversity gradient. We employed methods identical to original work by R. Daubenmire and found that native species cover and frequency declined in all habitat types. Non-native species increased resulting in increased species diversity for our data compared to Daubenmire's data. We found no correlation between non-native species richness and diversity. The driest habitat types, Artemisia tridentata / Pseudoroegneria spicata h.t. and Pseudoroegneria spicata / Festuca idahoensis h.t., had comparable species diversity, but different non-native species richness (9 and 29, respectively). The most diverse habitat type, Symphoricarpus albus / Festuca idahoensis h.t. had comparable non-native species richness (27) to the less diverse Pseudoroegneria spicata / Festuca idahoensis h.t. In all habitat types, cover and frequency of at least one original dominant species significantly decreased. Despite changes in community structure, Principal Components Analysis and Discriminant Function Analysis suggested that the original classification of these three distinct habitat types was still supported by our data. There was a trend, however, for the two driest habitat types to merge in this study.
KEY WORDS: community invasibility, permanent plots, eastern Washington, invasive species