Non‐native species threaten the biotic integrity of the largest remnant Pacific Northwest Bunchgrass prairie in the United States

Abstract

Questions: The Pacific Northwest Bunchgrass ecosystem is one of the most endangered in the United States, yet community-level patterns of non-native plant distribution and abundance remain largely unexplored. To address this information gap, we asked the following questions: What are the distinct plant communities within Zumwalt Prairie Preserve? What are the most widespread and abundant non-native species and how does non-native species composition and dominance vary across plant communities? How do historic land use, biotic and environmental factors influence plant community composition, particularly in terms of non-native species abundance and dominance? Location: Zumwalt Prairie Preserve, Wallowa County, Oregon, USA. Methods: We sampled 123 plots using point-intercept methods within a stratified random sampling approach. We analyzed community variation using cluster analysis, indicator species analysis, and non-metric multidimensional scaling, and related composition and non-native plant abundance to historical land use, biotic and environmental variables using joint plots, linear regression, and non-parametric multiplicative regression. Results: While native perennial grasses were the most abundant species, non-native species accounted for 27% of species encountered and four of the ten most abundant species were non-native annual grasses (e.g., Ventenata dubia) or non-native perennial grasses (e.g., Poa pratensis). Abundance patterns of non-native perennial grasses differed markedly from those of non-native annual grasses; non-native perennial grasses were concentrated in old fields, while non-native annual grasses were abundant in moisture-limited uncultivated sites. Conclusions: Despite its protected status, non-native plant species pose a serious threat to the biotic integrity of the Preserve, with unknown consequences to ecosystem dynamics and function. Moreover, patterns of non-native abundance vary considerably, with different species responding individually to land-use, environmental, and biotic gradients. An improved understanding of the relationship between non-native species distributions and historical, environmental, and biotic factors can help in the development of ecologically appropriate, cost-effective strategies for the conservation and restoration of this unique landscape.

Citation

Endress, Bryan A.; Averett, Joshua P.; Naylor, Bridgett J.; Morris, Lesley R.; Taylor, Robert V. 2020. Non‐native species threaten the biotic integrity of the largest remnant Pacific Northwest Bunchgrass prairie in the United States. Applied Vegetation Science. 23(1): 53-68. https://doi.org/10.1111/avsc.12464.