Non-Native Plant Invasions in Prairie Grasslands of Alberta, Canada

Abstract

Native prairie grasslands are a fundamental part of Canada's natural heritage, but these formerly extensive ecosystems have undergone declines due to grassland conversion and fragmentation. In addition, remaining native grasslands are threatened by invasive non-native plants, which can outcompete native flora and negatively impact ecological functioning. Although several studies have reported invasions in northern prairie grasslands, only some have investigated patterns across a large spatial gradient, and few have tested their relationship with environmental predictors and anthropogenic disturbance. We surveyed 139 plots across a 938-km spatial gradient in Alberta to 1) identify the most frequent and abundant non-native species, 2) test whether levels of non-native plant invasions are linked to environmental factors or anthropogenic disturbance, and 3) inspect whether relationships differ between mesic and semiarid grasslands. Data were analyzed using generalized additive models and commonality analysis.Our results show that Kentucky bluegrass (Poa pratensis subsp. angustifolia), commonly used for agronomic purposes, is by far the most frequent and abundant non-native plant in Alberta grasslands. Across all plots, abundance and richness of non-native plants were positively linked to a shared effect by aridity, soil texture, and agricultural activity. Furthermore, the importance of predictors differed between mesic and semiarid grasslands. In mesic grasslands, non-native plant abundance and richness were highest in areas with high agricultural activity and fine-textured soils. In the semiarid prairie, topography accounted for most explained variation in the levels of invasion. In summary, climatic conditions, and to some extent agricultural activity and topography, best explain the patterns of non-native plant invasions. A priority for future research is to identify the mechanisms underlying the differences in invasion across mesic and semiarid prairie grasslands. To counteract invasions, practitioners need to diminish the propagule pressure by invasive agronomic grasses, protect and restore grasslands remnants in the mesic region, and proactively control new invaders.