Dispersal limitation and temperature restrict plant invasion in a subarctic treeline environment

Biological invasions are a serious global issue, but invasions are relatively less common at high latitudes, likely due to harsh environmental conditions and limited accessibility. An exception to this is human-settled and disturbed towns that may promote invasions and act as a source of non-native species into the surrounding natural areas. Churchill, Manitoba, Canada (58ºN), is a treeline subarctic town connected by a railway and shipping port, and over a hundred non-native plant species have been recorded within the town footprint and associated areas. While some have persisted for decades in these areas, none has spread into nearby tundra or boreal forest ecosystems, making this an ideal region to investigate barriers to plant invasions. We used a warming experiment to investigate the importance of increased growing season temperatures on three perennial non-native species ( Linaria vulgaris , Plantago major , Taraxacum officinale ), and extended both the spatial and temporal scale to investigate non-native survival and growth across the tundra-boreal boundary over several full years. We found that non-native plants were able to survive after manual translocation into natural areas, indicating that low dispersal is likely a limiting factor to spread. In addition, non-native seed germination was improved in warmer microsites, suggesting that temperature is also a limiting factor. However, survival and growth of these non-native species consistently declined over time, despite experimental manipulations to remove invasion barriers. Future global and climate change that results in higher rates of dispersal and/or increased warming may shift these non-native species from invasion failure to success.