| Summary: | The number of introduced plants species in Churchill Manitoba has fallen from 104 to 36 between the sampling periods of 1989 and 2013 despite continued climate warming which is predicted by theory to allow for easier establishment of new species in harsh environments. My work suggests that introduced plants are, in general, favouring warmer, ameliorated sites, with higher average soil nutrition that have been disturbed by human activities. This work has found two novel and important differences from the 1989 survey in that continuous disturbance is no longer required for introduced species to persist, and one introduced plant, Taraxacum officinale, has begun growing in two undisturbed locations. Climate warming as well as the invasional meltdown hypothesis can explain these two new observations. The decline in introduced species diversity can in large part be explained by the removal of barley from grain shipments to the Churchill grain elevator, although the study was confounded by a low precipitation summer which could have impacted the number of introduced species that germinated and grew in 2013. The drop in introduced species diversity despite a warming climate is evidence that many of the plants recorded as occurring in Churchill were ecologically doomed populations only kept in existence through constant seed subsidies from the grain elevator.
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