Abstract
Invasive species represent a threat to many ecosystems but are nearly absent from arctic and subarctic Canada. The treeline town of Churchill, Manitoba, has an unusually high number of invasive species due to the presence of a grain port and railway, but few of these species have spread to the surrounding tundra; for instance, common dandelion (Taraxacum officinale) currently is restricted primarily to town, in contrast with its native congener, Taraxacum lacerum. To investigate whether the distribution of T. officinale is affected by the tendency of buildings to create warm, sheltered microenvironments, we surveyed the abundance of both dandelion species relative to existing structures in town. We established transects extending up to 5 m from each side of 23 buildings, and recorded the number of plants in 50 cm x 50 cm quadrats along each transect. We found that T. officinale performed better on the south sides of buildings, that flowering decreased away from buildings, and that these effects were stronger for T. officinale than the native T. lacerum. Soil temperatures were warmer on the south ratherthan on the north-facing sides, providing a possible explanation. Our results show that the distribution of T. officinale currently is more influenced by human-created microclimate compared to the abundance of its native relative. However, T. officinale may spread beyond these refuges as the climate continues to warm.