Experimental assessment of the survival and performance of forest herbs transplanted beyond their range limit

Recent anthropogenic climate change is already affecting the range dynamics of many organisms worldwide. Understanding the relative importance of environmental factors and historical processes in determining species' geographic ranges is crucial for predicting the impacts of climate change. Here, we experimentally assessed the survival and performance of four understorey forest plants (Ornithogalum pyrenaicum, Scilla bifolia, Iris foetidissima and Symphytum tuberosum) transplanted beyond their natural range limit over a 7-year period. Since the survival probability of plants transplanted beyond their natural geographic range is expected to decrease with the home-away distance, the species represent a gradient in the distance between the transplant site and their natural geographic range limit (from 50 to 500 km). Three of the four species still survived seven years after introduction. Appreciable survival outside their natural geographic range partly suggests that the ranges of these plant species may be controlled by dispersal limitation. Importantly, an interspecific trend towards decreasing survival with increasing distance from the range limit was apparent. Initial competition from other understorey plants generally limited the survival and performance of the transplanted species. In conclusion, the good survival and performance of the most 'nearby' species emphasizes the importance of dispersal limitation in determining range limits, while the poor survival of the 'farther' species suggests that their occurrence is (co-)controlled by environmental factors such as the local climate. Finally, we briefly discuss our results within the context of human-mediated assisted migration in the face of climate change.