The importance of dispersal, disturbance, and competition for exotic plant invasions in Arthur's Pass National Park, New Zealand

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Abstract
This study investigated the effects of disturbance, dispersal, and plant competition on exotic plant invasion. An assessment of the change in species distributions in the Mingha Valley, Arthur's Pass National Park, over five years showed that many species had increased in range, suggesting that dispersal had limited the distribution of these species. The dispersal barrier was removed experimentally by transplanting plants and seeds of Anthoxanthum odoraturn, Holcus lanatus, Cerastium fontanum, and Hieracium pilosella into undisturbed areas. Although transplants of A. odoratum, H. lanatus, and H. pilosella could survive without disturbance, it was essential for the establishment from seed in all four species. These species were therefore limited by the absence of disturbance. A survey of the plant distribution in the Mingha and Edwards Valleys found many exotic species associated with hut, track, and river disturbance regimes. The association of exotic plants with disturbances may be due to the role of disturbance as a window through the barriers of competition, dispersal, and abiotic barriers. The success of these exotic plants in New Zealand seems largely due to success of seedlings of exotic species establishing in areas disturbed by human activity.