The proliferation-decline model of exotic plant invasion.
Otfinowski, Rafael*,1, Kenkel, Norm1, 1 University of Manitoba, Winnipeg, Manitoba, Canada
ABSTRACT- Invasions by exotic plants result in the displacement of native species and the proliferation of exotic monocultures. The success of invaders is frequently attributed to their superior competitiveness. Despite the threat posed by exotic species, current invasion models do not consider the long-term persistence of exotic plant monocultures. In light of recent research, demonstrating negative feedbacks between plants and soilborne pathogens, we propose an alternative model of invasion. Our proliferation-decline model hypothesizes vigorous, initial proliferation of an exotic monoculture, concurrent with a loss of native plant diversity, followed by its gradual decline and limited re-establishment by native species. Our model was tested in the northern fescue prairies (Manitoba, Canada), threatened by invasion of smooth brome (Bromus inermis Leyss.), a Eurasian perennial grass introduced into North America for hay and pasture production. Among smooth brome clones encroaching concentrically into native prairie, clone margins were characterized by high brome productivity and low effective plant richness. In contrast, brome productivity decreased significantly toward clone centers. While this loss of vigor could not be explained by the abundance of plant parasitic nematodes, the accumulation of other soilborne pathogens may play a role in the gradual decline of brome monocultures. This hypothesis is supported by the results of an ongoing greenhouse experiment which demonstrates that pasteurizing soil from clone centers has a greater effect on brome seedling biomass compared to soil collected along clone margins. Our proliferation-decline model of exotic plant invasion, combining vigorous, early proliferation and gradual decline of exotic monocultures, suggests a more intricate pattern of plant invasion resulting from multi-trophic interactions between exotic species and native ecosystems.
Key words: invasive species, biodiversity, soilborne pathogens, productivity
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