Competitive Effects Of Increased Plant Species Richness And Increased Endemic Versus Native Generalist Species Dominance On The Invasive Grass Microstegium Vimineum During Oak Woodland Restoration
The hypothesis that species-rich assemblages are resistant to invasion by non-native species has generated considerable research and controversy. However, the relevance of such research to the conservation of biodiversity is questionable, given that local species richness often does not correlate with regional or global species richness, two metrics undoubtedly important to conservation. Furthermore, species of greater conservation interest (i.e. endemics) and widespread generalist species may compete differentially with non-native invasive species. To test whether plant species richness or species fidelity to a regionally rare habitat were more important in competitively suppressing an invasive species, I established a field competition experiment in an oak woodland in north-central Mississippi (USA) between the non-native invasive grass microstegium vimineum and six native plant species of varying fidelity to fire-maintained open woodlands. Using a split-plot design, dense, established patches of microstegium were treated with one of the three following native planting treatments or control: (1) a six species polyculture, (2) a monoculture of six individuals of a single species, or (3) a control simulating the soil disturbance of the plantings. I then monitored microstegium percent cover through the 2015 growing season and into the spring of the following year. Emergence of the native species in the spring of 2015 was high (85% survival), which in turn appeared to initially suppress microstegium seedling cover. This initial suppression of microstegium was variable, with the native generalist species outperforming natives that are more highly indicative of open woodlands (i.e. endemics). However, subsequent survival of all native species through 2015 was relatively low (38%), and there was no evidence of suppression of microstegium either in the fall of 2015 or in the spring of 2016. Overall, these results indicate that of the six native species utilized here, the generalist species more indicative of disturbed habitats, yet also of less value to conservation, were more successful at reducing the emergence of this highly invasive grass. However, results also suggest that such a highly competitive invader may ultimately establish and proliferate, regardless of any initial resistance from resident species, possibly to the detriment of regional and global biodiversity.
Biodiversity, Competition, Endemic, Invasion, Species Richness, Ecology and Evolutionary Biology
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