Wide Ecological Amplitude of a Diversity-Reducing Invasive Grass

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The goals of this study were to identify habitats occupied by the Eurasian grass Bothriochloa ischaemum (King Ranch bluestem) on the eastern Edwards Plateau of central Texas, USA, and to measure the effects of this invasive species on plant diversity. A set of descriptive field studies were conducted to determine the relationships between habitat characteristics (woody cover, slope, presence of roads and trails, history of prescribed burning, and presence of grazing) and the presence and abundance of this species. Species richness and diversity of perennial herbaceous species were compared between plots in which B. ischaemum was absent and plots that it dominated.

The only habitat in which B. ischaemum was never found was under the canopies of woody plants. B. ischaemum grew in plots of all inclinations (flat sites to steep hillsides), with little evidence of habitat preference. B. ischaemum was more often, although not exclusively, found in plots near roads, probably because roads facilitate seed dispersal. There was no significant relationship between either grazing or fire history and the distribution of this species. B. ischaemum-dominated plots had lower species diversity and species richness than plots in which no B. ischaemum was found. The results of this study confirm that B. ischaemum is very common on the eastern Edwards Plateau and suggest that it will continue to spread throughout this region and to reduce native herbaceous plant diversity there.

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