Down by the river( The researchers found species diversit...)

Riparian areas have roughly 40 times greater mean exotic species per plot then upland areas, said Brown.

Even when examining areas with comparable amounts of light availability and soil fertility the results remained fairly similar. As flood frequency decreased, the number of exotic species decreased. But species richness -- the variety of species -- for native and exotics also decreased. According to the researchers these results may be a combination of fewer seeds and less disturbances, leading to fewer opportunities for exotics to invade the upland sites.

Brown and Peet also looked at the results in terms of scale.

Previous research suggests that high species diversity should reduce invasibility because the more species compete in an area, the fewer resources are available to incoming species. Brown and Peets study validated this concept at the small scale. However it did not hold true when they compared diversity of exotic and native species in large scale areas. Brown explains why this is so:

It is possible that we see this phenomenon only at small scales because plants compete at small scales, while at large scales, flooding, variations in seed supply, or variations in resource availability allow the immigration of all types of new species, native and exotic, into the community.

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Contact: Annie Drinkard
annie@esa.org
Ecological Society of America
28-Jan-2003