Plants: importance of being economic.

The pulse of the real estate market in a given area turns out to be a powerful indicator of how many exotic plant species have invaded the neighborhood, say two researchers. The hotter the market, the greater the risk to native species from invaders, according to their computer models.

Adding economic factors to a simpler model of alien-plant invasion enhanced the model's predictive power, report Brad W. Taylor of University of Wyoming in Laramie and Rebecca Irwin of Dartmouth College in Hanover, N.H., in the Dec. 21, 2004 Proceedings of the National Academy of Sciences.

The researchers created two models for predicting the number of non-native plant species in a given U.S. state. The simpler model used just U.S. census data plus several ecological factors, such as latitude and the number of native plant species.

The second model incorporated that information plus a measure of economic intensity known as real estate gross state product. It combines such indicators as the amount of new construction and land clearing and numbers of developers, land buyers, and sellers.

The economics-enhanced model predicted 75 percent of the state-by-state variation in plant invasions. The plain population-ecological model predicted only 68 percent, the researchers report. Such models, the researchers say, could be useful for understanding the risk factors for species invasions. --S.M.