HUMAN IMPACTS, PLANT INVASION, AND IMPERILED PLANT SPECIES IN CALIFORNIA.

The article discusses the study on the distribution of 834 of over 1000 exotic plant taxa that have been established in California. Overall species richness increases with net primary productivity. But the exotic flora is richest in low-lying coastal sites harboring large numbers of endangered species, while native diversity is greatest in areas with high mean elevation. Weedy and invasive exotics are more tightly related to the distribution of endangered species compared to the total pool of exotic species. Structural equation modeling shows that while human activities, like urbanization and agriculture, help in the initial invasion by exotic plants, exotics spread ahead of the front human development into areas with large numbers of threatened native plants.