The federal and state departments of agriculture, national and state park systems, and The Nature Conservancy devote large and increasing resources to efforts to control exotic plant species. Hundreds of grassroot groups selectively address the problem in specific areas, but their work is dwarfed by the magnitude of the overall problem. Taxpayers have spent billions of dollars purchasing and protecting wildlands which are now being lost due to invasion by weeds. Economic return is reduced in areas dominated by weeds. For example, in addition to the above-cited California grazing lands degraded by the spread of yellow star thistle, a public agency was successfully sued by an adjacent landowner because yellow star thistle invasion rendered the home unsaleable.
Undesirable plants continue to be introduced to California.
Biologists consider it a threat to the desert tortoise. With increased international travel and trade, new accidental and intentional introductions will likely accelerate. Ecosystem function is altered, often irreversibly, by exotic plant invasions. Other exotic plants have dramatic effects on hydrological regimes and nutrient cycling. Non-native plants modify wildlife habitat, altering the species composition, sometimes drastically.