Of the 50,000 non-native plant and animal species that have arrived in the United States from foreign countries, many are considered invasive and cost an estimated $138 billion a year in environmental and economic damage.

Environmental Protection Agency chief Mike Leavitt signed new regulations Tuesday aimed at cutting pollutants from diesel engines in off-road vehicles such as farming and construction equipment by 90 percent over the next eight years.

President Bush and Democratic presidential contender Sen. John Kerry of Massachusetts both spoke on the subject of the environment today to mark Earth Day.