WASHINGTON -- President Obama and Vice President Joe Biden are watching former President Bill Clinton plant trees at a national park site along the Anacostia River in northeast Washington.

The stop Tuesday at the Kenilworth Park and Aquatic Gardens came after Obama signed into law a bill to expand opportunities for people to serve their communities. It also triples the size of the AmeriCorps program over eight years.

Obama and Biden were joined by their wives and volunteers from the Student Conservation Association and local public high schools.

The association's volunteers annually provide more than 2 million hours of conservation service at sites in all 50 states.