When it comes to the environment, Matt Damon said, he's not an expert or someone who stands on a soap box and lectures. But the actor does lend his voice to "The State of the Planet's Wildlife," another installment in PBS' ongoing "Journey to Planet Earth" series.

Damon's narration is just one of several ways he enhances the show, said Hal Weiner, who with his wife, Marilyn, has written, directed and produced the programs and more than 200 other documentaries.

"Obviously Matt is very, very busy," Weiner said, "but when we spend a day or two and discuss the show, he asks questions. He's a good writer. He has suggestions about how to frame an argument, what's best for his delivery. He doesn't just walk in and read the script."

And Damon, who is paid millions for acting in films, has donated his time for the series. "I certainly couldn't afford him," Weiner said.

Damon, an Academy Award winner, said he got involved in the series through Doug Liman, who directed him in "The Bourne Identity." The Weiners' son, Andrew, worked in Liman's office, and Liman suggested that Damon learn about the "Journey" series.

Damon said he read a few scripts and thought they were well done. "They all boil down information in really accessible ways. This one is about wildlife, and there's footage from all over the world," Damon said.

"The State of the Planet's Wildlife" looks at the possibility of a "Sixth Extinction," explaining how vast numbers of animal species could be wiped out in the near future because of poaching, global climate changes, a loss of habitat and other factors.

The program informs viewers about the issues, Damon said, but also points out how some people and communities — in Kenya's Lake Baringo region and in the Florida Everglades, for example — have taken steps to combat problems.

"We're dealing with difficult issues," Weiner said, "so we try to tell a story with dramatic elements. We travel around the world to get a sense of adventure and to help people understand the interconnection and globalization. What happens in China affects the Amazon, and what happens in the Amazon affects people in the United States and Europe."

For the wildlife program, the Weiners and their Washington-based production company, Screenscope, traveled to locations, including South Africa, Brazil, Singapore and the Arctic.

A major observation was realizing the link between poverty and the loss of wildlife, Weiner said.

"When people are hungry, you can't say 'don't poach.' There are some tough questions to be addressed," he said. "These are not easy issues, but we try to explain how local initiatives can go a long way to solving problems."

When it comes to the larger issues of the environment, Damon is sympathetic.

"It's easy to get completely wrapped up in our own lives, dreams and struggles," he said. "But what happens for a lot of people is that they eventually look beyond themselves. They look for ways to make changes in their own lives. ... There are little things, but they have an aggregate effect."