Clark Bunting, president and CEO of the National Parks Conservation Association, is stepping down/NPCA

Clark Bunting, who came to the National Parks Conservation Association from the Discovery Channel a little less than two years ago, is stepping down as the park advocacy group's president and CEO.

In a note to NPCA's national and regional council members, Fran Ulmer, president of the non-profit's board of trustees, said "some ongoing health issues on the home front" convinced Mr. Bunting that he could not fulfill his role.

"I regret this decision – which was not made lightly by him - but I understand it," Ms. Ulmer said in her note. "Clark has been our leader for nearly two years, and during that time he has made some significant and strategic changes. He has pushed the organization to speak more emotionally and simply about the good work that you all do to protect our national parks..."

She also cited his work in negotiating a contract with Subaru of America and working with television networks to air NPCA's public service announcements about the national parks.

No immediate successor was named.