PORTLAND, Ore. -- It's a case of kill or let kill.

A Portland parks leader wants to hire a crew of 70, full-time and permanent, to do nothing but kill English Ivy.

The ornamental plant threatens to kill the trees of the city's 5,000-acre Forest Park and turn it into an "ecological dead zone," said Michelle Bussard, executive director of the Forest Park Conservancy.

The ivy hit squad would cost $1.5 million a year, she estimated.

"If we don't get serious, we won't have a Forest Park in 60 years," she said during a recent walk in the park.

"Leaving it alone was once a great sentiment," she said "Our leaving it alone has created the problems we now face."

Forest Park accounts for about half the city's parks and natural spaces. The city manages it, the conservancy supports it.

The park turns 60 this year and is showing signs of age.

It faces pressure from nearby residential development and increased use of the 75 miles of trails.

And there's a steady invasion of nonnative weeds, primarily the ivy.

Stephen Hatfield, the conservancy's stewardship director, said ivy starts climbing trees with vines no thicker than a pen. But over years, clumps can grow as thick as a man's thigh.

"Most people think of ivy as ornamental," he said. "We've been groomed to think of it as a nice plant. But this ivy will spread through the park and kill the trees. What we'll be left with is a sea of ivy."

Astrid Dragoy, a city parks bureau manager, said the city plans to use the park's birthday to focus on the challenges facing it.

"It's something people take for granted," she said. "It's the largest urban park in a city limits in the United States. The daunting reality is that we as Portlanders are the owners."