Invasive species threaten Yosemite ecosystem


Yosemite is home to countless plants and animals all living in balance to create this wonderful place. But while many visitors think bears are the biggest threat, it's what's sprouting up that is threatening the park's delicate ecosystem.

"Whenever you have invasives it affects the entire food chain, no matter whether it is a plant or an animal," said Niki Nicholas, Ph.D. with Yosemite National Park.

Nicholas oversees the natural resources within Yosemite National Park, including the 160 plant species that don't belong there.

"They sometimes can bring other diseases into the park, they can change the fire regime in the park. We are in a fire dominated ecosystem here. They can change the visitor experience," said Nicholas.

She estimates that as much as 5 percent of the park has been taken over by invasive plant species. That may not seem like very much, but when you consider that Yosemite National Park is roughly the size of Rhode Island, you get a better picture of the enormity of the issue.

Nicholas says many of the seeds that infect the park are brought in unknowingly by visitors.

"For a lot invasive plant species, they sometimes come in on the tires of cars, they sometimes come in on the bottoms of people's feet, sometimes they just blow in," said Nicholas.

Volunteers and park staff are weeding out Himalayan blackberry and pulling the plants out by hand.

"We just take off chunks at a time, chunks at a time, until we're completed with one area and then we move to another area," said Ranger Adam Mates.

Trimming them down to the ground keeps them from crowding out plants that belong there.

"I know it's going to come back, but the bigger picture of it is that we're reducing it, we're taking away its viability to seed out for the next several years and hopefully we're hurting it some so it's not as aggressive as it is," said Ranger Mates.

In just one day, rangers were able to keep the area from being taken over. Rangers hopes to keep it from coming back for good. The park service recently released its Invasive Plant Management Plan, outlining a range of alternatives.

"We want to do more than just suppress our invasive plants, but eradicate them," said Nicholas.

Doing so may ultimately include the limited use of herbicides -- a controversial prospect for nature purists. Final approval of the plan is expected by October.

"Our goal is for park visitors to come into the park and not see exotic species and not have the ecosystem impacted by exotic species," said Nicholas.

Assuming the eradication plan in approved, Nicholas is confident they'll be able to weed out the bulk of the invasive plants within the next five years.

Plants are not the only problem in the park. Up until 20 years ago, the park stocked some lakes with fish for sport. Those fish are now preying on some of the native species, including young frogs and the insects they eat. A plan is currently in the works to deal with that problem.

Written and produced by Ken Miguel.

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