Over the past 25 years, more than 36,000 acres of old-growth forests have been destroyed by wildfires at Mesa Verde National Park.

The result, an invasion of aggressive, nonnative plant species that is disrupting the natural plant succession in the parks burned piñon-juniper forest, and those invasive weeds could prevent fully mature forest from ever returning.

To control the invasive nonnative plants, the National Park Service is proposing to develop a new management plan throughout Mesa Verde National Park and Yucca House National Monument.

"Currently the park and monument have known populations of dozens of non-native plants, many of which are highly aggressive competitors with native species," said Mesa Verde spokesperson Betty Lieurance. "Their continued spread puts at risk the ecological and historical integrity of park landscapes."

Park officials say enhancing the strategy to prevent and manage invasive plant occurrences would protect natural communities, ecological processes, cultural resources, visitor enjoyment and other park values.

A plant ecologist at Prescott College in Arizona, Lisa Floyd-Hanna has conducted several studies focusing on fire history and fire effects in piñon-juniper forest. After the 1996 Chapin 5 wildfire in Mesa Verde National Park, she found that seeding with native grass species showed the most pronounced effects in reducing weed density. Herbicide and mechanical treatments were effective in the short-term, according to the study.

"While it cannot be known to what extent the noxious weeds would have spread had we not performed the treatments, it is reasonable to assume that the spatial extent has been reduced by at least the areas treated," she wrote in the study.

Native plants in Mesa Verde National Park include more than 500 species of vascular plants, 75 species of fungi, 21 species of moss and 151 species of lichen. Found nowhere else, a number of rare endemic species also occur in Mesa Verde, some rated by the Colorado Natural Heritage Program as critically imperiled globally.

With a trunk measuring 52 inches in diameter, Colorado's largest Utah juniper tree is also located at Mesa Verde National Park. Another champion juniper at Mesa Verde is dated at 1,300 years old.

There are about 80 species of nonnative plants that have invaded the park, some of which have been classified as invasive, noxious weeds, which by law means they must be controlled.

To aid park officials with best practices to control the weeds, an environmental assessment will be prepared in compliance with the National Environmental Policy Act. The National Park Service is also seeking public participation.

"The public has two opportunities to comment on the project - during initial project scoping and again following release of the environmental assessment," said Lieurance.

Written comments must be received by Feb. 14, and they can be made online at www.parkplanning.nps.gov/meve.

tbaker@cortezjournal.com