In 2009, Montana's Big Hole staff began monitoring an invasive plant threatening native habitat. 17 years later, spotted knapweed estimates stood at just 8% of its 2012 peak, showing strong control

Managing invasive plants can require years of monitoring, treatment, and cooperation among land-management teams. At Big Hole National Battlefield in Montana, sustained efforts since 2009 have helped reduce a spotted knapweed infestation that threatened both the battlefield’s natural and cultural resources.

Seventeen years after monitoring began, found knapweed population estimates stood at just eight percent of their 2012 peak, indicating major progress in controlling the invasive plant.

Long-Term Efforts Reduce the Infestation

National Park Service staff and the Northern Rocky Mountain Exotic Plant Management Team (EPMT) have played a significant part in minimizing spotted knapweed at Big Hole National Battlefield. Monitoring and control work involving park staff, the Upper Columbia Basin Inventory and Monitoring (I&M) Network, and EPMT staff has been underway since 2009.


The infestation extended through 2012 on the Howitzer Hill and Horse Pasture slopes within the battlefield. Spotted knapweed can threaten cultural and natural resources, including historic viewsheds and the native biodiversity of the site.

Between 2013 and 2018, the Northern Rocky Mountain EPMT, the Upper Columbia Basin I&M Network, and Big Hole National Battlefield staff contributed to attempts that brought spotted knapweed population estimates down to eight percent of the 2012 peak. The 2017 estimate was among the lowest recorded since 2010. Maintaining that downward trend over time remains an important goal.

Targeted Herbicide Applications Support Monitoring

As per the park staff, a creative strategy combining tactical herbicide applications with field monitoring has been central to the control effort.

Park and I&M network staff work in teams to record observations of knapweed and rare plants. At the same time, park staff carry small cans of herbicide, enabling them to spray knapweed plants discovered within or between study plots.

The method is part of a wider collaborative cultural and natural resources management initiative involving various “Crown of the Continent” land management entities.

Teams Study Prescribed Fire and Native Plants

The collaborative project includes park staff, network I&M staff, EPMT, Glacier National Park fire management, and neighboring US Forest Service botanists. The teams are analyzing how prescribed fire affects both spotted knapweed and Lemhi penstemon (Penstemon lemhiensis), a rare endemic plant that grows on the same slopes.

In 2014, teams conducted a burn on part of Howitzer Hill and have continued monitoring the results.

Overall, the study indicates that spotted knapweed is under control and that the impacts of prescribed fire on Lemhi penstemon are acceptable, enabling the rare native plant to thrive.

The findings suggest that prescribed fire may sometimes be useful for maintaining the open hillslope in a condition similar to how it appeared in the 1877 Battle of the Big Hole.

Lemhi Penstemon Population Remains Stable

Researchers are working with the hypothesis that fire could benefit Lemhi penstemon. The plant is thought to favor bare soil on steep slopes for successful germination.

A flush of fresh penstemon seedlings did not appear after the 2014 fire. The unusually hot and dry conditions at the time may have contributed to the lack of new seedlings.

Some mature penstemon plants died after the fire, but mortality was only modestly higher than in unburned portions of the study region.

During the ten years of the study, monitoring estimates showed that the Lemhi penstemon population remained stable at approximately 3,000 plants. It is the largest known population within its geographically-restricted range.

Continued Collaboration

The decline in spotted knapweed illustrates the results of sustained monitoring and control work at Big Hole National Battlefield. Continued collaboration among park, I&M, and EPMT staff is expected to help protect Big Hole National Battlefield and other park units from invasive threats such as spotted knapweed.

The ongoing work also provides continued monitoring of the relationship between invasive-plant control, prescribed fire, and the rare Lemhi penstemon population.

Source: U.S. National Park Service

FAQs:

Q1. What is an invasive plant?

An invasive plant is a plant that can threaten native habitats and other resources. Managing invasive plants can require ongoing monitoring and control.

Q2. Why is monitoring important?

Monitoring helps teams track changes in plant populations over time. It can also help assess the results of management efforts.