Bitterroot Ecosystem Management Research Project

Chipping Sparrow, Photo by Aubree Benson; Knapweed monoculture; Photo by Dean Pearson

Study Title: Ecosystem Management and Invasive Plants: Weed and Biocontrol Impacts on Small Mammals and Efficacy of Herbicide Treatment for Restoration

Study Coordinators: Dean Pearson and Yvette Ortega, Rocky Mountain Research Station, Forestry Sciences Lab

Research Principals: Dean Pearson and Yvette Ortega, Rocky Mountain Research Station, Forestry Sciences Lab; Regan Callaway, University of Montana

Description: Managers need information to help them choose among alternative management practices to reach their goals. Our research evaluates current weed control strategies in an ecological context. This project focuses on biological control, which is the intentional release of exotic organisms for control of target pest species. We previously documented that Urophora (gall fly) biological control agents increase deer mouse populations because their larvae provide an abundant source of protein in the winter. We also documented that Urophora biological control agents increase the prevalence of Sin Nombre hantavirus by increasing deer mouse populations. A result of increased deer mouse populations is increased predation on native plant seeds and reduced recruitment into those plant populations. We have recently found that using herbicides to suppress spotted knapweed and its gall fly subsidies to mice may reduce elevated levels of seed predation by mice on native plants, but the direct effects of broadleaf herbicides on native forb seedlings may outweigh this positive indirect effect.

Study Title: Impacts of Natural Enemies and Drought on Spotted Knapweed (Centaurea maculosa): Biotic Versus Abiotic Limitation of Invader Success

Study Coordinators: Dean Pearson and Yvette Ortega, Rocky Mountain Research Station, Forestry Sciences Lab

Research Principals: Dean Pearson and Yvette Ortega, Rocky Mountain Research Station-Wildlife and Terrestrial Habitats Science Program, Missoula, MT; Nancy Sturdevant, Forest Health Protection, State and Private Forestry, Northern Region Office, Missoula, MT

Description: Despite much research aimed at invasive plants, we still do not understand what factors determine the success of invaders, distinguishing the strong from the weak. Abiotic factors may play a prominent role in determining the invasion strength of exotic plants and the ability of natural enemies to suppress them, but little research has critically examined this possibility. By understanding the underlying factors driving population status of strong invaders, we can predict which exotic plant species will function as strong invaders and how they may be controlled, greatly increasing the efficacy of weed management programs. This research addresses questions about the separate and interacting roles of biocontrols and abiotic factors, such as drought, on knapweed populations. Field research showed that although spotted knapweed has declined in recent years, it has declined both in the presence and absence of Cyphocleonus achates and other biocontrol agents. This suggests that some other factor such as drought may be the primary cause of this decline. There is some indication that C. achates may have a greater impact on drought-stressed knapweed. We will use garden experiments to explore this possibility more.

Study Coordinators: Yvette Ortega and Dean Pearson, Rocky Mountain Research Station, Forestry Sciences Lab

Research Principals: Dean Pearson and Yvette Ortega, Rocky Mountain Research Station, Forestry Sciences Lab; Diana Six, University of Montana College of Forestry and Conservation

Description: We examined the ecological benefits and costs of broadleaf herbicide treatment, an increasingly prevalent weed control tool, using data from a 6-year study conducted in conjunction with the Lolo National Forest in western Montana. Weed management activities were directed primarily at an aggressive exotic invader, spotted knapweed (Centaurea maculosa). From 1999-2001, we sampled plants, insects, and songbirds at open forest sites that were either invaded by knapweed or dominated by native vegetation. In the fall of 2002, the Lolo National Forest aerially treated four of eight knapweed and native sites, respectively, with the broadleaf herbicide, picloram, and we conducted post-treatment sampling from 2003 through 2005. We considered the following management scenarios: 1) no treatment, to evaluate the no-action alternative, including the impacts of knapweed over time, and 2) weed treatment using broadleaf herbicide, to allow estimation of herbicide effects including benefits of knapweed suppression. This year, we completed a monograph presenting our results within a management framework. This body of work illustrates the critical need to consider how trophic levels interact when documenting the condition of natural systems.

Study Title: Impacts of Invasive Plants on Songbirds: Using Song Structure as an Indicator of Habitat Quality

Study Coordinators: Yvette Ortega and Dean Pearson, Rocky Mountain Research Station, Forestry Sciences Lab

Research Principals: Dean Pearson and Yvette Ortega, Rocky Mountain Research Station, Forestry Sciences Lab; Erick Green, University of Montana Division of Biological Sciences

Description: Our long-term research sponsored by BEMRP indicates that exotic invasive plants like spotted knapweed can significantly impact habitat quality for songbirds like the chipping sparrow. We found that changes in habitat quality induced by spotted knapweed invasion can lead to subtle yet profound changes in songbird populations-we detected no change in abundance of adults in knapweed-invaded habitats compared to those dominated by native vegetation, but documented delays in breeding that led to reduced breeding productivity and increased turnover of adults between breeding seasons. Changes in habitat quality associated with knapweed invasion included declines in native plants that in turn impact insects serving as key food sources for songbirds and other vertebrates. Our research shows how the impacts of invasive plants can ripple through natural systems from plants to insects to songbirds.

Using understandings derived from our long-term research of spotted knapweed, we are testing a novel method for assessing songbird population status and habitat quality that is based on an easily measured parameter-song structure. We are using field data to link changes in habitat quality caused by spotted knapweed invasion to differences in song structure at invaded compared to native-dominated sites. Given the links between song learning, turnover rates, and habitat quality in songbirds, song structure may serve as a new and greatly improved means of monitoring population status, including the impacts of invasive species. Our preliminary analysis indicates that song structure may be an important indicator of habitat quality-songs a sites dominated by native plants species formed cohesive neighborhoods that were more similar to each other than those at knapweed-invaded sites.

Study Title: Rodent Seed Predation as a Biotic Factor Influencing Douglas-fir Encroachment and Ladder Fuel accumulations in Seral Ponderosa Pine

Study Coordinators: Dean Pearson, Rocky Mountain Research Station Forestry Sciences Lab

Research Principals: Dean Pearson and Yvette Ortega, Rocky Mountain Research Station-Wildlife and Terrestrial Habitats Science Program, Missoula, MT; Elizabeth Crone and Rafal Zwolak, University of Montana, College of Forestry and Conservation Sciences, Missoula, MT

Description: This project will quantify the effect of deer mouse seed predation on rates and relative abundance of ponderosa pine and Douglas-fir establishment following fuels reduction treatments of various sizes. We will quantify the spatial aspects of this phenomenon in order to provide managers with guidelines to manage the cumulative effects of rodent seed predation on accumulations of ladder fuels in the wildland-urban interface.

Study Title: Long-term Effects of Thinning and Broadcast Burning on Spotted Knapweed Invasion and Understory Vegetation

Researchers: Dean Pearson and Yvette Ortega, Rocky Mountain Research Station—Wildlife and Terrestrial Habitats Science Program, Missoula, MT; Mick Harrington, Rocky Mountain Research Station—Fire, Fuels, and Smoke Science Program, Missoula, MT

Description: BEMRP’s oldest study site is the Lick Creek Demonstration/Research Forest, which underwent thinning and understory burning treatments in 1993 and 1994. Throughout the years since, scientists have returned to Lick Creek to collect data related to the original objectives, and to capitalize on previous work to answer other questions. In FY 07, we set up a study to examine how ecosystem management treatments affect weed invasion and how this may alter wildlife habitat. We re-measured understory vegetation at the same locations using the same methods as employed in the original study. This will allow us to evaluate how thinning and burning treatments have affected weed invasion over a 15-year time period.