Research Overview:

Chris Larson

Broadly speaking, my research focuses on restoring Montana rangelands that have been impacted by plant invasions. This broad goal can be separated into three separate projects that address different threats to Montana rangelands.

My first project focuses on restoring degraded sensitive and unproductive Montana agricultural land. The federally funded conservation Reserve Program (CRP) is designed to compensate landowners through rental payments and cost-share assistance while increasing the long-term sustainability and ecological health of environmentally sensitive agricultural land. Historically, much of the older CRP land was planted to aggressive non-native perennial plant species (e.g., Agropyron cristatum) to reduce soil erosion. These near monocultures substantially alter their ecosystems and have considerable implications for multitrophic biodiversity. For this project, my research integrates management tools (chemical, mechanical, cultural) with native seeding to reduce the dominant non-native species (A. cristatum) and increase above- and below-ground biodiversity. Establishing native species after A. cristatum management is difficult, therefore I am also investigating A. cristatum’s rhizosphere community and its potential impact on soil conditions, which may inhibit seedling establishment and early growth.

My next area of research is Bromus tectorum’sinvasion of Montana rangelands. Bromus tectorum is a non-native invasive annual grass introduced to the American West in the 1860’s. Since its introduction, B. tectorum has proliferated throughout the region, especially in rangelands, substantially altering their structure and degrading their function. This area of research has two separate projects. The first project addresses the response of B. tectorum to fire and severe soil disturbance, both of which have been associated with B. tectorum’s expansion in the region. Bromus tectorum is a winter annual, which means it establishes in the fall, has extensive root growth during the winter, early shoot growth in the spring, and early senescence in the summer compared with the competing native species. The early senescence of B. tectorum provides a layer of fine litter, which can be fuel for wildfire, which has resulted in larger and more frequent fires. The increased magnitude and frequency of these fires can impact native plant communities, making them more susceptible to degradation after disturbance, which can in turn increase B. tectorum in these burned areas. While much of the evidence supporting this B. tectorum-fire positive feedback is from the Great Basin and other warm and dry regions of western N. America, there is concern that B. tectorum will expand after fire in Montana rangelands. The goal of this project is to assess the plant community dynamics and recovery (including B. tectorum abundance) 13 years after a Montana rangeland fire and accompanying severe soil disturbance. The second project in this research area is focused on managing B. tectorum after severe soil disturbance using integrated management, and how baseline B. tectorum state (abundance) interacts with management. Bromus tectorum management recommendations often use different baseline states (e.g., ‘mild’, ‘moderate’, ‘dominant’) to prioritize management. However, there are few empirical data supporting these recommendations. The goal of this project is to investigate how integrated management (targeted grazing + herbicides), and initial B. tectorum state interact to shape community recovery (native community, B. tectorum) eight years after management and 13 years post disturbance.

Lastly, I have a research project focused on restoring Montana rangelands threatened by conifer (e.g., juniper, douglas fir) encroachment, and the potential impacts conifer management practices may have on invasive herbaceous species. Fire suppression practices have altered the natural fire regime of many rangelands, which has resulted in conifers expanding into these areas, substantially altering their plant community composition, biodiversity, and reducing forage quality and quantity. To address this threat, the Bureau of Land Management has begun to remove conifers from these areas; however, the methods of conifer removal can be highly disruptive and destructive, and there is concern that these methods will facilitate the invasion of these lands by non-native invasive plant species, especially B. tectorum. For this project, my research focuses on monitoring plant community change following conifer removal and assessing the effects of herbicide application and post-treatment seeding on the recovery of the impacted rangelands.