Mapping ecological states in the upper Colorado River basin: Implications for fire management

Authors: SEVERSON, JOHN - Us Geological Survey (USGS); BISHOP, TARA - Utah Valley University; KNIGHT, ANNA - Us Geological Survey; NAUMAN, TRAVIS - Natural Resources Conservation Service (NRCS, USDA); McNellis, Brandon; VILLARREAL, MIGUEL - Us Geological Survey (USGS); REED, SASHA - Us Geological Survey (USGS); Young, Kristina; BRUNSON, MARK - Utah State University; DUNIWAY, MICHEAL - Us Geological Survey (USGS)

Submitted to: Applied Ecology and Environmental Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2025
Publication Date: 8/7/2025
Citation: Severson, J.P., Bishop, T.B., Knight, A.C., Nauman, T.W., McNellis, B.E., Villarreal, M.L., Reed, S.C., Young, K.E., Brunson, M., Duniway, M.C. 2025. Mapping ecological states in the Upper Colorado River Basin: Implications for fire management. Applied Ecology and Environmental Research. 4(3):035004. https://doi.org/10.1088/2752-664X/adf55f.
DOI: https://doi.org/10.1088/2752-664X/adf55f

Interpretive Summary: This study aims to create detailed maps showing how plant communities have changed over time in a semi-arid region of the Upper Colorado River Basin. The area has seen major ecological changes due to increased fires and the spread of invasive plant species since the 1990s. The researchers used maps, field data, and satellite images to track these changes from 1986 to 2022, focusing on two types of land areas with similar climate and soil conditions. They found that invasive species have dramatically increased, replacing native grasslands and shrublands. These invasive areas also burn much more frequently than other plant communities. In contrast, drought has led to more bare ground and grasslands but has reduced the spread of invasive species in some cases. The findings show how fire, drought, and plant invasions are accelerating changes in this important region, highlighting the need for better management and conservation strategies to address these shifts. The study also provides new tools for monitoring these changes at a large scale, helping inform land management decisions.

Technical Abstract: Spatially explicit information on ecosystem dynamics that offers a mechanistic understanding of ecological processes can benefit environmental management. Broad-scale maps based on state-and-transition models provide valuable insight into transitions among ecological states resulting from specific drivers within areas sharing similar climatic and edaphic characteristics ecological sites (ES). We aimed to quantify ecological dynamics of two ES groups in the Upper Colorado River Basin from 1986 to 2022 through annual maps of ecological states and assess potential drivers of observed state change. This region comprises important sagebrush shrublands and pinyon-juniper woodlands affected by non-native annual grass invasion, wildfires, and drought-induced tree mortality. Using field-based and remote sensing data, we modeled vegetation states using random forest models and mapped the states annually from 1986 to 2022. To demonstrate the utility of the state maps for monitoring and management, we used this time series of maps to investigate the influences of fire and drought on state occurrence. Our findings revealed a statistically significant increase in states invaded by non-native annual species (Invaded state), which replaced Grassland and Shrubland states, while Shrubland states decreased significantly, transitioning to invaded and Woodland states. Invaded states had the highest likelihood of burning, followed by Woodlands. Drought was associated with increased area of Grassland and Bare states, but with decreased area of invaded and Shrubland states. These results indicate an accelerating fire cycle is potentially leading to ongoing regional environmental degradation. Despite increasing drought conditions during the study period, the invaded states continued to increase in area, indicating additional underlying mechanisms. Our reproducible, broad-scale, ecologically-driven state mapping process enhances understanding of how drought, fire, and invasion by non-native plants can transform semiarid landscapes of the western USA.