Across the western U.S., climate change and disturbances like wildfires, drought and insect outbreaks are already reshaping ecosystems. Landscapes that are no longer able to support the vegetation they once did are transforming into different states. For example, in a warmer and drier climate, tree seedlings may have difficulty regrowing following a wildfire, causing a previous forest ecosystem to transition into a grassland. As these pressures intensify, scientists and resource managers are faced with tough decisions about how to steward ecosystems and the species they support into the future.

Source: U.S. Forest Service

A new, NW CASC-supported study led by researchers at the University of Montana and partners in the U.S. Forest Service, Conservation Science Partners, and Vibrant Planet, uses climate-analog modeling to explore the future of vegetation change in the western U.S. This study found that about one third of the western U.S. is highly vulnerable to ecological transformation by the middle of the 21st century, and that more than any other vegetation groups, subalpine forest and alpine ecosystems are most at risk of declining by mid-21st century. The findings from this study are published in an open-access paper in Global Change Biology and are presented in a free, web-based tool, which can help land managers understand management options in a given area. An accompanying data story, developed by Vibrant Planet Data Commons, breaks down the paper and web tool into key takeaways and describes management applications.

As intensifying disturbances like wildfire, drought and insect outbreaks alter the landscape, and changing climate conditions affect what grows back afterwards, land managers need nuanced tools, like the climate-analog modeling approach, to understand how to steward ecosystems into the future. For any given study location, this approach identifies climate analogs, or places already experiencing the future climate (mid-21st century) of the study location. Since these comparable, or analog, locations are in the same geographic region and contain the same pool of species, they can be used to project the types of vegetation that the study location may support by the mid-21st century.

For any given study location, this approach identifies climate analogs, or places already experiencing the future climate (mid-21st century) of the study location. Since these comparable, or analog, locations are in the same geographic region and contain the same pool of species, they can be used to project the types of vegetation that the study location may support by the mid-21st century. 

While other models that project future vegetation assign a single type of vegetation to a location, the climate-analog modeling approach accounts for more complexity. Recognizing that a given set of climate conditions can likely support multiple types of vegetation, this approach provides a range of possible vegetation outcomes, instead of a single, deterministic one. The model ranks these analogs based on how closely each one matches the study location’s future climate. The vegetation type with the closest climate match becomes the primary projection, while the second closest becomes the secondary projection. The model doesn’t take into account ecological processes like disturbance, dispersal or competition, thus is meant to complement the knowledge of local land managers.

The web application that accompanies this study can be used to translate the findings from the model into planning and decision making contexts. In addition to seeing the primary and secondary vegetation projections, one can use the tool to see the vulnerability of an area to change. Vulnerability ranges from low, where future vegetation resembles the current vegetation, to very high, in which a substantially different vegetation community is projected. The tool can also show the level of agreement, or how closely the climate analogs align on the primary projection. High agreement means there’s a higher likelihood that a landscape will transform to the vegetation type in the primary projection, while low agreement suggests that multiple vegetation types are nearly equally supported, and that factors unrelated to climate (e.g., disturbance, management actions) will help determine which vegetation type results. Based on these measures of vulnerability and agreement, the data story provides a matrix of four decision-making contexts that managers can use to guide their actions. Additionally, the data story explains how the vegetation futures tool can map onto the Resist-Direct-Accept Framework, to help land managers make informed and strategic choices about how to steward transforming ecosystems.

Source: Natural Resources Conservation Service, Oregon

The project team sought input from a broader group of state, federal, nonprofit and Tribal partners throughout the research process, which informed what types of climate and vegetation data were used, the distance to analogs, and web tool functionality, among many other facets of the research. Overall, the study found widespread vulnerability, or a high potential for transformation by the mid-21st century, in vegetation communities across the study area, spanning approximately 3.2 million km² of forests, woodlands, shrublands and grasslands from the Pacific Coast to the Rocky Mountain Front. Though the findings show that the relative proportions of the area suitable for each vegetation group are mostly stable, the redistribution of vegetation types is widespread at 40%. This wide redistribution of ecosystem types will lead to new combinations of species and interactions on the landscape and changes to ecosystem function, which could negatively impact the ability of ecosystems to provide benefits that people depend on.

Since projections of future vegetation do not often account for the complexity present on the landscape, this study’s approach for projecting future vegetation change embraces complexity and nuance that can support place-based decision making, especially when paired with climate adaptation decision-making frameworks like Resist-Accept-Direct. This new suite of information and tools provides land managers in the western U.S. with a pathway for navigating vegetation transformations into the future.

Open-Access Publication

This open-access paper in Global Change Biology, Alternative Future Vegetation Pathways Reveal Potential Transformations of Western US Ecosystems, dives into the methods and findings of this study.

Read the Paper

Web Tool

The Vegetation Futures Tool is designed to support decision making around vegetation transitions. Users can toggle variables on and off, compare between current and future conditions, and generate figures and reports for a specific area.

Explore the Tool

Data Story

The Alternative Futures Data Story, hosted by Vibrant Planet, breaks down the science from this study with maps, visuals and narratives, and links to a suite of climate-analog models, associated datasets, and the interactive web application.

Explore the Data Story