Where There’s Water, There’s Life

TRENDS IN MESIC RESOURCE PRODUCTIVITY HIGHLIGHT AGRICULTURE'S ROLE IN SUSTAINING SAGEBRUSH COUNTRY 

In the sagebrush biome, water is precious. It’s also rare. Mesic resources—areas where water meets land, like riparian zones along streams and rivers, wet meadows, seeps and springs, and flood-irrigated pastures—play a critical role for wildlife and livestock (Figure 1; left panel). In fact, 80% of sagebrush country’s wildlife rely on mesic resources at some point in their annual life cycle, even though these areas make up 2% of the landscape. 

Mesic resources are particularly important later in the summer when upland vegetation communities dry out and become significantly less productive. Given their importance for both wildlife and livestock, understanding long-term trends in mesic resource productivity is critical for improving biome-wide management of these life-sustaining resources.  

A WLFW-affiliated research team, led by Kristopher Mueller, explored how late-season (July 15-September 30) mesic resources have responded to drought and human activities over the last 40 years across 10.62 million acres of the sagebrush biome (Figure 1; right panel). 

Their findings, published in Ecological Indicators, reveal a profound shift in how Western mesic resources behave under drought—and highlight the indispensable role of cattle ranching and private working lands in buffering the West against climate shocks.

From 1984 to 2003, fluctuations in mesic resource productivity—measured using the Normalized Difference Vegetation Index (NDVI) as a proxy for vegetation greenness—were largely explained by drought severity (using the Palmer Drought Severity Index [PDSI]; Figure 2; left panel). However, in the last 20 years, from 2004 to 2023, this relationship weakened and productivity maintained or increased through persistent drought conditions (Figure 2; left panel).  

Despite the decoupling of mesic resources productivity from meteorological droughts, the authors argue that mesic resources productivity is not necessarily stable across the biome. This apparent resilience, they argue, is not intrinsic to the ecosystems themselves, but instead, reflects the increasing role that agricultural production plays in sustaining mesic resources. 

The research highlights the critical role that irrigation (primarily flood irrigation) plays in maintaining mesic resources throughout the sagebrush biome (Figure 2; right panel). When examined spatially, large agricultural valley floodplains act as rancher-assisted refugia, sustaining productive mesic resources through flood irrigation and subsequent groundwater recharge into late summer, especially over the last 20 years when productivity has increased despite persistent drought.

These working landscapes, largely dedicated to hay production for livestock, help buffer mesic resources from drought while maintaining open spaces and accessible forage for wildlife like migratory big game and sage grouse. Flood irrigation also helps recharge groundwater and keeps moisture in the soil where it remains available for vegetation production late into the season. 

Because flood-irrigated mesic resources are largely contained on private lands, are spatially concentrated, and are sustained through agricultural production, the authors highlight that strategic multi-jurisdictional partnerships are critical to preserving these hydrological benefits as water policy tightens. Where agricultural water use is limited, process-based restoration is needed to retain water on the landscape.

Historically, late-season mesic vegetation was almost entirely at the mercy of precipitation. From 1984 to 2003, late-season mesic greenness was tightly linked to drought severity: PDSI explained 92% of the variation in mesic productivity (Figure 2). When meteorological drought hit, wet meadows and riparian areas dried up. However, over the last two decades (2004–2023), this relationship decoupled dramatically, with PDSI explaining only 55% of variation. Remarkably, late-season mesic productivity maintained or even increased across many areas despite persistent, multi-year megadroughts (Figure 2; left panel).

This research further highlights that proactively working with livestock producers is a key strategy for balancing agricultural and ecological water needs across sagebrush country. NRCS’s Framework for Conservation Action in the Sagebrush Biome provides a voluntary, incentive-based, strategic approach for conserving mesic resources on private lands. 

Even with voluntary, incentive-based strategies in place, proactively addressing mesic resources degradation across the biome requires an understanding of where restoration opportunities exist within the broader context of sagebrush ecological health. WLFW’s free and online Mesic Analysis Platform (MAP) delivers three modules that allow just this. 

Through MAP, conservation planners can examine mesic resource persistence at watershed, landscape, and valley-bottom scales, while also visualizing land ownership, proximity to Core Sagebrush Areas delineated in the Sagebrush Conservation Design, and other components of the broader landscape. The tool helps move conservation planning to resource prioritization and ultimately on-the-ground implementation. Watch a recent WLFW webinar about the MAP here.

SHIFTING RESILIENCE: TRENDS AND PREDICTORS OF MESIC RESOURCE PRODUCTIVITY IN WESTERN U.S. RANGELANDS

Abstract: Mesic resources, the late-season herbaceous vegetation found in riparian areas and wet meadows, provide disproportionately important forage and habitat across western U.S. rangelands, yet their response to climatic variability and anthropogenic influences remains poorly understood. Using a 40-year Landsat time series (1984–2023), we quantified trends in late-season productivity (NDVI) across 4.3 million hectares of the sagebrush biome and applied random forest models to distinguish between temporal and spatial predictors of mesic resource productivity. We identified a shift in how mesic resources respond to drought: from 1984 to 2003, mesic productivity was largely explained by drought severity (Palmer Drought Severity Index, R² = 0.92), but this relationship weakened in the next two decades (2004-2023; R² = 0.55), during which time productivity increased despite persistent drought. Temporal modeling identified rising atmospheric CO2 concentrations as the strongest predictor of this shift, consistent with enhanced plant water-use efficiency under CO2 fertilization. Spatially, large agricultural valley floodplains act as anthropogenic refugia, sustaining productive mesic resources through flood irrigation and subsequent groundwater recharge into late summer. These findings suggest that human water management and physiological shifts in vegetation are currently buffering mesic systems against meteorological drought throughout U.S. rangelands.  However, this apparent buffering is spatially heterogeneous and may mask vulnerability to groundwater depletion, shifts in precipitation regimes, and woody encroachment. Sustaining these vital ecosystems will require local conservation approaches that go beyond climate monitoring to include balanced management considering both agricultural and ecological water needs and constraints.

Citation: Kristopher R. Mueller, Scott L. Morford, John S. Kimball, Joseph T. Smith, J. Patrick Donnelly, David E. Naugle, "Shifting resilience: Trends and predictors of mesic resource productivity in western U.S. rangelands," Ecological Indicators, Volume 190, 2026, 115334, ISSN 1470-160X

Acknowledgements: This research used compute and storage resources provided by Google Earth Engine. The US Bureau of Land Management of Montana/Dakotas provided funding for this research (grant code: F21AC00546) through the Intermountain West Joint Venture (IWJV) with help from the USDA-NRCS Working Lands for Wildlife.. 

Permanent URL: https://doi.org/10.1016/j.ecolind.2026.115334

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