Abstract
Privately owned rangelands in the western US support many ecosystem services and are threatened by financial incentives favoring conversion to housing development and more intensive forms of agriculture. Recognizing this threat, the impact investment community has identified rangeland management as a potential investing strategy to produce financial returns while preserving or enhancing the ecosystem services provided by intact rangelands. This strategy is based primarily on the notion that a capital-intensive conversion from continuous to rotational grazing can financially sustain rangelands through a combination of increased productivity and potentially monetized ecosystem service flows. The potential for these gains is supported by compelling anecdotal evidence, yet a robust body of scientific literature based on rigorous field experiments has not supported those claims, nor produced transferable estimates of the benefits provided by rotational grazing of livestock (particularly cattle in the western US). Therefore, to demonstrate investment viability and measure investment success, impact investors will likely need to address these well-documented disconnects through some combination of monitoring and process-based modeling. This study examines the extent to which existing modeling tools are up to this task, by assessing the ability of two process-based models to represent four specific rotational grazing benefits put forth by impact investors, using a ranch in northeastern Wyoming as a case study. Using the Soil Water Assessment Tool, we simulated high magnitude changes in the water balance from surface runoff to evapotranspiration, which may be a benefit or negative impact depending on context (Benefit 1). We simulated a decrease in soil water storage under rotational grazing, which directly contradicts the outcome assumed in investment literature (Benefit 2). Using the InVEST beta Rangeland Production Model (based on the Century ecosystem model), we simulated increased biomass productivity (Benefit 3) under rotational grazing, which enhanced animal performance under some management parameters but negatively impacted it in others (Benefit 4). We conclude that the impact investing community will likely find greater success through a shift to objective-oriented ranch management, rather than a specific focus on rotation, and will also need additional investment in science and monitoring to demonstrate benefits.
Highlights
Under a rotational grazing system surface runoff is approximately 572 ae-ft lower over the course of the year and ET is approximately 630 ae-ft higher over the course of the year for the entire Ucross property. These results indicate the potential for high magnitude changes, our model did not indicate that the forgone surface runoff corresponded with a simulated increase in percolation and recharge and by extension, the potential for increased on-farm water capture
Our Soil Water Assessment Tool (SWAT) model indicates that approximately 91% (572 ae-ft of 630 ae-ft) of the foregone surface runoff is evapotranspired under the rotational scenario; a tradeoff that is observed in the results presented in annual water balance ratio under baseline scenarios in Park et al (2017)
Because it is a model designed to be applied over large areas and with lightweight data requirements, RPM is limited in several ways that may obscure its representation of rotational grazing management
Summary
Rangelands comprise roughly 31% of the United States’ total land area with the majority of these rangelands located in the arid and semiarid western portion of the country (Havstad et al, 2007), where more than half are privately owned (Maczko et al, 2011) Many of these rangeland ecosystems are unique in that they can be managed for grazing and thereby simultaneously be kept in productive agriculture while maintaining native vegetation and soil cover, in contrast to other more intensive forms of cropping (Brown and MacLeod, 2011). Any negotiation of outcomes in that space needs to be underpinned by a solid understanding of the benefits (and potential negative impacts) associated with preserving functioning rangelands, so that they can be put on a more level playing field via financial or regulatory incentives (Havstad et al, 2007)
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