Monitoring The Multiple Benefits Of Regenerative Ranching

Rangelands are an essential part of the health and integrity of California landscapes. Regenerative rangeland management seeks to enhance the benefits and increase the ecosystem services these lands provide by improving the health and stability of soils, supporting and enhancing biodiversity, improving water quality and cycling, and helping achieve agricultural production goals.

Many of the principles underlying regenerative management have long been established by the scientific and agricultural communities. The practices that stem from these principles are a combination of ‘tried and true’ as well as less well documented practices. In our commitment to growing the evidence base for regenerative management in concert with increasing adoption, TomKat Ranch and Point Blue Conservation Science aim to discover, show proof of concept, and scale regenerative practices that help to grow the productivity and resilience of rangelands across California.

Since 2011, Point Blue Conservation Science has worked at TomKat Ranch conducting rigorous, transparent scientific research in order to help advance what is known about regenerative agriculture. Our work includes efforts to improve our understanding of how grazing strategies and other management practices can help to promote soil and ecosystem health through focus on a few basic principles.

To expand our learning, in 2014, we launched the Rangeland Monitoring Network (RMN), a program that now monitors ecological parameters on over 85 ranches in California. In this article, we share updates on the data collected at TomKat Ranch in the context of research on rangeland ecosystems and regenerative management across California.  Because soil carbon is central to soil health and thus the regenerative paradigm, we take a deep dive into the soil metrics. We also explore some of the critical co-benefits of regenerative ranching.

Soil Carbon

In the winter of 2014-15, we began monitoring soil carbon at 40 locations across TomKat Ranch. Baseline measurements showed soil carbon percentages varied from 2 to 10%.  Soil carbon measures were also taken at the other 85 ranches in the network, and TomKat Ranch, with an average value of 4% soil carbon, had among the highest carbon measures in the top 10 centimeters of soil.  In 2018, we conducted our first re-sampling of rangeland soils across the Network, returning to all of the locations tested three years earlier. During that three year time period (2015-18) and on the tail end of California’s mega drought, the Central Coast experienced moderately moist conditions briefly before returning to drought conditions (see TomKat Ranch’s Ranch Data Weather Webpage). With such an extended drought as this, we expected carbon inputs through photosynthesis to be less than carbon outputs via respiration, resulting in decreased soil carbon stocks during the time period. Unlike in more mesic climates that support ranches such as White Oak Pastures (a ranch that has reported remarkable rates of carbon sequestration), ranches in California’s semi-arid to arid climate, may find it hard to overcome these effects of drought even with regeneratively-focused management.

As expected, we saw a modest average decline in soil carbon from 0-10 cm depth across the monitoring network, including at TomKat Ranch. However, TomKat’s deeper soils (10-40 cm depth) did not decline significantly during that time period. We also observed that not all sampling locations in the network or on the ranch behaved the same way: in fact, 46% of the points monitored at TomKat Ranch gained soil carbon from either 0-10 cm, 10-40 cm, or both (see TomKat Ranch’s Ranch Data Soil Webpage). This shows that despite the overarching drought conditions during our sampling period, some soils actually gained carbon.

With these initial re-sampling data in hand, we are actively working towards understanding more about the points that gained and lost carbon and how management might enable conditions for carbon sequestration to occur in these and future locations. What are the factors that may determine whether, and to what degree, soil carbon sequestration is occurring at a given site? Here are a few primary ones:

• Quality and quantity of organic matter entering the system, which is a function of plant community composition and forage productivity
• Microbial physiology, especially carbon use efficiency (i.e., the fraction of carbon that is incorporated into microbial biomass versus respired as CO2)
• Soil texture and mineralogy, which affects how strongly organic matter is held onto mineral surfaces
• Soil aggregation, which physically protects carbon from being lost as CO2
• Topography and (micro)climate

Some of these factors like plant community composition can be influenced by management, while others like soil mineralogy can’t. As we continue to dig into the data, our hope is to disentangle these complex factors and determine what role management can play in promoting carbon sequestration across California’s rangelands.

Management Practices to Enhance Other Ecosystem Benefits

One of our goals for monitoring at TomKat Ranch and across the Network is helping producers achieve their management targets such as increasing perennial grass cover and vegetation diversity, and providing habitat for wildlife, including grassland birds. Here, we explore some of what we are learning through monitoring these co-benefits, and discuss our findings in the context of other studies.

Vegetation

California’s grasslands have been transformed over the last several hundred years. Once characterized by native perennial bunchgrasses and wildflowers, these landscapes today are dominated by introduced annual grasses which have contributed to an overall decline in the diversity of native species and systems. In order to achieve TomKat Ranch’s management goals of increasing perennial grass cover and plant species diversity, the Land and Livestock team controls the timing, intensity and duration of grazing to reduce the height and cover of often fast growing and vigorous annual grasses and give advantage to native bunchgrasses and wildflowers which often grow more slowly. By including periods of rest (from grazing disturbance) during the growing season, this allows the less competitive native plants an opportunity to grow and thrive.

When planned grazing began at TomKat Ranch, we found native perennial grasses in only 6 of the 74 fields. By 2013, presence of native perennial grasses had increased to 58 of 74 fields (Henneman et al. 2014). By 2018, we see native perennial grasses in 70 out of 74 fields.  It is possible these increases would have happened regardless of a change in management and our inference is limited by the lack of a control plot where we didn’t change management. Yet, these data suggest that management at least enabled the conditions for perennial grasses to recolonize much of the ranch.

Our observations at TomKat are supported by other studies that have found grazing benefitting native plant species richness and diversity.  For example, Areceo and colleagues (2017) found that grazing maintains native grasses and forbs in the presence of introduced plant species in Point Reyes National Seashore and Hayes and Holl (2003) found that grazed coastal prairies supported higher native annual-forb species richness than un-grazed coastal prairies. Similarly, Gennett et al. (2017) found native plant abundance to be higher in grazed areas. Taken together, these studies and others provide an evidence base for the theory that rangeland stewardship supports and enhances biodiversity.  By carefully managing the timing, duration, and intensity of grazing, it is possible to maximize the capacity of working landscapes to support the needs of diverse plants, healthy soils and the animals and microbiota that depend on them.

Birds

Across North America, grassland bird populations are declining rapidly (Brennan and Kuvlesky 2005).  While the reasons for this decline are not entirely clear, one thing is certain: healthy habitat is critically important for birds to thrive.  Grassland birds of California include Grasshopper Sparrows, Savannah Sparrows, Burrowing Owls, and Horned Larks. TomKat Ranch supports a diverse community of native songbirds, including a high density of Grasshopper Sparrows exceeding population targets set by California Partners in Flight and the Central Valley Joint Venture (Preston et al. in prep).  In addition, at TomKat Ranch and across the Rangeland Monitoring Network, our data support other studies (DiGaudio 2010, Gennet et al 2017) demonstrating the value of rangeland landscapes for grassland birds. Managing grazing for grassland birds includes using animal impact to maintain the structure and composition of the plant community that is most suitable for the bird species of interest, and also timing grazing to minimize disturbance to high density nesting areas during the breeding season.  By carefully monitoring grassland bird population across the ranch, with particular focus on breeding habitats, we can inform grazing management to best serve these sensitive species.

Conclusion

Point Blue Conservation Science and TomKat Ranch are committed to being a part of a community of practice that works to advance the evidence base for regenerative management. Our work focuses on California’s rangelands which support, and are supported by, a three billion dollar cattle industry. These lands are especially critical for providing habitat for wildlife and native plants, and in achieving the state’s climate mitigation goals (Cameron et al. 2017; Sleeter et al. 2019).  Together we work across a spectrum of research and development, from testing new methods to refining and advancing established practices, in order to enhance the ecosystem services that natural and working lands provide. We find hope in the potential of regenerative agriculture to serve as a focal point in a solution set that may address many of the challenges facing the world today. Whether that challenge is climate change, biodiversity loss, flood, drought, or food insecurity, regenerative agriculture may be an opportunity to simultaneously benefit both people and the planet.

Literature Cited

Arceo, M., R. Content-Castro, J. Jougla, L. Teague (2017) Ecological role of cattle at Point Reyes National Seashore: effects of grazing history on coastal plant communities. California Ecology and Conservation Research.  https://doi.org/10.21973/N3WW8C

Brennan LA, Kuvlesky WP Jr. North American grassland birds: An unfolding conservation crisis?. Journal of Wildlife Management. 2005;69(1):1–13.  https://doi.org/10.2193/0022-541X(2005)069<0001:NAGBAU>2.0.CO;2

Cameron, D.R., D.C. Marvin, J.M Remucal, M.C. Passero (2017). Land-based activities for climate mitigation. Proceedings of the National Academy of Sciences114: 12833-12838. https://doi.org/10.1073/pnas.1707811114

DiGaudio, R. T. (2010) Grassland bird monitoring at the Jenner Headlands: A report of the 2010 field season. PRBO Conservation Science report to the Sonoma Land Trust. https://www.prbo.org/refs/files/12100_RyanDiGaudio2010.pdf

Gennet, S., E. Spotswood, M. Hammond, J.W. Bartolome (2017). Livestock grazing supports native plants and songbirds in a California annual grassland. PloS one 12: e0176367. https://doi.org/10.1073/pnas.1707811114

Hayes G. F., K. D. Holl (2003) Cattle grazing impacts on annual forms and vegetation composition of mesic grasslands in California. Conservation Biology 17:1694-1702. https://doi.org/10.1111/j.1523-1739.2003.00281.x

Henneman, C., N. E. Seavy, and T. Gardali (2014) Restoring native perennial grasses by changing grazing practices in central coastal California. Ecological Restoration 32:352-354. https://doi.org/10.3368/er.32.4.352

Preston, M., R. DiGaudion, H. Allen, B. Eyestone, A. Fogg, E. Porzig.  In prep. Grassland and Oak Woodland focal bird species richness and abundance across California rangelands.

Sleeter, B.M., D.C. Marvin, D.R. Cameron, P.C.Selmants, A.L. Westerling, J. Kreitler, C.J. Daniel, J. Liu, T.S. Wilson (2019) Effects of 21st‐century climate, land use, and disturbances on ecosystem carbon balance in California.  Global Change Biology 25:3334–3353. https://doi.org/10.1111/gcb.14677