By John M. Eadie, Daniel S. Karp, and Andrew L. Rypel

Picture a farm. Only one crop type is grown over a vast field stretching to the horizon. Signs of modern agriculture are everywhere— tractors slowly driving by, fields engineered in neat squares, with millions of precisely spaced plants. All cues indicate much food will be harvested from this modern, industrialized farm. But you probably do not expect to see wildlife. Neither do most conservation biologists. Indeed, farming is a main cause of the global biodiversity crisis, largely because it has intensified and expanded to cover more than 40% of Earth’s land surface. In California’s Central Valley, farming has drained >90% of our wetlands and replaced them with farms. 

Recognizing this, many conservation practitioners have spent several decades exploring how to mitigate agriculture’s impact on wildlife. We now know that many species can persist in farmland, sometimes even as many as in nearby natural habitats. That is, provided farmers implement practices that support ecological benefits. These practices might include growing multiple crop types, fertilizing with composts, planting hedgerows or flower strips, and maintaining patches of nearby natural habitat. Yet while such practices often abound in small-scale, diversified farms, scaling up to create wildlife-friendly, industrial-scale agriculture remains a challenge. 

Rice is perhaps the clearest exception. Rice is a semi-aquatic crop, meaning water must be shared across farms and large landscapes to facilitate agriculture at scale, especially in semi-arid regions like California. The historical success of rice agriculture in the California’s Central Valley is clear. The Valley has upwards of 500,000 acres of rice fields, and most varieties grown are considered high quality. Nearly all sushi rice in the USA comes from California’s Central Valley (Calrice). Importantly though, rice fields also mimic the ecological conditions of historic wetlands that once dominated the Valley, meaning rice can support diverse populations of wild aquatic and semi-aquatic organisms. The rise of awareness on this topic has somewhat idiosyncratic origins.

Following harvest, rice farmers must eliminate waste rice straw, and until recently, the straw was burned in the fields each fall. Due to air quality and health hazards, state legislation in 1991 severely restricted rice straw burning. So, farmers began flooding fields after harvest in winter to decompose the straw. As the practice took hold, so too did California’s biodiversity. Millions of waterfowl began visiting rice fields, using them as surrogate wetlands. Shorebirds and cranes also began foraging and roosting in these fields in great numbers during the winter. Now, >200 species use California rice lands for essential parts of their lifecycles. Biologists have shown that flooded fields are highly productive rearing habitat for California’s threatened fish fauna, including Chinook salmon. The incredible story is not just limited to the winter. At-risk species like giant gartnersnakes and black terns now depend on fields filled to the brim with rice plants in the summer. 

But this success story is under threat. Droughts, shifting economies, and increased water prices cause many growers to stop flooding their fields in winter or abandon rice growing entirely. The number of fallowed rice fields tripled in recent drought years. Looking forward, how can we manage rice for conservation while still growing rice, recognizing that California’s vast natural wetlands will simply not return to its pre-development scale? 

Late in 2024, the California Rice Commission reached out to scientists at UC Davis and Point Blue Conservation Sciences and posed this deceptively simple, but deviously complex question. Assuming that we maintain the current level of natural habitats, would it be possible to collectively estimate the number of acres of rice needed to meet many of the conservation needs of multiple species?  The last part of this question was the kicker – it was not just one species that we were asked to consider but multiple – giant gartersnakes, non-breeding waterfowl, breeding and non-breeding  shorebirds, sandhill cranes, and fishes, notably salmon.

With a team of eight principal investigators, two postdoctoral fellows, and two PhD students, each with long histories of working with these species and expertise in rice agronomics and economics, we took on this challenge. Yet despite the talent pool, several of us doubted seriously whether we could do this, certainly not in less than one year. But we did. What, specifically, did we do?  In some ways there’s absolutely nothing new in the report … and in other ways, there is much that is new. 

What isn’t new?  For the five species groups considered, we already know a lot, and indeed, that’s why we chose them as focal groups for this analysis. These are all species of conservation management concern, all depend on rice fields for some or all their annual needs, and we had extensive background information on their life histories and conservation needs.

We have also learned much about the conservation value of rice over the last 30 plus years. In the report, we summarize this research, especially on the conservation value of winter-flooded rice fields (see Table 1). We have learned much over recent decades. 

So, what is new? This is the first time multiple key species have been considered together in one synthetic analysis. Most of the 60 studies in Table 1 focus on only one or a few species, or a few rice management practices. There have been few attempts for any agricultural crop in California to evaluate the conservation value for multiple species simultaneously in one comprehensive analysis (but see Suddeth and Lund 2016 for an excellent example). This is much more challenging, requiring a synthesis of the ecological, agronomic, economic, and management influences on multiple taxonomic groups as well as a synthetic evaluation of potential mutual benefits or tradeoffs. Our analysis charted a new path to evaluate multi-species conservation at a landscape scale for a major industrial-scale agricultural commodity. 

We did this to move beyond ‘old-school’ single-species management thinking – what we might call ‘postage stamp conservation’: well-meant conservation plans that focus on a few species in a focal area. Single-species thinking leads us to ‘us-versus-them’ discussions … fish vs. fowl, shorebirds vs. ducks, hatcheries as the sole answer for fish, farmers vs. wildlife.  We must move beyond this mindset.

We need to embrace systems-thinking. Doing so, enables management at the scale where multiple species interact with the landscape, with other species, and with us. In this project we considered the entire California Rice ecosystem. And we ask – what can we do to: (a) provide benefits for as many species as possible on rice fields in the valley, (b) limit negative impacts on any single species, and (c) enable us to evaluate mutual opportunities or potential tradeoffs in our management and conservation decisions?

We brought together experts from UC Davis and Point Blue Conservation Science to address three key questions that emerged from the California Rice Commission:

1. How many rice acres do we need to provide benefits for multiple species?
2. What rice management practices are most beneficial for each group of species and what practices are not or may impose constraints on some species? (Spoiler alert – the key is water availability and winter-flooding).
3. Finally, where in the valley might rice acreage be of high conservation value to the greatest number of species? Are there some areas with opportunities to benefit multiple species simultaneously, or areas where tradeoffs need to be considered.

We took a multifaceted approach.  We first developed a single baseline mapping framework including multiple habitat components that could influence the abundance and distribution of various wildlife species. We then reviewed the core needs of the five key species groups with respect to ricelands. With this information, we estimated the rice acreage, management actions, and locations that would be of greatest value to each species group. Finally, we synthesized key outcomes from our taxa-specific analyses to evaluate the rice footprint needed to support these species groups. Many of our analyses were new, using novel approaches, and the background research was extensive totaling 173 pages.

How big is the rice conservation footprint and what does it include? Our estimates of the planted rice acreage needed to help meet conservation goals for these taxonomic groups, assuming current levels of other habitat, include: 30,000 ac for native fishes (only Yolo and Sutter bypasses were considered), 43,139 ac for sandhill cranes, 80,000 ac for giant gartersnakes, 373,540 ac of winter-flooded rice and flooded fallow rice fields for non-breeding shorebirds, 472,794 ac of planted rice to restore populations of black terns and support other breeding shore birds, and 500,000 ac for non-breeding ducks. We suggested that a minimum rice footprint could be determined as that which satisfies the minimum needs of the species with the largest acreage requirement – any reduction of rice below that target would impact at least that one species, if it weren’t made up by increasing habitat in other ways. Under this premise, a minimum footprint of ~470,000– 500,000 acres would define the conservation footprint. 

Importantly, ricelands are not the only areas needed to support these species. As noted, our analysis assumed that current acres of natural and managed wetlands, uplands, and other critical habitats would be maintained at contemporary levels (see also below). If these areas declined, then many of the wildlife populations analyzed here could be in serious jeopardy. If, conversely, natural wetlands and other critical habitats were dramatically expanded, then less rice would be needed. Ultimately, however, it is extremely unlikely that the vast wetlands that typified the Central Valley more than a century ago are coming back. Furthermore, in some cases (e.g., salmon), our analyses clearly show that the current geographical footprint of rice alone is insufficient to meet conservation goals. Thus, a holistic approach to conservation, where rice serves as one critical piece of a larger strategy will always be superior.

Our mapping analysis helped identify rice locations of high priority for several species (Figure 2). For nearly all wildlife groups, the Colusa and Sutter basins are the highest priority locations for rice habitat, given their proximity to wetlands and wildlife refuges. The Yolo Basin, Consumnes-Mokelumne Rivers region, and parts of the Delta are especially important for shorebirds and sandhill cranes. The Yolo and Sutter bypasses also are critical areas for fish in flooded rice fields. Nonetheless, we emphasize that (1) these are not the only areas of conservation importance, (2) they are not weighted rankings of conservation value, and (3) they do not define the minimum footprint. Rather, these priority maps will be most useful in strategic conservation planning to identify focal areas where joint management may be most effective and/or where management tradeoffs for different species may occur.

In addition to addressing our three central questions, we also reviewed current agronomic practices and assessed potential changes to rice acreage in the valley; we evaluated the potential economic value to the public from the conservation value of rice; we identified research needs for each species group; and we described steps to develop a more refined rice conservation footprint.

This was a first attempt at this landscape scale … an initial footprint for guidance on: how much, how managed, and where in the valley can rice provided the greatest conservation value.

It is a “muddy” footprint and there is much more to do. We need to expand our consideration and analyses of the footprint for fishes and for other species for which data are emerging.  For example, we lacked data or mapping to incorporate “fish food” production initiatives in rice fields and floodplains beyond the bypasses.  Likewise, we lacked the data layers needed to include breeding waterfowl. Wading birds, raptors, passerine birds, mammals (e.g. bats), amphibians, and invertebrates (notably aquatic insects) all use ricelands and we need to consider the conservation value to those species. Post-harvest straw management practices are changing, and we critically need to consider future risks of reduced winter flooding and limited water availability. Water is the overarching key though – 500,000 acres of dry rice in the winter provides little conservation value for most wildlife. 

And we need to consider rice in the context of the entire Central Valley ecosystem. Adjacent wetland and upland habitats are essential for many of the species we considered and must be incorporated into an expanded valley-wide footprint.  The conservation value of one depends on the other. If we lose more wetlands, the conservation footprint for rice needs to be larger (and vice versa), or both systems will fail to meet conservation objectives.

Finally, this report shows we now have the quantitative tools for more sophisticated analyses such as multi-purpose optimization and multi-objective decision analyses. These analyses require detailed quantitative data on the conservation values of rice to each species group, the logistic constraints, and the economic tradeoffs of alternative management and conservation decisions. Nonetheless, we believe our initial footprint, muddy though it may be,  provides a solid foundation and a new framework by which to take those next steps –  to refine that footprint  and ensure the conservation value of California rice for the wildlife into the future.

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John M. Eadie is a University Distinguished Professor Emeritus and the D. G. Raveling Chair of Waterfowl Biology Emeritus in the Department of Wildlife, Fish & Conservation Biology at University of California, Davis. He is also a faculty affiliate at the Center for Watershed Sciences. Daniel S. Karp is an Associate Professor in the Department of Wildlife, Fish, and Conservation Biology at University of California, Davis. Andrew L. Rypel is a Professor and the Peter B. Moyle and California Trout Chair of coldwater fish ecology at the University of California, Davis. He is a faculty member in the Department of Wildlife, Fish & Conservation Biology and past Director of the Center for Watershed Sciences.

Further Reading:

A summary of the report can be found here: 
 https://calrice.org/wp-content/uploads/2025/02/CRC_Rice-Footprint-Summary_2025_v5.0.pdf

A  copy of the full report can be found here:
 https://watershed.ucdavis.edu/resources/5796

Helping fins and feathers podcast:  https://podcast.calrice.org/episode-29-helping-fins-and-feathers/

Eadie, J.M., Karp, D.S., Bellido-Leiva, F., Burrows, L.R., Dybala, K.E. Fogenburg, S.P., Linquist, B.A., Rypel, A.L., Sumner, D.A. Todd, B.D., Walsh, R.G. Xu, J. 2025. A Conservation Footprint for California Rice. Report to the California Rice Commission. University of California, Davis, and Point Blue Conservation Science. 173 pages.

Golet, G. H., K. E. Dybala, M. E. Reiter, K. A. Sesser, M. Reynolds, and R. Kelsey. 2022. Shorebird food energy shortfalls and the effectiveness of habitat incentive programs in record wet, dry, and warm years. Ecological Monographs 92:e1541.

Kremen, C., and A. M. Merenlender. 2018. Landscapes that work for biodiversity and people. Science 362:eaau6020.

Mount, J., A.L. Rypel, and C. Jeffres. 2023. Nature’s gift to nature in early winter storms. https://californiawaterblog.com/2023/01/15/natures-gift-to-nature-in-early-winter-storms/

Moyle, P., J. Opperman, A. Manfree, E. Larson, and J. Florsheim. 2017. Floodplains in California’s future. https://californiawaterblog.com/2017/09/10/floodplains-in-californias-future/

Petrie, M. J., and K. L. Petrik. 2010. Assessing waterbird benefits from water use in California ricelands. Ducks Unlimited. Report to the California Rice Commission. https://calrice.org/pdf/DucksUnlimited.pdf

Petrie, M. J., M. Brasher, and D. James, Estimating the biological and economic contributions that rice habitats make in support of North American waterfowl. The Rice Foundation, Stuttgart, Arkansas, USA. https://www.usarice.com/docs/default-source/the-rice-foundation/research/estimating_the_biological_and_economic_contributions_that_rice_habitats_make.pdf?sfvrsn=5eadde8d_2

Rypel, A.L., D.J. Alcott, P. Buttner, A. Wampler, J. Colby, P. Saffarinia. N. Fangue, and C.A. Jeffres. 2022. Rice and salmon, what a match! https://californiawaterblog.com/2022/02/13/rice-salmon-what-a-match/

Strum, K. M., M. E. Reiter, C. A. Hartman, M. N. Iglecia, T. R. Kelsey, and C. M. Hickey. 2013. Winter management of California’s rice fields to maximize waterbird habitat and minimize water use. Agriculture, Ecosystems & Environment 179:116–124

Suddeth, R., and J. Lund. 2016. Multi-Purpose Optimization for Reconciliation Ecology on an Engineered Floodplain–Yolo Bypass, California, USA. San Francisco Estuary and Watershed Science 14. https://doi.org/10.15447/sfews.2016v14iss1art5

Torres, F., M. Tilcock, A. Chu, and S. Yarnell. Five “F”unctions of the Central Valley floodplain. https://californiawaterblog.com/2022/05/08/five-functions-of-the-central-valley-floodplain/