Could “lost crops” help us adapt to climate change?

Archaeology might not solve all the agricultural challenges that climate change will bring, but it could provide important lessons and a record of new ideas.

Today, our food sources are streamlined: Around 90% of the world’s calories come from about 20 species of plants. Nearly 50% of calories come from rice, maize, and wheat alone. Climate change is pushing these crops to their limits. An Intergovernmental Panel on Climate Change report on food security indicated that crops in many regions already have a tough time coping with extreme temperatures, shifting rain patterns, and elevated carbon dioxide levels.

A recent study published in Nature Food used new crop modeling tools to project the effects of climate change on major crops worldwide. The models projected that wheat productivity would increase in high-latitude parts of the world. However, maize, soybean, and rice yields will take a hit in the next 10 to 20 years. Agriculture in the hottest, driest, most arid, and generally lower-latitude places on Earth will be hit by the effects of climate change soonest.

“Changes are around the corner, they’re substantial, and adaptation needs to be planned out in a systematic way,” said lead author Jonas Jägermeyr, a climate change scientist at Columbia University and the NASA Goddard Institute for Space Studies.

Commonly discussed agricultural adaptation strategies include planting different crops, breeding new lines, genetically modifying crops to make more drought- and heat-tolerant varieties, and shifting growing seasons to accommodate shifts in rainy seasons and temperatures. Strategies may also incorporate more sustainable agricultural methods to help protect the ecosystem, maintain soil fertility and moisture, and contribute less to greenhouse gas emissions.

Put simply, adaptations essentially boil down to tinkering with what we plant, where we plant it, when we plant it, and how we tend to it. We can see these adaptations play out over and over again in the archaeological record.

A long, hard look at the past

Could the archaeological record help provide new perspectives on agricultural resilience, crop diversity, and sustainability in the face of climate change? Archaeologists studying past agricultural practices are looking for lessons on how people have bolstered their food systems against past instances of climate change. They are also exploring the cultivation of ancient crops—the enduring veterans of past climate challenges—as resilient options to diversify our food sources.

John M. Marston, an archaeologist from Boston University, said that early archaeologists studying agriculture focused on what people were growing and how it changed over time. That focus has evolved: “Over the last several decades, people have been much more interested in why things changed over time,” he said.

Archaeologists strive to understand past civilizations within the context of their climates. However, agricultural change can be related to economic, political, cultural, and environmental factors. The current conflict in Ukraine, for instance, is largely unrelated to climate change but will have far-reaching consequences for the world’s food supply: In addition to Ukraine being “Europe’s breadbasket,” Ukrainian crops dominate wheat imports from Egypt to Indonesia. The United Nations warned global food costs could surge another 22% as war stifles trade and slashes future harvests.

“Disentangling the social and the environmental component is a real challenge,” Marston said.

To unravel the changes in food production over time, archaeologists employ various tools. Charred plants and seeds, garden plots, and farming infrastructure can be clues to agricultural practices. Methods such as radiocarbon dating can estimate artifacts’ ages, and paleoclimatic proxies can reveal details of past climates.

Paleoclimatic records are incomplete in many regions around the world; southwestern China is one exception. In a 2018 study in Science Advances, researchers combined weather station data, paleoclimate records, and archaeological data of seeds to model the impact of climate change on Asian agriculture.

They found that global cooling around 3,700 to 3,000 years ago caused the common crops of the time—broomcorn and foxtail millet—to fail. Ancient farmers switched to more cold-tolerant crops like wheat and barley and invested in trade to move food to different areas.

Archaeologists are also investigating paleoclimate records in Central America, where Maya farmers experienced two periods of extreme social and environmental stress. Before the infamous collapse of the civilization around 800–1000 CE, a smaller transformation occurred around 100–250 CE. Although the reasons for both of these events are complicated, Chelsea Fisher, an archaeologist with Washington and Lee University in Virginia, said, “Climate change was a part of it, environmental degradation was a part of it, and political instability was a part of it. Those would have been in a positive feedback loop.”

Fisher and her colleagues excavated the houses and gardens of rural farmers dating to before 250 CE in the rural hinterlands near the ancient city of Yaxuná in Mexico. Fisher and her team found that farmers were intensively farming the areas around their homes. But when the social and environmental turmoil hit, they abandoned the land around 250 CE. A couple of centuries later, as Maya farmers returned to this land, they employed more mobile and flexible farming strategies, like the agricultural practice called milpa, which is still used in the region today. Milpa involves burning wild vegetation to clear a plot of land, cultivating it for a year or two, and then moving to a new plot.

When the second, more devastating disruption of the Maya empire occurred, the mobile farmers were more resilient. Fisher said these farmers fared so much better the second time around because they were more flexible with their agricultural practices.

The pandemic has made it challenging for Fisher to continue her archaeological work on traditional agricultural practices in Yaxuná, but she hopes to return this summer. In the past, Fisher and her team worked with local authorities to hold regular public meetings so that she could collaborate with community members on what questions the archaeological work should address. For instance, many community members expressed an interest in learning about a colonial era ranching hacienda that tied the region into the global food system and industrial agriculture.

When Fisher returns to Mexico, she plans to work with community members to excavate the hacienda and investigate how colonial powers attempted to constrain Maya traditional ecological knowledge and how the Maya resisted authorities to practice and pass down that knowledge, which endures today. “The first step will be just establishing ties again with the community, because any sort of meaningful partnership depends on community engagement and trust,” she said.

Traditional Hawaiian agriculture offers another exceptional example of how to deal with climate changes. Indigenous Hawaiians sustained a higher population before European arrival than they do today, relying entirely on local resources. Hawaiians successfully maintained this population level through incredibly diverse agricultural practices that made use of local ecosystems.

For instance, Kohala, the area on the northwest tip of the Big Island of Hawaii, has radically different ecosystems and has different agricultural practices suited to each one. Its coast is dry, and the soil is fertile. As one moves inland and uphill from the coast, rain is more common, and the soil is wetter but less fertile. In the low-lying dry regions, Native Hawaiians planted crops when rain allowed and placed stone mounds to shade the soil and allow it to better retain moisture. These dryland crops were primarily grown for reasons other than food, such as pili grass used for thatching. Moving upslope slightly, farmers employed agroforestry, dominated by breadfruit. Above that, where both rain and soil fertility were best, they planted staple crops like taro, and higher still, where soil fertility was low, they employed more agroforestry. Goldilocks wouldn’t have found anything too hot or too cold in Kohala.

The variations in agricultural practices allowed for more farmable land and a greater diversity of resources, which Noa Kekuewa Lincoln, a soil scientist at the University of Hawai‘i at Mānoa, said allowed Hawaiians to successfully weather climate changes. He added that these ancient practices can also teach us how to handle climate change today: “By looking at how they adapted their practices along these ecological gradients, I think is a really strong parallel to the type of adaptation that would happen under a warming or a drying climate regime.”

Fisher, too, said flexibility is a theme she’s noticed throughout history. “The overriding message that I see coming through in archaeological case studies is the importance of flexibility and the avoidance of rigidity traps,” she said. “And I think we’re living through a similar moment in time that civilizations have gone through before.”

Digging for diversification strategies

In addition to highlighting the successes and failures of past civilizations, archaeology can also reveal crops and agricultural practices that might be resilient to the current period of climate change. In many locations around the world, certain crops are still grown but have become what Philippa Ryan, an archaeologist with the Royal Botanic Gardens, Kew, calls minor crops.

“Archaeology provides a backstory to today’s minor crops,” she said. They’re likely to be resistant to pests and don’t require fertilizers. In many cases, these plants are extremely drought and heat tolerant. The millets that Chinese farmers were growing nearly 4,000 years ago, for instance, and plants such as teff and amaranth are naturally heat and drought tolerant, as well as nutritious and fast growing. Some varieties of these cereals are still cultivated, but not as widely as wheat or rice.

Ryan and her colleague Mohamed Saad from the National Corporation for Antiquities and Museums in Sudan think that climate change may make it a better investment for farmers to grow minor crops more often. Saad said that faced with climate change and economic challenges surrounding imports, “the farmers may try to go back and grow them.”

In Sudan, Ryan and Saad have linked the archaeological record with the present day through interviews with elderly farmers who grew up with crops (such as hulled barley, sorghum, and pulses like lablab and lupin) that have since fallen by the wayside, replaced mainly by bread wheat and broad beans. These farmers provide key knowledge about past practices and crop uses. For example, farmers explained how land and crops were chosen for natural irrigation and how these methods have changed because of water pumps, dam systems, and other contemporary farming methods.

Like traditional ecological knowledge, archaeology employs a holistic approach, Ryan said, so in addition to the agricultural usage of plants, she looks at their cultural significance. In many cases, plants become part of the “biocultural heritage,” taking on great significance when their lengthy histories are known. “Agricultural heritage is cultural heritage,” she said.

In Kenya, traditional vegetables, including cultivated and wild species of cowpeas and mallow, have been listed as U.N. Educational, Scientific and Cultural Organization (UNESCO) cultural heritage. The leafy greens are recognized for their “ability to improve nutrition and sustain smallholder farmers’ livelihoods.” “That’s a good example of where the resilience meets the culture,” said Ryan.

Marston said the archaeological record holds clues to diversifying more than just human food. He mentioned a legume called bitter vetch, which people in west Asia appear to have domesticated around 11,000 years ago and is similar to barley. “The two of them were often grown together in the past as fodder for animals,” he said. “Today, they don’t grow it as much, but potentially, it is a more arid-adapted, dryland-adapted crop that could be used for that.” Compared to other legumes, Marston said, “if you want something that has a good protein content, it is one of the lowest water-requiring crops there is.”

Lost crops

Some foods are no longer cultivated at all and have been identified only through archaeological research; these lost crops may also provide helpful clues about resilience and adaptation.

“[Archaeologists] study climate change whether we do it explicitly or not,” said Stephen Carmody, an assistant professor at Troy University in Alabama. “To study the past, you’re asking questions about how society changed and cultural phenomena. A lot of times, you can’t separate those from past climates.”

On the Cumberland Plateau in Tennessee, Carmody is collecting data to examine how the environment might have affected agricultural practices. Years ago, he helped excavate two ancient cave shelters on the plateau that had been occupied as far back as 10,000 years ago. Around 3,000 years ago, both shelters were occupied at the same time, yet their contents were drastically different. In one cave, on the top of the plateau, Carmody found mostly remains of fruits and nuts, but no seeds. The other cave was located on the plateau’s slopes, less than 3 kilometers from the first, and inside he found wild bean seeds and domesticated seeds of maygrass and one subspecies of goosefoot. He’s currently in the process of analyzing samples from other shelters to see if they show the same pattern of hillside agriculture.

Carmody has already experimentally cultivated several lost crops species such as goosefoot, sumpweed, little barley, and maygrass, but if the patterns from the cave excavations hold up, Carmody said it would be worth trying to grow them under the same conditions on the hillsides. Plus, the lost crops were grown together on the same plot of land over multiple growing seasons as a polyculture system. He said the way Indigenous Peoples farmed on the Cumberland Plateau could be completely different from how we think of agriculture today and could teach us new ways to diversify the land and crops we use.

Since the lost crops were replaced largely by maize between 300 BCE and 1 CE in North America, the agricultural knowledge of how to grow them has also been lost, and many other plants now take precedence as culturally significant plants for Indigenous communities. David Anderson, a horticultural operations specialist with the Eastern Band of Cherokee Indians, runs a greenhouse and seed bank dedicated to cultivating and preserving an exhaustive list of plants with cultural ties to the tribe today. He said he selects what he produces at the greenhouse on the basis of the needs of the community.

“You could argue that every native plant that’s here is of cultural significance. But I try to focus on those things that people are noticing that there’s a lack of,” Anderson said. Although he doesn’t grow any of the lost crops, Anderson sees the value in reintroducing edible native plants of all kinds to increase biodiversity and resilience. “Maybe one day [these plants] are resilient to climate change, and we can rely on them,” he said.

Who wants sumpweed for dinner?

For Anderson, getting edible plants back into the landscape is “a goal, of a goal, of a goal.” And Carmody is unsure whether lost crops could ever again become major food sources because of both economic drivers and taste preferences. “If I put sumpweed in front of my kids, they probably won’t eat it,” he said.

Billions of people have adapted to certain expectations of what’s produced by our modern food system, Jägermeyr said. “You’re not going to change these overnight.”

Another issue in introducing lost crops is the fact that they sometimes involve outdated technology, said anthropologist Lynn Swartley O’Brien, an assistant professor of anthropology at Montgomery County Community College in Pennsylvania. For example, she said, raised-field agricultural techniques were identified by archaeologists in Bolivia in the 1980s. These techniques, although site specific and sustainable, were remnants of Indigenous cultural heritage that in the 20th century, were extremely labor-intensive for farmers working within the confines of colonialism. Such Indigenous Knowledge couldn’t be reasonably replicated.

Scaling production of lost or Indigenous crops also introduces economic, ecological, and social complexity in the region to which the crops are native. Bolivia experienced radical price fluxes and soil degradation in the 2000s, for example, as a result of the increased consumption of quinoa in the Global North.

The power of traditional ecological knowledge

Rather than rely on Western academics identifying lost crops and cultivation techniques, Fisher said climate-focused archaeologists should look for “ways to support traditional and Indigenous farming communities that are [already] practicing ancient techniques and to support them in continuing to do what they’re doing.”

Michael Kotutwa Johnson, a traditional dryland farmer and Hopi tribal member with a Ph.D. in natural resources and conservation, said that many traditional agricultural systems have perished because of industrialization, but ancient practices still exist.

“We’ve been farming out here for 3,000 years. So we’ve experienced environmental fluctuations,” said Johnson. He said that the Hopi techniques he uses to farm in northern Arizona without irrigation are specifically designed to help with those fluctuations. For example, in the springtime, Johnson looks at naturally growing plants to determine how deep and spaced out he needs to plant his corn to get a good harvest. “What we do is very resilient. And what we do is science based in our own way.”

Johnson grows squash, melons, beans, and 21 varieties of corn, and he used to grow Hopi cotton. He said that the archaeological record reveals the long, persisting histories of these plants but that scientists don’t always consult with Indigenous Knowledge Holders and end up duplicating work that is known in the Indigenous community. “Archaeologists sometimes don’t ask us what things are for, so they just wind up proving something we already know about,” he said, laughing.

In Hawaii, the nonprofit Ulu Mau Puanui is dedicated to research and education on ancient agricultural practices. Hawaii imports nearly 90% of its food, and Ulu Mau Puanui hopes that the revival of traditional agricultural practices will help increase food security.

“There is a big movement for the revival of Indigenous and traditional agroecological systems to try to better understand and bring forward adaptive practices that allowed our ancestors to not only survive but thrive in these landscapes for centuries,” Lincoln said.

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