When you think of Rapa Nui,  also known as Easter Island, the first thing that comes to mind is  probably the giant stone statues called moai.

But carving massive human faces  isn’t the only creative way the Rapa Nui people brought rocks to life. They also used millions of ordinary,  non-face-having rocks to sustainably grow food on their barren little  island – for hundreds of years.

In fact, these islanders have a lot to  teach us about resilience in the face of today’s environmental challenges. And how you can turn rocks into food. Sort of. [♪ INTRO] Rapa Nui is a tiny, isolated  island in the Pacific Ocean, 3,800 kilometers west of South America.

The first human inhabitants arrived from other Polynesian islands around the year 1200 CE. At first, the island was covered in palm trees. But then the humans got to  work cutting some of them down, and the rats that had hitched a boat  ride feasted on the saplings and nuts.

Within a couple hundred years,  almost all the trees were gone. Without the trees’ protection, strong  winds eroded the soil and dried it out. Rainfall was unpredictable, and when it did rain, the soil drained quickly  rather than retaining moisture.

The island has very little fresh water,  so irrigation wasn’t really an option. And to cap it all off, the soil  was relatively poor in nutrients. In fact, you might have heard this as a  cautionary tale about ecological destruction.

According to this debunked and  frankly insulting, narrative, the population of Rapa Nui grew dramatically  during the period of deforestation and then crashed because they were “too greedy” to use the island’s resources responsibly. And, sure, the deck was  kinda stacked against them. But human ingenuity came to the rescue.

The archaeological evidence actually  shows that the Rapa Nui people were able to sustain a  small and stable population, probably around 3,000 to 4,000  people, for a long period of time. They did this thanks in part to a set of agricultural techniques called rock gardening. Rock gardening is pretty much what it sounds like: putting rocks in gardens or agricultural fields.

Rapa Nui is volcanic and has  many outcroppings of basalt, so people would break off  rocks from these outcroppings and carry them to their  gardens about 65 meters away. When life gives you rocks, make… rock-ade? They constructed three types of rock gardens.

For veneer gardening, they placed a layer  of fist-sized rocks directly on the ground. Lithic mulching involved adding  broken rocks to the soil, from the surface down to about 20 centimeters. The last type was boulder gardens, where they simply placed  large stones on the ground.

In some gardens, as much as 80% of  the surface was covered by rocks. Now, this still doesn’t sound terribly useful. If the fields are full of rocks,  where are all the vegetables?

But trust me – this actually works. Rock gardening offers a bunch of  benefits that enabled the Rapa Nui to grow tubers like sweet potatoes. Remember how dry the soil was?

Well, rock gardening decreases evaporation, allows more precipitation to filter into  the soil, and decreases water runoff. Studies done elsewhere suggest  that over a two-year period, soil with rock mulching can store 30 to  40% more water than the bare soil does. The rocks took care of the runaway wind, too.

By creating a rough landscape,  rock gardening slows down the wind and reduces soil erosion by at least  four times compared to non-mulched land. Rock gardening also puts  the kibosh on pesky weeds. And as the weather gradually breaks  off tiny fragments of basalt, the soil gains some nutrients, like calcium.

All this leads to more seeds  successfully sprouting, heftier plants with deeper  roots, and higher crop yields. We don’t know how big the benefit  was for sweet potatoes on Rapa Nui. But in later experiments,  the yield of maize in a rock mulched field was up to 4 times  the yield in a non-mulched field.

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The Rapa Nui weren’t the only  civilization to realize that humble rocks could work  wonders for food production. We don’t know how widespread  rock gardens used to be, since Western archaeologists  have often overlooked them or misinterpreted their purpose. But evidence of historical rock gardening  has been found all over the world.

For example, the Hohokam people  in present-day southern Arizona built thousands of rock mounds to  cultivate agave during droughts. And more than 2,000 years ago, the  Nabatean people in the Negev Desert in the Middle East grew olives,  pomegranates, and apples on rock terraces. Now, it’s not like you can just  throw some rocks in your garden and expect a bountiful harvest year after year.

Rock gardening decreases the  organic content of soil by up to 10% after just one year, and it’s not  exactly easy to mix organic matter back into the soil that’s covered with rocks. As a result, the practice could deplete  some soil nutrients over a few decades. A saying among Chinese farmers using  rock gardening in the early 20th century was “The father works hard, the son gets  rich, but the grandson becomes poor.” Today, vegetable growers commonly  use plastic mulch to achieve many of the benefits offered by rock gardening, like retaining soil moisture  and inhibiting weed growth.

But plastic mulch has to be replaced frequently, and the microplastics that end  up in the soil and our food aren’t healthy for us or the planet. So could rock gardening be a low-tech solution, especially in light of our changing climate? After all, it’s not just a historical practice (some Rapa Nui people still  have rock gardens today).

As the planet’s fever keeps getting worse, rock gardening could help protect  crops against extremely hot days. That’s because the turbulent air  flow over the rough surface acts like a soil thermostat, cooling it in  the day and warming it at night. But rock gardening is hard to do at a large scale.

Just imagine the labor involved in  transporting 6,000 softball-sized rocks for a garden the size of a basketball court, let alone the 28 million you’d need  for the average-sized farm in the US. Still, rock gardening could be useful  for small-scale farming in arid regions. It can help farmers be more resilient  to droughts, which are becoming more common and more severe in many parts  of the world due to climate change.

In the U. S. Southwest, for instance, researchers have proposed that  going back to growing agave in rock gardens could be a good way  to adapt to the changing climate.

Rock gardening is just one of many  Indigenous agricultural practices that Western agronomists have long overlooked. And it’s amazing how simple this is, right? Can’t grow stuff?

Try adding rocks! So these tried-and-true practices,  in combination with new technologies, might help us build a more sustainable, more resilient food system  for the centuries to come. [♪ OUTRO]