The ecological shifts experienced on Easter Island (Rapanui) represent one of the most illustrative yet contentious examples in environmental archaeology. This discussion centers around the Polynesian rat (brown rat) amid the island’s deforestation, an event that wiped out an estimated 15 million to 19.7 million palm trees, specifically the palm tree (pashalococcos disperta) between approximately 1200 and 1650 AD.

Prior to human settlement, Rapa Nui was dominated by large palm trees of now-extinct varieties, including the Chilean wine palm (Jubaea chillensis).

These majestic trees can survive for up to 500 years, but are slow-growing, taking around 70 years to mature and bear fruit.

By the time Europeans arrived in 1722, very few palm trees remained. When European interest in the island’s ecosystem peaked, these trees had largely disappeared.

“European accounts often describe islands devoid of trees, yet they also mention palm trees and their fronds,” notes Carl Lipo, a professor at Binghamton University.

“It’s uncertain whether they used this term to denote other types of trees.”

When exploring new islands, Polynesians transported various subsistence items such as taro, sweet potatoes, bananas, yams, dogs, chickens, and pigs, along with the omnipresent Polynesian rat.

In contrast to the Norway rat (brown rat), which was introduced post-European contact and favors the tree canopy, this smaller arboreal species provides a wealth of information for researchers.

“Their genetics showcase unique haplotypes due to the ‘founder effect’,” explains Professor Lipo.

“The genetic diversity of rats as they traverse the Pacific allows us to trace human migrations and the frequency of these settlements.”

The methods by which these rats entered Polynesian outrigger canoes is debated. Were they stowaways or intentionally included as a backup food source? Ethnographic evidence leans toward the latter.

“After European arrival, a naturalist collecting specimens for the British Museum witnessed a man walking with a mouse, who informed him it was for lunch.”

Additionally, rat bones have been uncovered in midden deposits, or ancient refuse piles, on various Pacific islands.

Upon their arrival at Rapa Nui around 1200 AD, the rats discovered a predator-free paradise filled with their preferred foods.

Their population surged into the millions within a few years, as they can breed multiple times annually.

“The palm fruit was like candy to the rats. They turned into a significant food source,” Professor Lipo commented.

Rapa Nui’s palm trees had coevolved with birds and did not develop the boom-and-bust production cycle that would have enabled some nuts to withstand rodent exploitation.

As a result, rats consumed the palm fruit, preventing the next generation of trees from establishing.

Simultaneously, humans cleared land for sweet potato fields. This dual pressure led to the deforestation now characteristic of the island.

Alongside plants and animals, Polynesians also incorporated practices such as slash-and-burn agriculture to enhance soil fertility.

Old volcanic islands like Rapa Nui possess poor soil, and rainfall depletes nutrients.

Clearing or burning parts of the forest temporarily rejuvenates soil quality.

Once nutrients are exhausted, farmers relocate, the land recuperates, and trees regrow.

“This pattern is also observable in New Guinea and other regions across the Pacific,” Professor Lipo mentions.

“However, in Rapa Nui, the slow growth of trees and the rats consuming coconuts inhibited regrowth.”

Eventually, the islanders shifted to a farming technique that utilized stone mulch to enrich their crops.

While the reduction of palm forests marked a significant ecological transformation, it was not a disaster solely orchestrated by humans.

The islanders’ survival did not hinge on the palm trees; rather, it depended on the availability of cleared land for agriculture.

Moreover, palms are not hardwoods; they belong to the grass family and do not provide material for canoes, homes, or fuel.

“The loss of palm forests is unfortunate, yet it wasn’t catastrophic for the people,” states Professor Lipo.

“They didn’t rely on them for survival.”

Though some palms may have persisted into European colonization, the introduction of sheep farming in the 19th century likely sealed their extinction, as any remaining seedlings would be consumed by sheep.

Ironically, the Polynesian mouse suffered a similar fate to the palm trees, being outcompeted by Norway rats or predated by non-native species like hawks on most islands.

Despite changes in species, islanders still discuss the rodents’ cyclical population booms and severe declines.

The narrative of Rapa Nui exemplifies unintended consequences as well as resilience and adaptability in one of the most remote inhabited islands, with its closest neighbor situated 1,931 km (1,200 miles) away.

“A more nuanced perspective on environmental change is essential,” says Professor Lipo.

“We are integral to the natural world and often modify it for our benefit; however, this does not necessarily imply we are creating an unsustainable environment.”

Findings from this study will be published in the archeology journal.

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Terry L. Hunt and Carl P. Lipo. 2025. Re-evaluating the role of Polynesian rats (brown rat) in the deforestation of Rapa Nui (Easter Island): Faunal evidence and ecological modeling. archeology journal 184: 106388; doi: 10.1016/j.jas.2025.106388