Scientists Found an Unlikely Culprit Driving Catastrophic Deforestation in Chile's Easter Islands

The deforestation of Rapa Nui, also known as Easter Island, has been a subject of intrigue and mystery among scientists. Humans were held accountable, but a recent study proves another tiny culprit behind the destruction. Dr. Terry Hunt from the University of Arizona and Dr. Carl Lipo from the University of Birmingham analyzed the contribution of Polynesian rats (Rattus exulans) to the massive deforestation and found shocking results. The study published in the Journal of Archaeological Sciences showed that the rat species massively populated Easter Island. A single pair of rats' infiltration may have resulted in a whopping 11.2 million population in 47 years. In that duration, the tiny creatures devoured almost 95% of the palm trees.

Rapa Nui deforestation has been a debatable topic among environmental archaeologists, as is the role that the Polynesian rat might have played. The area was once a heavily forested region with about 15 to 19.7 million Rapa Nui palm trees. Greenery remained until human-led deforestation almost destroyed it between 1200 and 1650 CE. When Europeans arrived in 1722, only scattered palm trees and shrubs were left in the area. "Review of historical observations indicates that grasses and small shrubs dominated the vegetation Europeans encountered in the 18th century," said Dr. Lipo. "A stark contrast to the palm-dominated landscape that existed at the time of colonization," he added, as per Phys.org.

For the longest time, humans were solely blamed for the crisis that hit the Pacific island decades ago. Although the involvement of rats was acknowledged, it was never deeply explored. Many researchers have argued that the destruction caused by rats was fairly insignificant. Andreas Mieth and Hans-Rudolf Bork conducted a study on R. exulans, a Pacific rat species, to analyze its contribution to the Rapa Nui destruction. Criticising previous findings, the researchers claimed that the rats had a negligible role in the deforestation. "Our investigations arrive at the definite conclusion that humans, and not rats or climate variations, destroyed Rapa Nui’s palm woodland," they added.

However, Dr. Lipo believes that the Rapa Nui palm trees were especially susceptible to rat predation. "Jubaea chilensis, the palm species on Rapa Nui, produces large seeds (similar to small coconuts) with thick shells but extremely high nutritional content. These seeds are rich in oils and carbohydrates," the doctor explained. "For rats, each palm nut represents a substantial energy reward worth the effort to gnaw through the shell," he added. He claimed that palms produce fewer seeds per tree, and with rats eating most of them, the regeneration of the trees is stunted. "The reproductive strategy of producing few, large, energy-rich seeds made palms particularly vulnerable to a seed predator achieving high population densities," Dr. Lipo said.

The predation issue was exacerbated by the increasing population of rats. While humans were uprooting the palm trees, rats were nibbling on the seeds, removing any chances of regeneration. This combined exploitation has led to the complete deforestation of the island by 1600 CE. "People cleared land for gardens near the coast, but the rats preceded them in number and spread over the island," said Dr. Hunt. "Our study dramatically revises 'ecocide' into a story of an invasive species on an isolated island," he added. However, the researchers acknowledged that the Rapa Nui destruction was accelerated by the actions of the people, who transformed a natural land to satiate their agricultural requirements.