A new study from the University of Southampton has found that human settlement in South Pacific islands is reducing the variety of plants.

Researchers have found that during approximately the last 3,000 years the range of plant species has reduced – a process which scientists call ‘homogenisation’ - which correlates with human migration to the area.

Professor David Sear of the University of Southampton, who was one of the supervisors, said: “The implications of this research are that human arrival rapidly impacted the floral communities on tropical islands that previously showed great variety in their native flora, owing to their dispersed and isolated locations.

"The Polynesian and Lapita peoples in effect manipulated their islands to support their populations – in so doing they homogenised a previously biodiverse archipelago of tropical islands.

“Our findings will help Pacific islanders better understand how their ancestors adapted to climate and natural hazards, but also gain a richer knowledge of the ways in which they altered the islands they inhabit.”

The research was carried out by a team from across Europe, Australia, New Zealand and the USA – led by the University of Southampton with the Universitat Autònoma de Barcelona and University of Bayreuth.

They examined fossil pollen records from 15 swamp and lake sites on 13 islands in the South Pacific before and after humans moved there.

People moved to the South Pacific in two stages.

The main migration event was to western Polynesia, Melanesia and Samoa around 3,500 to 2,800 years ago.

Later, around 1,000 to 700 years ago, people spread further east to the remaining islands, such as French Polynesia and Rapa Nui (Easter Island), north to Hawaii and south to Aotearoa (New Zealand).

None of the islands had previously been inhabited.

The researchers conclude that humans modify flora soon after they settle within an area. They introduce new, non-native plants and animals which they have brought with them and undertake activities to help them survive, such as agriculture, the building of settlements and the use of fire to clear land.

Interestingly, the study also showed that areas of land at a higher elevation retained more distinctive flora, probably because they were less likely to have been inhabited and impacted by humans.

Findings from the study are published in the journal Nature Ecology and Evolution.

The research was supported by UKRI grants and a SPITFIRE Doctoral Training Centre Studentship fund.