SYDNEY: Islands have long intrigued explorers and scientists. These isolated environments serve as natural laboratories for understanding how species evolve and adapt. Islands are also centres of species diversity. It has long been speculated that islands support exceptionally high amounts of global biodiversity, but the true extent has not been known until now.
In world-first research published in Nature Today, my colleagues and I counted and mapped the diversity of plant life on Earth’s islands. We found 21 per cent of the world’s total plant species are endemic to islands, meaning they occur nowhere else on the planet.
These findings are important. Island plants are at higher risk of extinction than those on mainland. Detailed knowledge of plants species, and where they grow, is essential for monitoring and conserving them.
Mapping island floras worldwide
The study involved an international team of scientists. We developed an unprecedented database of vegetation information from more than 3,400 geographical regions worldwide, including about 2,000 islands.
The definition of an island is somewhat arbitrary. Conventionally, an island is a landmass entirely surrounded by water and smaller than a continent. This means Tasmania and New Guinea are islands, but mainland Australia, a continent in itself, is not. This is the definition we used.
We found 94,052 plant species, or 31 per cent of the world’s total, are native to islands. Of these, 63,280 plant species, or 21 per cent, only occur on islands.
Endemic species were concentrated on large tropical islands such as Madagascar, New Guinea and Borneo. On Madagascar alone, 9,318 plant species, 83 per cent of its total flora, grow there and nowhere else.
Fewer plant species overall were found in ocean archipelagos such as Hawaii, the Canary Islands and the Mascarenes (east of Madagascar, including La Reunion and Mauritius). However, a large share of their species were still unique to these islands.
Two palms are endemic to Australia’s Lord Howe Island – Howea forsteriana and H belmoreana. They are one of the best-researched examples of “sympatric speciation”, or in other words, species that evolve from a common ancestor at the same location.
This mode of evolution has long been hypothesised to exist. But examples are rare and highly useful for evolutionary research.
The Norfolk Island Pine (Araucaria heterophylla) is, of course, named after the tiny island where it is found. This species, while endangered in the wild, is now widely planted along Australia’s beaches where it is instantly recognisable to us.
Islands are of great conservation concern
Islands cover just 5.3 per cent of the world’s land area but contribute disproportionately to global biodiversity.
Island plants are at much greater risk of extinction than species found in mainland areas, for reasons such as small population sizes, unique evolutionary traits that make them vulnerable to invasive species such as herbivores, specific habitat requirements, habitat degradation, threats from invasive plants and animal species and climate change.
Some 57 per cent of the island-endemic species we assessed are considered critically endangered, endangered, vulnerable, or near-threatened, according to the International Union for Conservation of Nature.
Alarmingly, 176 plant species endemic to islands are already classified as extinct, accounting for 55 per cent of all known extinct plant species globally. Among these is Hawaii’s vulcan palm (Brighamia insignis), which is now considered extinct in the wild. However, the species is popular as an ornamental plant and still survives in gardens.
Other species might be less lucky; extinction in the wild may mean being lost forever.
So, assessing the conservation status of island floras is important. Under a globally agreed United Nations target, 30 per cent of the world’s land and oceans should be protected by 2030. We calculated how much of global islands is conserved today. Disappointingly, only 6 per cent of endemic plant species occur on islands that meet this target.
For instance, New Caledonia, Madagascar and New Guinea, known for their many endemic plant species – contain relatively low levels of protected areas.
Protecting our island plants
Urgent action is needed to protect island biodiversity. This includes expanding protected areas, prioritising regions with high numbers of endemic species, and implementing habitat restoration projects.
Without such measures, the unique floral diversity of islands may continue to decline, with potentially severe consequences for global biodiversity.
Much more research is needed to determine the best conservation strategies for all these plant species. Accurate data is vital to guide future conservation strategies and safeguard against further loss.
Our study also serves as a stark reminder of the urgent need for targeted plant conservation efforts on islands. Many species teeter on the brink of extinction, and time is running out to preserve this irreplaceable natural heritage.

Global warming. Disappearing plant and animal species. Fertile land turning to desert. Plastic in the oceans, on land, and the air we breathe.
These urgent environmental challenges will be in the spotlight over the next few months as the United Nations hosts four major sessions to address key threats to the planet.
– Biodiversity –
First up is a “Conference of the Parties” — a COP — dedicated to biodiversity being held in Cali, Colombia, from October 21 to November 1.
These are called every two years to debate how the world can cooperate to better protect the rich variety of plant and animal life in the natural world.
The COP16 isn’t expected to break new ground but will take stock of progress since the last summit secured historic assurances for biodiversity.
In 2022 in Montreal, nations agreed to place 30 percent of the planet under environmental protection by 2030 in a landmark pact aimed at arresting biodiversity loss and restoring ecosystems to health.
In Cali, countries will put forward national strategies to meet this global objective, and observers hope Colombia as host will provide a model for others to follow.
– Climate –
The world’s most important conference on climate change is this year being hosted by Azerbaijan, a former Soviet republic heavily dependent on oil and gas exports, from November 11 to 22.
While the last summit in Dubai in 2023 delivered a historic commitment to transition the world away from fossil fuels, supporting poorer countries with climate change will top this year’s agenda.
The summit, known as COP29, is expected to land a new agreement on “climate finance“: money from rich nations most responsible for global warming to developing countries vulnerable to climate change.
There isn’t an agreed figure yet, or even consensus on where the money should come from, who should receive it, and what form it could take.
But developing countries are pushing for much more than the $100 billion pledged in 2009. This was only reached for the first time in full in 2022.
The result of the US election, just six days before COP29 begins, could throw a last-minute curveball into the final negotiations, which have proved divisive so far.
It also remains to be seen how many world leaders travel to Baku, the capital on the Caspian Sea, with some expected to focus their energy on COP30 in Brazil next year.
– Desertification –
The least high profile of the three COPs, this session in Saudi Arabia addressing the loss of fertile land to desert is nonetheless critical.
Climate variation like droughts and human activities like overgrazing can result in desertification, a process mainly in dry areas where land degrades and becomes unproductive.
Experts hope the COP16 on desertification, scheduled to take place in Riyadh from December 2 to 13, can act as a turning point in addressing this problem.
“Discussions will focus on ways to restore 1.5 billion hectares of land by 2030, as well as putting in place agreements to manage the droughts that are already affecting many regions of the globe,” said Arona Diedhiou from the French National Research Institute for Sustainable Development.
– Plastic –
In 2022, some 175 nations agreed to fast-track negotiations toward a world-first treaty on plastic pollution, and the final session gets underway on November 25 in South Korea.
The treaty aims to marshal an international response to the plastic trash choking the environment, from oceans and rivers to mountains and sea ice.
Some nations want the treaty to restrict how much plastic can be made while others — particularly oil and gas producing countries that provide the raw materials to make plastic — want a focus on recycling.
Hellen Kahaso Dena, head of Greenpeace’s Pan-African Plastics Project, hopes that countries “will agree on a treaty that prioritises reducing plastic production”.
“There is no time to waste with approaches that will not solve the problem,” the activist told AFP.