Islands are key to protecting plant biodiversity

International research team finds that islands are home to around one in three of world’s plant species

From Tasmania to Madagascar to New Guinea, islands make up just over five per cent of Earth’s land. Yet, a study led by Macquarie University, Australia, and Göttingen University, Germany, reveals that islands are home to over 31 per cent of the world’s plant species. The research shows that of all plants classified as threatened worldwide, more than half are unique to islands. This study provides the first comprehensive assessment of plants - such as trees, shrubs and grasses - which are both native and endemic to marine islands worldwide. Their findings were published in Nature.

The researchers analysed data on more than 300,000 species of vascular plants, meaning those which have a vascular system for water and nutrient transport, unlike plants such as mosses. This group makes up most plant biodiversity on Earth. The researchers analysed all species in this group known to science worldwide, uncovering a treasure trove of island biodiversity. The team found 94,052 species are native to islands, meaning they occur naturally on one or several islands. Of these, 63,280 species are endemic - meaning they are found nowhere else in the world except on a specific island or group of islands - representing 21 per cent of global plant diversity. The team has created a standardised checklist of all known vascular plants occurring on islands, documenting their geographical and phylogenetic distribution and conservation risk. The threats to these plants include habitat loss, climate change and invasive species.

"This is the first time we have had such a complete understanding of which species are where, globally," says Dr Julian Schrader, Macquarie University. "We can now explore the conservation status of some of our rarest plants and come up with distinct strategies to conserve them, such as identifying botanical gardens that could host rescue populations."

This research builds on more than a decade of work around the Global Inventory of Floras and Traits, a dedicated database housed at the University of Göttingen that holds detailed information about where plant species grow, how they are evolutionarily related to each other and which traits they possess. "Our study underpins the surprising importance of islands for global biodiversity conservation", says Holger Kreft, professor at the University of Göttingen and senior author of the study. "Sadly, we find that island ecosystems are currently not adequately protected and that we are losing island species at an alarming rate." The researchers compared the distribution of endemic plant species against the United Nations goal to protect 30 per cent of land and sea areas by 2030 and found that currently 94 per cent of those species occur on islands that are less than 30 per cent protected. Kreft adds, "Beyond the expansion of national parks and other protected areas, the removal of invasive species and the restoration of native habitats is key for effective protection."

Original publication: Julian Schrader et al, "Islands are key to protect the world’s plant endemism", Nature 2024, Doi: 10.1038/s41586’024 -08036-1