More than a fifth of the Earth’s plant species are found only on islands, making them one of the largest biodiversity hotspots, a breakthrough global study has found. This conclusion has pushed the scientists behind the study to advocate for added protections of these unique ecosystems.
For the first time, researchers mapped more than 300,000 plant species known to science and found that 21%, or 63,280 species, were endemic to islands, meaning they have not been found in the wild anywhere else.
For years, scientists relied on rough guesses about the number of plant species native to islands. Now, with a comprehensive database, researchers can pinpoint exactly which species call these islands home, assess their conservation status and calculate precise figures for large-scale analyses.
“This information is extremely valuable for both research — enhancing our understanding of the drivers of endemism and island biodiversity — and for conservation,” lead author Julian Schrader, an ecologist at Macquarie University, told Mongabay in an email.
The study also found that 55% of all plants that have already gone extinct were on islands, even though they constitute just 5% of the Earth’s land surface. Of the endemic species remaining on islands, 51% are now threatened and 70% are found only on a single island.
“Very worryingly, of all single-island endemic species, only 6% occur on islands currently meeting the United Nations 30×30 conservation target,” wrote Holger Kreft, one of the study’s authors, meaning that most are in unprotected areas with a higher risk of being impacted by human activities.
Urban development and agriculture driving land use change have largely driven the decline of tree species on islands, according to a recent assessment by the International Union for Conservation of Nature. Invasive species, disease and climate change have also contributed.
Island species have flourished for millennia with little competition, but when invasive species and pests are introduced, often by humans, they often struggle to survive.
“Island plants are disproportionately threatened by extinction,” Schrader said. “When exposed to non-native herbivores or plants, native island species often lose out and, in extreme cases, become threatened or even extinct.”
The authors stressed that more effort needs to be made to protect wild plant life on islands.
Plants on islands like Madagascar, once connected to the African continent, include ancient lineages that have long gone extinct elsewhere. Other islands, such as the Galápagos, which erupted into existence from below sea level, host rare plants that managed to reach their distant shores and then evolved under extreme isolation, often breaking off into several subspecies.
“The nations to which these islands belong may not have the financial resources to conserve biodiversity,” Schrader said. “I believe that wealthier, more developed nations especially need to support those island nations that have many endemic plant species.”
Banner image: The dragon’s blood tree (Dracaena cinnabari) on Yemen’s Socotra Island is an endemic tree listed as vulnerable by the IUCN. Image by Rod Waddington via Flickr (CC BY-SA 2.0).
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