Islands are home to one-third of all known plants

Plant life is the fundamental fabric of our planet, and it’s astonishing to realize that about one-third of all known plant species have made islands their home.

Despite representing a little more than 5% of Earth’s land surface, islands are the embodiment of rich biodiversity. How did this happen?

Plant species dwelling on islands

Dr. Julian Schrader from Macquarie University’s School of Natural Sciences, along with an international team of researchers, analyzed data from around 304,103 plants – which essentially sums up all species known to science. The results highlight the incredible biodiversity existing on islands.

Out of 94,052 species that were identified as natives of islands, the team found that a whopping 63,280 are endemic. In layman’s terms, these plant species can only be found on their home islands.

This means that 21% of global plant diversity is tucked away on islands across our planet. The research marks the first-ever comprehensive examination of vascular plants native to marine islands worldwide.

Native and endemic plants

A native plant is one that grows naturally on an island, while an endemic plant species takes it one step further. They’re exclusive to a specific island or a group of islands.

Among these are vascular plants, a diverse group that includes trees, shrubs, herbs, ferns and grasses. They are distinctive from their non-vascular counterparts (like mosses and liverworts), thanks to their circulatory system.

“This is the first time we have had such a complete understanding of which species are where, globally,” noted Dr. Schrader.

“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.”

It also allows researchers to strategize ways of protecting and preserving these unique species. For example, botanical gardens can help by hosting rescue populations.

Island plant paradox

While islands are bursting at the seams with species diversity, it’s alarming to note that only 6% of islands with endemic species are making the cut for a UN goal to protect 30% of land and sea areas by 2030.

The research also shines a spotlight on top centers of plant endemism. These regions are large, tropical islands shaped by a complex terrain and a long history of isolation.

The stars of the show are Madagascar with 9,318 endemic plant species, followed by New Guinea with 8,793 species, Borneo with 5,765, Cuba with 2,679, and New Caledonia with 2,493.

According to Dr Schrader, it’s all about the geography. The physical distance, coupled with unique climates and environments, fuels the evolutionary process, leading to new species creation or “speciation.”

Threats to island biodiversity

However, isolation can be a double-edged sword. Many plant species that have evolved uniquely in such isolated ecosystems may find it hard to compete with non-native species.

Climate change adds another layer of complexity to this situation. The threat is particularly grave for low-lying islands that are susceptible to rising sea levels and extreme weather events.

In this light, the study offers a critical baseline for monitoring changes in islands and plant communities over time. Think of it as a roadmap for prioritizing protection efforts. It’s about the survival of these unique species that dot our planet’s islands, each with their own tale of evolution, adaptation and survival.

“In French Polynesia, I was trying to find one of the rarest plants in the world, the flowering shrub called tiare apetahi (Sclerotheca raiateensis), with only a few individuals left in the wild,” said Dr. Schrader.

This plant holds cultural significance to the local community but is grappling with overharvesting and predation. The solution may lie in botanical gardens, but figuring out how to grow the species outside its natural habitat is the challenge at hand.

The story of island biodiversity is a tale of enchantment, intrigue, and urgent rescue efforts. It’s a narrative that highlights the need for collective action, careful stewardship, and informed conservation strategies.

The study is published in the journal Nature.

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