According to new research nearly 40 percent of global land plant species can be categorized as very rare, and these species are most at risk of extinction as climate and land use continues to change.

An international team of researchers, including Professor Jon Lovett from the University of Leeds, worked for 10 years to compile 20 million observational records of the worlds land plants. The result is the largest dataset on botanical biodiversity ever created.

They found that there are about 435,000 unique land plant species on Earth. Of these thirty-six and a half percent are exceedingly rare, meaning they have only ever been observed and recorded fewer than five times.

The researchers hope this information can help reduce global biodiversity losses by informing strategic conservation action that includes consideration of the effects of climate change and land use.

In many of these regions agriculture, forestry and urban development is on the rise. Without robust conservation policies there is a real risk to loss of diversity in rare species and because of their low numbers this puts them a greater risk of extinction. Professor Jon Lovett, School of Geography

Their findings are published in a special issue of Science Advances that coincides with the 2019 United Nations Climate Change Conference, also known as COP25, in Madrid. The COP25 is convening nations to act on climate change.

Professor Lovett, from the School of Geography at Leeds, has researched the flora of Africa for 40 years, and is part of the Spatial Planning for Area Conservation in Response to Climate Change (SPARC) research project.

He said: The analysis is the biggest so far for the African continent and really underlines the importance of rarity in the African flora.

It shows how vulnerable many species in Africa are - especially from changes to their habitat. The good news is that many of the rare plants are in places, such as mountains, where they can be resilient to climate change by moving locally. The real danger to them is changes in land use through deforestation, fire and agriculture."

Lead author Brian Enquist, University of Arizona professor of Ecology and Evolutionary biology said: When talking about global biodiversity, we had a good approximation of the total number of land plant species, but we didnt have a real handle on how many there really are.

According to ecological and evolutionary theory, wed expect many species to be rare, but the actual observed number we found was actually pretty startling, he said. There are many more rare species than we expected.

Tundavala Gap in Angola. The western escarpment of Angola is home to many rare plants. Credit: Stephen Eisenhammer, Reuters

The researchers found that rare species tend to cluster in a handful of hotspots, such as the Northern Andes in South America, Costa Rica, South Africa, eastern Africa, Madagascar and Southeast Asia. Many of these regions, they found, have remained climatologically stable over long periods of time, allowing such rare species to persist.

But just because these species enjoyed a relatively stable climate in the past does not mean they will enjoy a stable future. The research also revealed that these very rare species hotspots are projected to experience a disproportionally high rate of future climate change and human disruption.

Professor Lovett said: In many of these regions agriculture, forestry and urban development are on the rise. Without robust conservation policies there is a real risk to loss of diversity in rare species and because of their low numbers this puts them a greater risk of extinction.

Patrick Roehrdanz a co-author on the paper and managing scientist at Conservation International said: This work is better able to highlight the dual threats of climate change and human impact on the regions that harbor much of the worlds rare plant species and emphasizes the need for strategic conservation to protect these cradles of biodiversity.

Further information:

Top image: Jon Lovett with a Welwitschia mirabilis in the Namib Desert of southern Angola. Welwitschia is a living fossil found only in the Namib Desert, and is particularly exposed to the impacts of climate change. Image credit: Stephen Eisenhammer, Reuters.

This work was done in collaboration with the SPARC project (Spatial Planning for Area Conservation in Response to Climate Change), which was funded by the Global Environment Facility and made possible by Conservation International and a National Science Foundation.

The paper The commonness of rarity: Global and future distribution of rarity across land plants is published Science Advances 27 November

For additional information please contact University of Leeds Media Relations and Communications Manager Anna Harrison on a.harrison@leeds.ac.uk or +44 (0)113 34 34196.