Cambridge University Botanic Garden was the first botanic garden in the UK to grow this endangered tree species. It is distributed in at least 372 botanic gardens globally. Credit: Cambridge University Botanic Garden.

Botanic gardens must team up with others from around the world if they are to play a key role in saving wild plants from extinction.

A major study of botanic gardens around the world has revealed their struggles with one fundamental aim: to safeguard the world’s most threatened plants from extinction.

Researchers analysed a century’s worth of records – from 1921 to 2021 – from fifty botanic gardens and arboreta currently growing half a million plants, to see how the world’s living plant collections have changed over time. 

The results suggest that the world’s living collections have collectively reached peak capacity, and that restrictions on wild plant collecting around the world are hampering efforts to gather plant diversity on the scale needed to study and protect it.

There is little evidence that institutions are managing to conserve threatened plants within collections, on a global scale, despite accelerating rates of elevated extinction risk.

The findings imply that tackling the loss of biodiversity has not been prioritised across the world’s botanic gardens as a collective – a fact the researchers say must be urgently addressed.

Curator of Cambridge University Botanic Garden Professor Samuel Brockington, who led the work, said: “A concerted, collaborative effort across the world’s botanic gardens is now needed to conserve a genetically diverse range of plants, and to make them available for research and future reintroduction into the wild.”

In their report, the researchers say the Convention on Biological Diversity (CBD) has effectively halved the level at which plants are being collected from the wild, and also created obstacles to the international exchange of plants.

Brockington, who is also Professor of Evolution in the University of Cambridge’s Department of Plant Sciences, said: “The impact of the Convention on Biological Diversity is a remarkable demonstration of the power and value of international agreements. But it seems to be preventing individual botanic gardens from working with many globally threatened plant species that we could help save from extinction.”

The study showed that restrictions on wild plant collecting around the world are hampering efforts by botanic garden teams to gather plant diversity on the scale needed to study and protect it. Credit: Brett Wilson/ University of Cambridge.

Collective thinking

As much as 40% of the world’s plant diversity is at elevated risk of extinction.

Acceptance that individual collections have limited capacity to single-handedly prevent species extinction demands a rethink as to how they collaborate to store and safeguard diversity in living collections.

The researchers say it will be vital for the living collections to be considered as a ‘meta-collection’ in future: only by working closely together will the world’s botanic gardens be able to hold the range of plants needed to make a meaningful contribution to conservation efforts.

This will include sharing data and expertise and supporting the development of new collections in the global south, where much of the world’s biodiversity is located. 

The researchers point out that some individual institutions, like the Royal Botanic Gardens Edinburgh, have successfully targeted and measurably conserved threatened conifer species.

Similarly, Botanic Gardens Conservation International (BGCI) has established numerous global conservation consortia. However, these initiatives are the exception.

Wild decline

Plants must be regularly replaced or propagated within living collections: the average lifetime of a specimen is just 15 years. But the team’s analysis found that the number of wild-origin plants – those collected in the wild – in the collections peaked in 1993 and has been in decline ever since. 

Brockington said: “It is certainly not getting any easier to sustain the diversity of our collections.

“This is especially true for wild-collected plants, and they’re the most valuable for us in terms for supporting research, and in finding solutions to the twin challenges of climate change and global biodiversity loss.”

The study indicates that a concerted, collaborative effort across the world’s botanic gardens is now needed to conserve a genetically diverse range of plants, and to make them available for research and future reintroduction into the wild. Credit: Cambridge University Botanic Garden.

Weather worries

As climate change alters growing conditions in different regions of the world, it will become more challenging for individual botanic gardens to continue to grow such a diverse range of species.

Brockington said: “Climate change affects our work directly by altering local weather conditions – we’ve already seen record-breaking temperatures in Cambridge in recent years.

“That’s going to affect how well our plants survive, so we need to think rationally and collectively about the best locations to hold different species across the global network of living collections.” 

Diversity is key

Genetic diversity is important when it comes to protecting plants at risk of extinction, because it allows for breeding populations of species that can adapt to future challenges.

The more individual plants of a particular species in a collection, the greater the genetic diversity is likely to be. 

The team says data from the International Conifer Conservation Programme, run by the Royal Botanic Garden Edinburgh, shows that living collections can make a valuable contribution to conservation efforts – given the right resource and focus.

By distributing threatened species across a network of safe sites, the trees are grown where they grow best, and as a whole they represent a strong sample of the genetic diversity of this important group.

The report is published in the journal Nature Ecology and Evolution.