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The findings of the survey are disconcerting. On a global scale, the meta-collection seems to have reached carrying capacity in both the number of accessions and botanical diversity. While newer collections are being established, especially in the global south, collections in the global north have mostly plateaued or are decreasing in size. Collectively, the overarching trends point towards capacity constraints, underscoring a critical need for strategic prioritisation.

Bucking the global trend

Kirkwood, who co-authored the article, says globally, at least 750 000 threatened plants should be supported by ex-situ conservation. In contrast, South Africa's ex-situ conservation target is equivalent to more than 3 000 plant species: “We suspect South African ex-situ progress across all institutions is fewer than 500 threatened species. The species that require urgent support are even more poorly represented, and institutional capacity is already under pressure."

He says one of this survey's most important take-home messages is that capacity limits are real: “We have to be as strategic as possible in curating collections that meet conservation, research and education goals," he warns.

“Here in the Western Cape, biological diversity is characterised by many species occurring only in very localised areas – many of our plants have global ranges of only tens of kilometres or less. Even a relatively small habitat loss to farming, urban expansion or invasive plants can result in a major reduction or loss of entire species populations. On our doorstep, in the Cape Peninsula, one can find 158 plant species and 3 subspecies only in special habitats between Cape Point and Green Point," he says.

Our huge biodiversity and localised distributions, with modern habitat loss and other major extinction drivers, mean that the Cape is among the world's worst hotspots of plant threat and extinction. Of the 10,744 plants in just the Western Cape Province, for example, nearly 40 per cent are in one of the Red List categories of concern. Red List status is assessed partly by recent reductions in population, and even species listed as Vulnerable or naturally Critically Rare may only have a few hundred plants in total. So, even for less threatened species, any further loss might be catastrophic.

“There is a massive need for capacity to do ex-situ conservation and species recovery. The global targets provide for living collections of 60 per cent of threatened species. Even a far more focused target is challenging. In wild sampling for conservation in extremely threatened species, seeds or cuttings of nearly every remaining plant may need to be sampled and propagated over multiple years in remote or hard-to-access sites. Maintaining viable captive populations for reintroduction to the wild means that source diversity must be maintained, and ideally, each captive population of a species should consist of at least hundreds to thousands of plants," he warns.

Globally, one of the main challenges for botanical gardens is the limitation imposed by the Convention on Global Biodiversity (the CBD), which regulates the acquisition of wild-origin specimens and the international exchange of plant material. The global survey has, for the first time, provided empirical evidence of a drastic decline in both activities after the CBD came into effect in 1993, 44 per cent in the case of wild-origin collections and 38 per cent in international exchanges.

This emphasises the need for increased collaboration and legal material sharing across the network of botanical gardens around the globe that act as custodians of biodiversity. Such an approach will fundamentally reshape the future regional composition of botanical collections and partition diversity across the global network.

This approach makes sense for Kirkwood: “Living collections in the global south are close to biodiversity hot spots, and we can continue strategic collection without contravening the CBD and the Nagoya Protocol."

The SUBG: a regional custodian of biodiversity

Since Kirkwood was appointed curator at SUBG, the garden has contributed significantly to the conservation of multiple critically endangered Cape species by propagating and growing living collections and seedbanking. Some stars of the collection include Haemanthus pumilio, Ixia versicolor, Oxalis fragilis, Pelargonium fergusoniae, Marasmodes undulata, Polhilia groenewaldii, Gibbaeum esterhuyseniae, Gladiolus recurvus, and Ixia leipoldtii.

In the case of Marasmodes undulata, the species was completely extinct in the wild by 2020 and SUBG managed to grow four of the only five living plants from banked seed. Since then, the SUBG has propagated nearly a hundred individuals of this species from seed and cuttings. Working with the national Threatened Species Programme of SANBI, including the Custodians of Rare and Endangered Wildflowers (CREW), the long process of reintroducing plants back into their habitat has started.

SUBG is also trialling strategies to overcome the capacity plateau problem experienced by botanical gardens globally. Kirkwood notes: “While some of our ability to grow our wild and threatened collections recently is a result of starting from a low base, we aim to continue being a positive outlier. One new approach is to hold satellite conservation collections outside formal botanical gardens in non-traditional spaces. One major project was recently started in a corporate head office, providing innovative biophilic plantings and conservation partnership, with all wild material fully owned and managed as part of the permanent SUBG collection and collection database."

Since 2018, Kirkwood has supported other projects to find extra space and capacity to conserve threatened species, including lending institutional and database support to private partners undertaking valuable habitat and species recovery such as the Avondale Open Garden in Durbanville.

SUBG's strategy focuses on building a collaborative approach among botanical gardens, private sector conservation, and the scientific community to innovate, adapt and overcome capacity constraints.

And even though what they can achieve might seem like a drop in the ocean in the context of climate change and the biodiversity crisis, Kirkwood is unequivocal about one thing: the SUBG's “drop" matters a lot.

Caption: The Stellenbosch 中国体育彩票 Botanical Garden (SUBG) is home to the world's largest living collection of Cape Oxalis species, built up by collaborator and taxon expert Prof Leanne Dreyer and representing some threatened species. In the image above, Prof Dreyer inspects the collection with assistant curator Annerie Senekal. 

Photo by Stefan Els

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