Climate Change Alliance of Botanic Gardens: Global Collaboration for Plant Survival in a Warming World

By Tessa Kum, Landscape Succession Officer, Royal Botanic Gardens Victoria

The climate is changing, and botanic gardens are particularly vulnerable. In the coming years, plant species in botanic gardens and urban landscapes will likely confront temperatures they have never experienced before.

Botanic gardens are unique as centres for scientific knowledge and research, playing vital roles in ex situ conservation (away from the plant’s natural habitat), and providing important connection to nature for visitors.

In December 2018, the inaugural botanic gardens Climate Change Summit was held at Royal Botanic Gardens Melbourne. At the summit, 13 international botanic gardens and botanic organisations agreed to form the Climate Change Alliance of Botanic Gardens (CCABG).¹

The CCABG is now a global information-sharing network by which over 500 botanic gardens, arboreta, and similar institutions can share their experiences with managing, mitigating, and planning for climate change. Members may be well-resourced and well-funded, or volunteer-run sites with no budget at all. By facilitating knowledge sharing, the CCABG aids its members to adapt to the challenges associated with climate change.

The issues our world faces are unprecedented and borderless. The lessons learned in the context of a botanic garden are applicable to landscapes beyond their own garden gate. Collaboration between botanic gardens across the globe is essential in understanding how plants will grow and survive in a warming climate.

Why is it so important that botanic gardens around the world adapt to climate change?

In a botanic garden, some aspects of climate can be mitigated. But for the most part, climate cannot be avoided, only endured. Our landscapes are facing climatic conditions not previously experienced, and if we do not plan for these conditions, then these incredibly important landscapes – and the scientific resources they contain – will be severely degraded.

If botanic gardens are to continue their scientific knowledge and research, conservation efforts, and connecting visitors to nature, they must adapt.

What lessons can we apply to the broader landscape?

According to the UN’s IPCC Working Group, under the extreme climate future, where temperatures are forecast to increase by over 3.0 °C by 2070 (assuming worst case emissions),² 20% of tree taxa and 26% of other taxa will be at high risk of extinction.

Botanic gardens need to assess the climate vulnerability risk of their living plant collections so that they can identify priority areas for management intervention. The Climate Assessment Tool (CAT) was therefore commissioned to provide guidance on the likely suitability of plants  for the predicted future climate of a given location.³

The CAT considers current known occurrences of plant species – such as those observed in the wild, in botanic gardens, and in general cultivation – and compares the current climate of these known occurrences to the predicted climate. It uses temperature as a proxy for environmental pressures to consider how a species would be influenced. What previously would have taken hours of research and data compilation, the CAT provides in moments. It gives valuable climate information about a given  site, and an idea of the likely performance of a taxon in a future climate. The CAT removes a lot of the guesswork from species selection, and can inform decision making, while noting that each site is unique, and many other factors will need consideration when undertaking landscape succession.  

The CAT is publicly available online and for free, and has been used by botanic gardens and arboreta, and also city councils and local municipalities, universities and landscape designers.

Similarly, the Landscape Succession Toolkit was published by the CCABG, with thanks to funding from Botanic Gardens Australia and New Zealand.⁴ The Toolkit offers a holistic analysis of the many ways in which climate change may affect a botanic garden, and guidance on how to pre-emptively manage these impacts. Like the CAT it is available online for free and is an excellent starting point for those unsure of where to start with climate adaptation.

Climate change affects everyone, and the CCABG recognises this, and works to strengthen the community by facilitating information sharing, networking and collaboration. The lessons learned by one garden may be exactly the solution another needs, and working together to share this knowledge and develop tools like these benefits everyone.

What decision-making is involved in the protection and management of living plant collections?

A botanic garden is a managed living system. Some plants have the potential to live for centuries, and those are the timeframes which need to be considered when selecting a species to plant. A tree planted now must establish in today’s climate, but also not only survive, but thrive in the climate 30, 50, 100 years from now. There are many factors to consider when selecting a plant to add to the landscape or a collection; future climate suitability needs to be among those factors.

Melbourne’s climate has been warmer and drier in the past 30 years, a trend that is predicted to continue. Redefining our living collections to focus on plants which are suited to this coming climate ensures that we are still able to provide plants for scientific research, maintain ex situ collections for conservation, and provide the public with a world-class landscape.

What research are you currently doing to understand how plants and/or botanic gardens are adapting to climate change?

Research is ongoing and never-ending, and given the pervasive nature of climate change, such learning informs everything we do. One of the most valuable resources any botanic garden has is their horticulturists. The staff who work directly with the plants, and observe them closely from season to season, are a wealth of specialised observational knowledge, and often have an intimate understanding of the nuances of a site.

Our horticulturists trial new plants in the landscape and learn not only what succeeds, but what fails and why. It is the expertise and work undertaken by horticulturists which takes theory and turns it into action in the landscape.

What changes have you noticed in the Royal Botanic Gardens Victoria already at this point (in the last 10-20 years)?

Melbourne’s climate has become drier and warmer in recent decades, and this trend is predicted to continue. An extensive and detailed overhaul of the botanic gardens’ irrigation practices during the Millennium Drought⁵ has safeguarded much of the landscape from this decline in precipitation, but alternative sources of water are still being sought to augment current supplies.

The rise in temperatures makes itself known in myriad ways. As one example, the deciduous oak trees on the Oak Lawn of the Royal Botanic Garden in Melbourne have begun to drop their leaves later and later into the cooler seasons, with some trees never entirely losing their leaves. What effect this will have remains to be seen.

Will we see a shift in the plants that we see in the Royal Botanic Gardens Victoria?

Melbourne Gardens was established in 1846, and the original planting palette – much of which is still present today – reflects taxa from a cooler and wetter temperate climate. As our older trees deteriorate with age, we must consider what species are to replace them. Some species may still be suited to the future, while others are already struggling in our summer heat. The white oak (Quercus aff. alba) that fell in 2019 is an example of this, as it has been replaced with three different oak species that are better suited to the future climate.

Likewise, projects within the landscape are focused on bringing the same resilience to our garden beds. The Australian Drylands Project currently under development will feature native plants that have evolved in drier and hotter climates, and is an excellent opportunity to educate the public and ourselves about plants which are entirely new to Melbourne Gardens.

These changes are important, gradual, and necessary. The purpose of landscape succession or adaptation is to change the Gardens now in order to stay the same for future generations to learn from and simply enjoy.

References:

Climate Change Alliance of Botanic Gardens. Royal Botanic Gardens Victoria. rbg.vic.gov.au/initiatives/climate-change-alliance

IPCC. (2021). Climate Change 2021 Working Group I contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf

Climate Assessment Tool (CAT). cat.bgci.org

Landscape Succession Toolkit. Royal Botanic Gardens Victoria. rbg.vic.gov.au/initiatives/climate-change-alliance/landscape-succession-toolkit

2000s Australian Drought. en.wikipedia.org/wiki/2000s_Australian_drought

‍