News published: 21 November 2022

New report shows importance of tree diversity for ecosystems + people in a changing climate

In the Curepipe Botanic Gardens on the Indian Ocean island of Mauritius lives the loneliest tree in the world. Propped up by scaffolding, with drooping leaves and a scarred trunk, the ailing 150-year-old palm is the world’s last known specimen of Hyophorbe amaricaulis. To date, no one’s been able to propagate it, so when it dies, that’s the end of the species.

While it might well be lonely, the tree is by no means alone in its predicament. Last year’s State of the World’s Trees report found that of the more than 60,000 known tree species, at least 17,500 are threatened with extinction, with 440 species down to fewer than 50 individuals left in the wild.

According to a new report, ‘Conserving and using tree diversity for global climate change adaptation and food system resilience’, this dwindling of tree diversity is damaging to our planet’s ecosystems – and ourselves – and constrains options for successful adaptation to the changing climate. We can prepare ourselves far more effectively for today’s challenges and those to come — but we’ll need trees to do it.

The report was launched by the Crop Trust at the Global Landscapes Forum (GLF)’s annual Climate event, held alongside the United Nations Climate Change Conference (COP27) in Sharm El-Sheikh, Egypt. It was written by Lex A. J. Thomson, an agroforestry and forestry scientist, botanist, and rural development advisor and associate with the Australian Centre for Pacific Islands Research, who spoke during the launch.

“We’ve been gifted with this remarkable tree diversity, which can be used for so many different purposes. As well as diversity at the species level, there’s also the intraspecific, or ‘within species’, diversity, which is just so important for the conservation and use of these trees. There’s so much we still have to learn about arboreal biodiversity.”

As a case in point, Thomson explained how in Micronesia, in the Pacific Ocean, communities have selected and cultivated edible varieties of the pandanus tree, which offers a food supply that’s high in Vitamin A and resilient to climatic shocks. “We’ve found that when there’s a drought in these coral atoll areas, coconuts and other trees will stop producing fruit, but the pandanus can keep producing during those difficult periods.”

Yet the majority of current tree-planting commitments toward reforestation and climate mitigation agreements (like the Bonn Challenge and the Paris Agreement) fail to take the importance of tree diversity into account, said Paul Smith, Secretary General of BGCI, which co-sponsored the report.

Instead, commercial plantations – usually of exotic species – dominate the plans. “We know how to grow around 18,000 different tree species,” he said. “But in mainstream forestry, we use a tiny fraction of that.” Monoculture plantations of fast-growing exotic species like eucalyptus and pine are favoured – and these can have damaging impacts on local ecosystems, such as soil degradation, erosion and groundwater decline.

“Native tree species can deliver much better ecosystem functioning, biodiversity and resilience effects.” Paul Smith, Secretary General of BGCI,

Tree diversity in agriculture can also lead to improved crop yield and fewer issues with pests and diseases – essential services as climate change brings new hazards and constraints.

“We need to look at species-rich, multistrata approaches to agroforestry systems, and ensure that we’re using local indigenous trees,” said Sarada Krishnan, a coffee scientist and director of programs at the Crop Trust. “We can also use some of the more desirable exotic species, as long as they are not invasive and are combined with indigenous trees in the right way.”

To scale out the implementation of such systems, she said, it will be critical to build seed sources and private nurseries that meet farmers’ and foresters’ demands for high-quality tree germplasm.

Ramni Jamnadass, a tree resources scientist based at the Center for International Forestry Research – World Agroforestry (CIFOR-ICRAF), also involved in preparing the report, made an impassioned call for more finance for this critical sector.

“Tree diversity is a key contribution to solving some of our global problems; however, the resource is under severe threat,” she said. “Investing in tree-planting material is an obvious starting point to boost diversity, and should be a no-brainer for governments and funders”, she said, adding, “the investment will pay itself back many times, for the betterment of the climate, biodiversity, and food and nutritional security.”