Remarkable Trees: Biodiversity & Economic Botany

Julia Knights


Following the UN’s International Day of the Forest on the 21st March, Julia Knights spoke to Tony Kirkham, one of the world’s leading experts on trees to learn more about his work, life and book Remarkable Trees co-authored with botanist Christina Harris–which sheds light on 60 of the world’s most extraordinary trees.

Ecology Remarkable Trees 04 cropped cover TK in Russian Far East 1994

Julia Knights: In your bookRemarkable Treesyou share incredible stories of 60 exquisite trees. Tell us about some of your favourites and why? 

Tony Kirkham: So many arboreal friends like the Dawn redwood, but I think one of my favourites is the “Big Lonely Doug”, a Douglas fir, Pseudotsuga menziesii, in the Gordon River Valley, 10km north of Port Renfrew on Vancouver Island, British Columbia, Canada. This is a tree that was left from clearcut in 2011 as it was too impressive to fell. It now stands on its own, the second-largest Douglas fir tree in Canada. I went to see it in 2020 just before lockdown. I was inspired by it.

JK: Which trees support the greatest biodiversity and why?

TK: All trees support biodiversity, particularly in their natural habitat. I must mention the English oak, Quercus robur, and Sessile Oak, Quercus petraea, which supports the greatest amount of biodiversity than any other tree in the UK. A single tree can be host to 2,300 species which include fungi, mosses, ferns, lichens, insects, birds and mammals. And over 300 of these are obligate which means that they can only live on the English oak.

JK:   During your 43 years as Head of the Arboretum at the Royal Botanic Gardens – Kew, you have been on numerous plant collecting expeditions in East Asia, including South Korea, Taiwan, the Russian Far East, Sakhalin Island, China, and Japan to add to Kew’s collection and replace trees lost in the Great Storm of 1987. Any highlights from those expeditions?

TK: Every trip was an adventure, from my first trip to Chile in 1985, driving from Santiago to Puerto Mont in the south seeing Monkey puzzles, Araucaria Araucana, and Alerce trees, Fitztroya cupressoides,  growing in their natural habitat. Visiting the Island of Ulleung Do in the Japanese Sea and collecting seeds of endemic trees such as Ulleung rowan, Sorbus ulleungensis, and a rare maple, Acer okamotoanum,  was amazing, as these are trees that we grow in our gardens but seeing them growing in their natural home was inspiring.

In 1994, I went to the Russian Far East to the Amur Basin and collected seeds of rare trees in cultivation such as the Amur maple, Acer tegmentosum, the Amur maackia, Maackia amurensis, and the Mandchurian walnut, Juglans manchurica. We always work closely with our colleagues in the botanic garden and forestry departments who host our trips. These personnel are imperative at making an expedition go ahead and be successful as they help to obtain the necessary paperwork and international documentation including collecting and export permits. They know their flora and where all the plants can be found in these vast forests, saving time and miles. In Russia we worked very closely with the science team at the Far East Branch of the Russian Academy of Sciences in Vladivostok. All the plant collecting expeditions are focussed on collecting seed (germplasm) for several reasons –to represent the gene pool; to minimise the space and time needed to look after this living material, conservation, biosecurity, and ease of propagation on the return home. It was a difficult trip with the weather. Winter was early in Russia with heavy rain all day and night, raising river levels and restricting access to forests. The nights were cold with brown bears preparing for hibernation. 

I have seen and collected many trees that are very rare both in the wild and in cultivation. In Taiwan we collected a Sapphire Dragon tree, Paulownia kawakamii. There were only 13 trees left in the wild. Today there are more in Kew and other gardens, than in the wild.  In 1996, I was lucky to visit and collect in Sichuan, China. During that trip, I was taken to see a special tree for which we needed permission from the mayor and many others. It was Metasequoia glyptostroboides, the Dawn Redwood. That was special moment. I also trod in the footsteps of one of the most successful plant collectors, Ernest Henry Wilson in China and ended up doing a special project, recounting his steps, and copying his many photographs of trees and the landscape that he took between1908 to 1910 in Sichuan.

JK: The Dragon’s blood tree, Dracaena cinnabari, a stunning slow growing ever green mushroom shaped tree found only on the island of Socotra off the coast of the Horn of Africa, is now at threat and on the International Union for Conservation of Nature (IUCN) Red list of threatened plants due to climate change and grazing. How can trees like this be saved?

TK: We must reduce emissions and slow climate change down to save many of our forests around the world. This will be the first step. We can then look locally at farming techniques and try to change grazing habits etc. Education is one of the greatest controls, but we must provide that in a way that doesn’t come over as being dogmatic and dictatorial. We need to preserve the habitat, not just individual trees to preserve species. So we can fence areas to restrict access to animals and encourage natural regeneration, and plant young trees in these protected areas. We can also collect and store seeds in seed banks such as the Millennium Seed Bank at Wakehurst Place in the UK, where seeds are stored at very low temperatures, preserving the gene pool for the future.

JK: Many trees have multiple uses, such as the Soap bark tree, Quilaja Saponaria, found in the dry forests of Central Chile – used for soap, shampoo, foaming agent in fizzy drinks and in Chile, a traditional medicine for asthma due to the high levels of tannins which help thin mucus and make it easier to cough up. Are there trees for which new uses or active ingredients are still being found?

TK: I suppose a tree like the yew tree, is one that immediately comes to mind. Yews have been such useful trees to humans in the past for making the longbow. But finding Taxol’s in the bark of the Pacific yew, Taxus brevifolia, has been a major advance in the treatment of breast cancer and now the properties of the English yew, Taxus baccata, can be used to have the same effect.   The Maidenhair tree, Ginkgo biloba, is another tree that is rich in antioxidants and continues to be used to treat dementia and Alzheimer’s disease, anxiety, glaucoma, memory and thinking, macular degeneration, premenstrual syndrome and Raynaud’s phenomenon. 

JK: Some scientists believe that trees communicate through an underground network of fungal mycorrhizae. Have you seen evidence of such fungal interactions in your fieldwork? 

One of the most beautiful sights that I witnessed, was in the Californian coast redwood forests. I saw several Albino redwoods, Sequoia sempervirens. They were pure white with no chlorophyl in their leaves at all. Without chlorophyl to photosynthesise, they couldn’t survive on their own – but they were happily growing amongst some of the tallest trees in the world. They must have been networking underground with other trees that were sharing their reserves, food etc. I believe that’s why we need to grow trees in numbers, threes, and fives rather than individual trees that are alone and unable to network. This has inspired me to do more plant health care programmes with trees, mulching around the root plates, to mimic forest floors and provide food for mycorrhizae fungi. We call this biomimicry – copying nature rather than trying to beat her.

JK: With most of the world’s population living in cities, which trees across different climatic zones cope best with high levels of air pollution?

TK: There are many trees that grow well in cities because they are designed to cope with urban air pollution.  The Maidenhair tree, Ginkgo Biloba, is one which loves city life and has been around for millennia, maintaining its ability to cope with high levels of sulphur. So this tree is commonly planted in cities for that reason. The Japanese pagoda tree, Styphnolobium japonicum,tolerates high levels of pollution and is planted like the ginkgo. And of course, the London plane, Platanus hispanica, is one of the most popular city trees because it copes with air pollution. Trees also breathe through their bark, so when the lenticels get clogged and breathing is difficult, they shed plates of bark exposing new clean bark.

JK: With climate change, and the need for us to adapt to a hotter world with more extreme weather such as flooding, drought and more forest fires, how important are our seed banks internationally such as Svalbard Global Seed Vault on the Norwegian Island of Spitsbergen, the National Laboratory for Genetic Resources Preservation in Fort Collins, Colorado and the Millennium Seed Bank at Wakehurst place – Kew in the UK? And what can the public do to support the important work of these seed banks in saving the seed of wild varieties?

TK: Seed banks are the way forward to preserving species –  in a test tube. We are preserving a gene pool that can be used for reforestation at a later date when it’s safe to re-establish these forests. The public can help by becoming a member of Royal Botanic Gardens -Kew as the contributions go towards conservation projects like the seed bank.

JK: Research published in Nature Climate Change in 2022, led by Dr Manuel Esperon from Western Sydney University, estimated that by 2050, about three quarters of tree and shrub species currently growing in urban environments, which help to cool cities, are predicted to be at risk from hotter and drier conditions due to climate change. Given these trees play such a vital role in helping to cool our cities as well as acting as ecosystems for biodiversity, how can we mitigate against this? Should we be growing different tree species in cities?

TK: To mitigate against this, we need diversity in our planting schemes and not to stick with native species but integrate natives with non-natives. Our native trees in the UK number about 35 to 40 and many of these are short lived pioneer species like Birch, Hawthorn, Crab apples and Rowans that will struggle with the changing climate and the introduction of more exotic pests and diseases. We need more shade trees to improve our ecosystem services – the contributions ecosystems bring for human wellbeing and quality of life. Shade trees provide canopy cover to block the ultraviolet rays and lower the temperatures, reduce flooding and soil erosion and a diverse range of tree species will help with this. We need to plant the right tree in the right place for the right reason and keep them stress free and healthy. There is so much literature and help with species selection to help us choose the right tree. We need trees that will match the climate to come in 50 years’ time. We also need to preserve and look after what we have already established.

JK: You led a  “Treeathlon” to support the Trees for Cities campaign for more trees in urban areas in the UK. Tell us more about that?

TK: This was an initiative from the Trees for Cities charity in the UK to raise awareness and funds for urban tree planting. I felt strongly that I needed to support this and be an ambassador, so I trained to run 5K which is exactly the distance around the perimeter of Kew Gardens. After work I was running, training and looking at trees. What more could you want?

JK: The UN COP30 Climate Conference to be held in Belem in Brazil in 2025 should shine a spotlight on the plight of forests such as the Amazon and Atlantic forests and the threat we are seeing of a tipping point in some parts, beyond which the forest ecosystem may turn to savannah. What role do you feel society can play in helping to save trees and forests globally?

TK: We need to support organisations that play a part in protecting the rainforest and education is paramount starting with children to adults explain the importance of these biomes. It should be on the National curriculum in schools as a priority subject.

Ecology Remarkable Trees 00 P1050625 Albino redwood in Federation Grove

Sequoia sempervirens / Albino Redwood © Tony Kirkham

Ecology Remarkable Trees 01 P1070286 Paulownia kawakamii ETOT

Paulownia kawakamii / Sapphire Dragon tree © Tony Kirkham

Ecology Remarkable Trees 02 IMG 4664 Metasequoia glyptostroboides in autumn

Metasequoia glyptostroboides / Dawn redwood © Tony Kirkham

Ecology Remarkable Trees 03 IMG 8561 Quercus petrae Sessile oak Queen Elizabeth I Oak

Quercus petraea / Sessile oak © Tony Kirkham

Ecology Remarkable Trees 04 img948 TK in Russian Far East 1994

Tony Kirkham in the Amur Basin, Russian Federation © Tony Kirkham

Ecology Remarkable Trees 05 DSC 2971 Ginkgo biloba at Zanpukiji Temple

Ginkgo biloba / Maidenhair tree © Tony Kirkham

Ecology Remarkable Trees 06 P1050549 Coastal redwood Sequoia sempervirens in California

Sequoia sempervirens / Coastal redwood © Tony Kirkham

Ecology Remarkable Trees 07 IMG 2304 London Plane Platanus x hispanica Barney at Barn Elms

Platanus x hispanica / London Plane tree © Tony Kirkham

Ecology Remarkable Trees 08 P1060237 Kew Old Lion Ginkgo

Ginkgo biloba / Kew Old Lion Ginkgo © Tony Kirkham

Remarkable Trees by Tony Kirkham, co-authored by Christina Harrison, is published by Thames & Hudson, 2019.

Julia Knights

is the

Ecology & Conservation Editor for Panorama.

A soil and climate scientist, Julia has over 20 years experience in ecology, climate change, sustainable agriculture and conservation as a writer, policy maker, diplomat, and in public engagement. Previously Julia spent 12 years working in China, Russia, and Latin America overseeing major research funding programmes including for UK-Brazil research for new plant species in the Amazon rainforest. Julia is a Fellow of the Royal Society of Biology and a member of the Royal Society’s Committee on Public Engagement.

Tony Kirkham MBE VHM

Tony Kirkham MBE VHM is a world-renowned tree expert and former Head of Arboretum & Horticultural Services at the Royal Botanic Gardens, Kew, for 43 years where he oversaw the management of 14,000 trees, until his retirement in 2021. Kirkham has featured in numerous television programmes about trees and is author or co-author of eight books on plant history and horticulture.


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