Auckland walks: Discovering lichen in Cornwall Park

One of the recent free guided walks around Cornwall Park covered the fascinating topic of lichen, a subject I knew next to nothing about – and still don’t! But I did learn a few interesting snippets from our most knowledgeable guide, Dr Dan Blanchon, a lecturer at Unitec and New Zealand’s only lichenologist.  

The basalt rock of Cornwall Park’s ancient lava flows provides a good environment for lichen so the park is rich in species and plentiful in examples. Lichens actually help to erode the rock they live on but this happens so very slowly that any change to the rock would only be noticeable over hundreds, if not thousands of years. Also, for those of you who have lichen living on their garden trees, the lichen won’t kill the trees – they are, apparently, a sign of the tree’s decline.

Some lichens also live on metal, as you can see on this drainage grate. I thought Dan said this was called the ‘sexy path’ lichen, but perhaps I mis-heard (imagined?) that as I can’t find that name anywhere. I do recall though that he said this particular lichen has a chemical in it that has Viagra-like properties.

Lichens seem to contain quite a diverse range of chemicals, which is one excellent reason for studying them. The lichens themselves use chemicals (and smothering) to try to kill each other – lichen warfare, who knew? Many lichens contains chemicals that are used in dyes – there is, for example, one particular lichen in Thailand that is cultivated specifically for the pretty pinkish purple dye it produces. Some lichens are used in the manufacture of sunscreens as they contain chemicals that protect against UV-B irradiation, and others have anti-fungal and anti-biotic properties. One example of this was the Old Man’s Beard we saw growing on a kauri tree. Several of the different varieties of Old Man’s Beard (Usnea) contain antibiotics, something recognised by indigenous cultures around the world – American Indians used a local variety to bind wounds and, here in New Zealand, Maori also realised the lichen’s special properties, naming it angiangi. (It is still used in a herbal dietary supplement, according to the Kiwi Herbs website.)

Don’t go nibbling on the next lichen you see though. Lichens are mostly indigestible, though reindeer and caribou are known to eat some lichens in the harsh conditions of a northern winter when there is little other food available.

A lichen is a complicated beastie – it is not actually one single organism but rather a fungus living in a symbiotic relationship with a photosynthetic partner, which might be a green alga or a cyanobacterium or both. The fungus is the farmer and the alga and/or bacterium produce/s the food it survives on.

Lichens don’t grow near soil – the nutrients in the soil are too rich and kill the lichen, which is why you don’t usually see lichens growing on the lower parts of walls, as soil nutrients get splashed up on to the wall surface during rainfall. Some lichens are sensitive to the nutrients in urine, so are killed by dogs peeing on walls and the bases of trees. Lichens are also highly sensitive to air pollution so will not grow in polluted places. If you see lots of lichens growing on the trees, rocks, etc., in your area, take it as a sign of clean air.

As you see, no lichens are growing on the lower portion of this wall

If you get the opportunity to look at lichens under a microscope, you’ll be amazed to find they are teeming with life: tiny mites, snails, and weevils are just some of the little creatures you’ll see. And, because of these micro-organisms, lichens are also beneficial to other creatures, like the birds that eat all those little bugs, so try to resist the temptation to kill the lichen you find growing on the rocks and trees around your home and garden.

Although we were told the names of many of the lichens we discovered during our two-hour wander around Cornwall Park, I’m not going to include the names here for fear of wrongly identifying the lichens in my photos. Suffice to say, New Zealand has an exceptionally rich lichen flora, with over 2000 species already named and probably twice that number still to be discovered, categorised and named. Considering the potential benefits to humankind of the chemicals in lichens, I think this country needs more than one lichenologist!

If you want to discover more about these incredible organisms, our guide recommended Allison Knight’s Lichens of New Zealand: An Introductory Illustrated Guide, published by the Botanical Society of Otago and available as a pdf download.  

Auckland trees: The Chinese trees of Cornwall Park

Earlier this week I enjoyed a most enlightening guided walk in Auckland’s Cornwall Park, exploring the Chinese trees with specialist tree guide and eminent botanist Dr Mike Wilcox. Mike was assisted this day by Estella Hin Ling of the Auckland Botanical Society, whose job it was to translate Mike’s words into Cantonese as, not surprisingly given the subject and Auckland’s large Asian population, our party included a large number of local Chinese.

The walk was just one of a series of free events run by the folks at Cornwall Park to help Aucklanders appreciate even more this glorious green haven – though, judging by the numbers of people walking, jogging, strolling and picnicking, the locals are already keen users of the 172 hectares gifted to the people of Auckland by John Logan Campbell in 1901. The events are many and varied, and I recommend you keep an eye on their website for something that might interest you.  

Here, then, are some of the beautiful Chinese trees we discovered during our two-hour walk, along with just a few of the facts Mike shared with us. Take the walk yourself to find out more.

Ginkgo tree (Ginkgo biloba)

Having been on this earth for around 200 million years, the gorgeous ginkgo, possibly my favourite tree, is a living fossil. It has probably survived so long because it was considered sacred by Buddhist monks, who cultivated the tree near their temples. It also has no pests or diseases, and individual trees can live for as long as 1000 years. The ginkgo has a fan-shaped leaf like no other tree, and the fruit of the female tree smells like human vomit. Despite this revolting fact, the Chinese cook and eat it, and they use the leaves to make medicine which is supposedly good for the brain.

The grove of ginkgoes in Cornwall Park was planted in the mid 1960s on the former site of Cornwall Hospital, following the removal of the hospital buildings.

Dawn redwood (Metasequoia glyptostroboides)

In Cornwall Park, the small group of Dawn redwoods – one tall specimen and several less mature trees – are towered over by a stand of Californian redwoods, though both are tall and majestic trees. During the last ice age, the Dawn redwood was almost wiped out, surviving only in isolated valleys in remote parts of China. It is still rare in the wild, and is now state protected in China. In autumn, its leaves turn a subtle shade of apricot, as you can see in my photos.

Tree of heaven (Ailanthus altissima)

Although often seen in street plantings around Auckland, the Tree of heaven is not popular with the city council staff who maintain the streets, partly due to its habit of persistently sending up suckers and partly due to its foul-smelling leaves. The tree has white flowers and orange fruit and can be identified during the winter months, when its branches are bare, by the snake-like marks on its bark.

Mike Wilcox (holding a Plane tree leaf) and Estella Hin Ling, with the distinctive bark of  a Plane tree in the background

Plane tree (Platanus acerifolia)

I’ve always thought of the Plane as an English tree but it is just as familiar to the Chinese, though it only flourishes in some parts of that huge country. In Auckland this was a hugely popular tree for street plantings in the early 20th century, as witnessed by some of the magnificent Plane-lined streets in Ponsonby and other inner-city Auckland suburbs.

China berry (Melia azedarach)

This is another popular street and home-garden tree, with pretty autumn foliage and little yellow berries that remain on the tree through much of the winter. The berries are toxic to humans but many birds love them. Though underutilised for its timber, the China berry produces medium-density straight wood of a brownish-red colour that is resistant to most wood-eating insects.

Wonder tree (Idesia polycarpa)

This is such a graceful tree and, with its hanging bunches of bright red berries, it not only looks attractive but birds love it. The berries can, apparently, also be eaten by humans, either raw or cooked. The leaves when they fall in the autumn are particularly crunchy underfoot, perfect for walking through, kicking up and playing amongst – yes, I am just an old kid at heart!

Chinese sweet gum (Liquidambar formosana)

The gum of this Liquidambar can be burned for incense, hence its common Chinese name. In Auckland the American Liquidambar is a very popular tree and can be seen in street, park and garden plantings throughout the city, providing spectacular autumn colour. I learnt the difference between the two varieties during my walk – the Chinese variety has a three-pointed leaf shape, whereas the American type has five points (see photo above). Mike Wilcox told us the tree in Cornwall Park is the only Chinese variety he has seen in Auckland so if you spot another, make sure to let the park authorities know.

Mike Wilcox is the author of Auckland’s Remarkable Urban Forest (Auckland Botanical Society, Auckland, 2012), which describes the trees and forests of Auckland and includes those in parks and reserves, on campuses, school grounds, cemeteries, and at historic homesteads – it’s a great book and highly recommended reading.