Truffula trouble

How New Zealand nearly lost an iconic tree (7 minute read)

It’s almost the end of January, which means I’m coming to the end of my month of making all my articles free. Fridays articles, covering the science behind important issues, will continue to be free for all. Sunday’s articles will focus on nature, in particular the places and plants which are special to me. Mostly, these articles will be for paying subscribers, although I will send the occasional preview and make a few of them free.

I would love for more of you to become paying subscribers, because right now I’m depending on what I earn from my writing. But before I get to today’s article, I wanted to tell you about another way you can have access to paid articles. Through Substack referrals, you can get paid subscriptions – for free – as a reward for sharing The Turnstone with others.

How it works

If you use the refer a friend or the share button on any article, and the person you send it to becomes a subscriber (even a free subscriber), that counts as one referral. If you get two referrals, you earn a free month with full access to The Turnstone. If you get five referrals, you get three months and if you get 15 referrals, you get 6 months. If you are a free subscriber, you will get full access as soon as you’ve got enough referrals, and if you are a paid subscriber, the free months will be counted when you come to renew your subscription.

There’s more information about referrals here. The page gives information for writers first, but if you scroll down there is information for readers.

What are subscriber referrals on Substack? – Substack, Inc

Okay – that’s my marketing pitch over. Now, let’s talk about some amazing trees…

Tī kōuka at Ōtari (image credit: Melanie Newfield)

As a child, I was enraptured by the books of Dr Seuss. The wonderful rhythm of his words, the anarchic nonsense of his plots and his vivid illustrations – all of these had me returning to his books again and again. In my favourite book, the narrator fantasised about turning a vacant patch of land into a fabulous circus, featuring a parade of astonishing animals and dauntless daredevils. There was no particular point to the book – no meaning or message – but I loved it for the sheer extravagance of his imagination.

As an adult, I still think If I Ran the Circus is a brilliant book, but I like The Lorax better. I don’t remember reading it at all as a child, but it’s a book I love to read to children. It has all the absurdity which makes Dr Seuss stories so appealing, but it also has a great plot and message.

In case you aren’t familiar with this masterpiece of children’s literature, The Lorax is an environmental fable about the destruction of truffula trees, as well as the creatures which depend on them. The truffula trees are typically Suessian, a tuft of fluffy foliage atop a skinny trunk. They don’t look as if they are intended to resemble any real plant. But the wonderful thing about nature is that it creates plants and animals as outlandish as any human could imagine, and in New Zealand, we have trees which bear more than a passing resemblance to the truffula.

New Zealand has several types of “truffula trees”. One is familiar to almost all New Zealanders, since it grows from one end of the country to the other – the cabbage tree or tī kōuka. It naturally grows in wet areas such as wetlands and river terraces, but it’s a hardy tree which copes well in cultivation, and that’s where we most often see it. It has a few cousins, one more common in the forest, one at higher altitudes and one from offshore islands. There are also some unrelated trees with a somewhat similar form, and I’ll get to those next week, but none of them are as well-known as tī kōuka.

Tī kōuka, showing leaves and old flower spikes (image credit: Melanie Newfield)

Before the arrival of Europeans, tī kōuka was recognised in whakataukī or Māori proverbs for its ability to come back to life, even after appearing dead. However, since European arrival this resilient tree has been slowly following the path of the truffula tree. Wetlands used to be an important habitat, but more than 90% have now been lost, and losses have continued into the 21^st century. It used to be common to see huge old trees in paddocks – the sole survivors of the original wetlands. But between the draining of the land and the grazing around them, these old trees had no hope of seeding a new generation. By the 1980s, many of these trees were slowly dying from a combination of age and stress caused by their changed environment.

But there was something else, too. In the late 1980s, scientists noticed more frequent deaths among the big, old trees. The leaves of one tuft would turn yellow, then brown, then fall off. Then the other tufts would follow, sometimes wilting before they yellowed. In the space of a few months, every single tuft would be affected, and the tree would be dead – there were no survivors once the symptoms began. Within a few years, the soft, fibrous trunks would have rotted away, and the tree would survive only in memory.

Scientists named the process sudden decline, and soon it was seen throughout the North Island, as well as Nelson and Marlborough. Over 30 years, it killed almost all of the largest trees around most of the North Island, even though younger trees were mostly healthy. South of Levin and in the northern part of the South Island, fewer trees died, but there have still been considerable losses. Only in the areas south of Nelson and Marlborough have the big tī kōuka trees remained largely healthy.

What happened to the trees? The culprit turned out to be an unusual kind of bacteria which is particularly difficult to study because it can’t be grown in artificial conditions. This kind of bacteria is usually spread by sap-sucking bugs¹, and sure enough this one was too. The severity of the disease in different parts of New Zealand seems to relate to the prevalence of one type of bug which feeds on a wide range of species.

But there was something odd – both the bacteria and the bugs were native species. The bug had been described by scientists in the mid-1800s. A disease associated with the bacteria had first been reported by scientists in the early 1900s, although that disease was only known in New Zealand’s native flax, or harakeke. Surely, though, it was known to Māori before that, since harakeke was, and still is, used for many purposes, including weaving clothing and baskets, fibre used in ropes and nets, and as a medicine.

Why did these native bacteria and bugs begin having such a serious impact on tī kōuka in the 1980s, when they had never been reported doing so before?

That’s not yet clear. There are numerous publications about the bacteria, because they are also native to Australia and affect a number of crop species there. However, there are only a handful about the disease in tī kōuka and the New Zealand bugs which spread it. There are a couple of other native plants which are also affected by the disease, including karamū, which is common and hardy, so has been widely planted for forest restoration. One hypothesis is that more frequent planting of karamū resulted in the disease spilling over to tī kōuka. Another suggestion is that without enough native birds to control the bugs, they’ve got out of hand. One source also suggested that there was evidence for previous die-off of tī kōuka. Another suggested that the bug was controlled by fluctuating water levels in wetlands and got out of control when wetlands were drained. In short, we don’t know.

It's also unclear why the big old trees proved particularly susceptible. Perhaps they were under more stress following changes to the environment they had been growing in. At least in the early stages of the outbreak, trees in rural and urban environments were most often affected, rather than those in more natural environments.

In recent years, sudden decline in tī kōuka has been less visible, largely because the large trees are mostly gone in areas where the disease was most severe. However, it hasn’t gone away and reports of dying tī kōuka still crop up. The next few decades will be crucial for tī kōuka if it is to avoid going the way of the truffula tree. The disease has always been worse in warmer areas and in highly modified habitats. The trees will need to contend with a warming climate, which will probably result in more disease in areas which were previously less affected. Unless we can halt the loss of wetlands – something which continues to this day – we are taking away their best chance of survival.

Image credit: Melanie Newfield

1. The word bug can either be a vague term referring to various kinds of creepy-crawlies, mostly but not exclusively insects, or it can be a precise term referring to a group of insects known to scientists as Hemiptera. In this case, I’m using the word bug precisely.