Trees and Fire - a forester's perspective

A firefighter retreats from the intense heat of exploding eucalyptus trees in an Australian bushfire

In a letter to the editor of The West Australian newspaper not long ago, I suggested that people building new homes in bushfire-prone areas in south-western Western Australia should consider planting northern hemisphere deciduous hardwood trees rather than native eucalypts like jarrah (Eucalyptus marginata) and marri (E. calophylla), or that perennial Australian favourite, the lemon-scented gum (E. citriodora).

I have also opposed the planting of eucalyptus trees (especially the tall forest trees) as street verge trees in suburbs close to bushland.

The eucalypts not only drop their leaves and shed bark in the height of summer, filling gardens and gutters with dry leaves, bark and twigs, but contain volatile and flammable oils in their foliage which explode when ignited. For anyone who doubts this, it is a very instructive experience to place a leafy branch, freshly fallen from a eucalyptus tree onto a bonfire. It smokes momentarily, and then suddenly bursts into intense flame. This explains the phenomenon of the “fire ball” observed by many firefighters – the entire crown of a tree, bombartded with embers from an approaching bushfire, suddenly explodes en masse, and a ball of fire rolls through the air into the next tree, setting it alight, and so on.

A live eucalyptus tree instantly transformed into a fireball by an intense bushfire

Most non-eucalyptus hardwood trees (usually referred to in the Northern Hemishphere as “broadleaf” trees), on the contrary, are relatively non-flammable. The green foliage is very hard to ignite and smoulders rather than bursts into flame. These trees have the additional advantages of the lovely colours of the foliage in autumn, and (being deciduous), allowing access to winter sunshine.

Deciduous hardwood trees (sweetgum and flowering plum) on Jack and Sue Bradsaw’s semi-rural block in the south-west of WA: providing summer shade, winter sun and non-flammable leaves

Based on the responses to my newspaper article, my promotion of deciduous trees seemed to go down like the proverbial. Environmentalists and devotees of native gardens disagreed, often with passion. To these people exotic (or "non-Australian") trees are an anathema. On the other hand, few supporters of native gardens and eucalyptus street trees ever seem to give much attention to the bushfire consequences of their landscaping.

There is nothing new about my suggestion. Nor do we lack for confirmation of the principle. There are many examples of stands or plantations of broadleaved trees such as the cork oak (Quercus suber) not only surviving an intense bushfire but helping to dampen its intensity. There were numerous examples in the Black Saturday bushfies in Victoria where a single English oak (Quercus robur) sheltered and saved a house from destruction.

Some Australian trees have the same characteristic, for example the Illawarra Flame tree (Brachychiton acerifolius) from the rainforests of Queensland, and several of the kurrajongs (also Brachychiton species). In my book on the 1961 bushfires (Tempered by Fire) there is a graphic story of a group of firefighters sheltering from the infamous Dwellingup bushfire in a citrus orchard, and surviving unscathed.

Recent bushfires in the outer suburbs and the semi-bushland surrounding Perth have brought all this to mind. Most of the houses lost in the fires were surrounded, or overtopped by eucalyptus trees which burned so fiercely that firefighting was rendered futile. In the 2021 Wooroloo Fire, one of the residential areas that was almost completely obliterated by the fire had karri (E.diversicolor) trees planted as street trees, perhaps the most inappropriate urban tree planting I have ever heard of (karri trees grow to 80 metres in height). They burned so intensely all attempts at firefighting were impossible.

My newspaper article was written in response to being contacted by people who understood this: they wanted to plant trees on their property, and they wanted the pleasure of avenues of street trees, but they did not want a bushfire hazard. Moreover, they were confused by the conflict between people promoting native trees and those promoting bushfire safety.

By coincidence, just at this time I was happily reading H.L Edlin’s wonderful book Trees, Woods and Man, a 1956 edition of which I picked up for a few dollars in a second-hand book shop in Fremantle. Edlin was an English forester in the 1930s and 40s, and his book, although rather old-fashioned, is still a delightful account of forestry and forest history in Great Britain. I have found it full of fascinating personal observations and interesting illustrations.

English forester H.L Edlin inspects a stand of young ash trees, leafless during the winter months and almost unburnable in summer

There is almost nothing about bushfire management in Edlin’s book, as you would expect for a treatise on forestry in Britain, where forest fires rarely, if ever occur. When they do (unless they occur in plantations of introduced and flammable conifers like Scots pine or Norway spruce), they are usually controlled without difficulty.

However, one brief section of Edlin’s book caught my attention. This is where he recalls his work as a forester in southern England during the Second World War:

I write with exceptional experience of the risks of fire to wood­lands of different kinds, as from 1940 to 1945 I was concerned with fire-fighting arrangements over many thousands of acres of forest in the South of England. Besides the usual hazards, these [forests] were subject to unusual risks [during the War] from large-scale military training and aircraft, and in particular to occasional showers of German incendiary bombs; so, over this long period of varying weather conditions, it is safe to say that any kind of vegetation that could be set alight, was set alight, and had of course to be tackled by fire-fighters. Broadleaved woodland of any kind simply refused to burn at any time, although fires in coniferous plantations, and among heather or gorse, were serious and frequent …

I have always regarded the work of the urban fire and rescue brigades at the time of the Blitz with the greatest admiration. But now it seems I should also admire the unsung work of British foresters who “did their bit” in the control of forest fires during the war years. It is a story yet to be told, or at least it is one of which I had not previously heard. I was also pleased to read that Edlin confirms that the “broadleaved woodland” (which comprises deciduous trees such as oak, ash, elm and beech) would not burn, even when showered with incendiaries.

Reading about all this, I wondered whether the Army’s forestry companies raised in Australia and sent to the UK during World War II (of which my uncle Geoff Chandler was an officer) became involved in forest fire-fighting. Many of the Australian foresters and timber workers who joined the Army’s forestry companies to harvest and process timber in England and Scotland in the early 1940s would have brought first-hand bushfire experience with them, and would have been a very handy addition to Forester Edlin's fire crews.

Members of the Australian forestry company in Scotland during the War (Painting by Colin Colahan in the Australian War Memorial

I am also reminded of a proposal put to me in the wake of the 2009 Black Saturday bushfires. To minimise the bushfire problem in Victoria, it was suggested, the native eucalypt forests on national parks and State forests in and around Melbourne should be cleared and replanted with English oak This would neutralize their bushfire hazard.

When hearing this I first smiled quietly, imagining the apoplexy of certain botanical academics when confronted with this proposal. But then the forester in me kicked in. I had to tell the proponent that I could not agree with her. I love our native eucalypt forests and their role in Australian society, culture and industry, and I have spent the best part of my life trying to conserve and protect them. The bushfire threat that native forests present to humans living within, or up against them is not the fault of the forests – it is an artifact of post-European settlement and of contemporary forest mismanagement.

Moreover, it is a problem that could be easily minimised if forest managers were prepared (or were allowed) to reduce bushfire fuels in Victorian eucalypt forests with mild-intensity prescribed burns. This was the approach the pre-1788 Aboriginal forest managers understood to perfection, and is still understood and practiced in Western Australia, but which became politically-incorrect in Victoria and NSW when the wrong people gained control of the forests.

In short, my view is that the best place for our native bushland trees is in the bush, not in the backyard. And in the bush, bushfires should be managed by the methods employed with success over many thousands of years by Aboriginal people, and by enlightened Western Australian foresters.

Unfortunately, backyard forests have sprung up throughout bushfire-threatened suburbs all over southern Australia, especially in those greenfields residential areas appearing almost overnight on former farmland and where property owners have been encouraged to establish native gardens and plant eucalyptus trees. I inspected one of these on the outskirts of Perth recently and found to my astonishment that a condition of subdivision imposed by a government agency was that the developer must establish a thick belt of highly flammable eucalypts and melaleucas along the eastern edge of the new houses so as to muffle the noise from an adjacent main road and railway line. It was a classic situation where deciduous hardwoods would have performed all the desired functions of a stand of trees (summer shade, windbreak, sound proofing, even habitat to some degree) but would not have become a ghastly fire hazard in a few years time.

Similarly, I have been beating my head against the Local Government Authorities in bushfire-prone regions surrounding the city who are promoting the concept of “urban forests”, always comprising native trees. Landowners are being told to plant jarrah and sheoak (Casuarina species) trees in their front and back gardens to create a new urban forest that will counteract the impact of global warming and “save the planet”. What will actually happen is that these large trees will soon overtop the house, and will generate tons of bushfire fuel, falling into gutters and gardens, which in turn will provide the perfect recipient for burning embers from an approaching summer bushfire.

I understand that when planting non-native tree species you need to be cautious about several factors. Species must be adapted to the site, and those with a propensity to sucker or seed into nearby bushland should be avoided. Trees from the tropics need access to shallow ground water. Luckily we have plenty of experience with all sorts of exotic trees in southern WA. We know, for example that the cork oak is drought-hardy, while the silver birch (Betula pendula) prefers cooler, moister spots. Those superb beauties English oak, claret ash (Fraxinus raywoodii), London plane (Platanus acerifolia) and sweetgum (Liquidambar styraciflua) seem to grow almost anywhere in the southwest, except on the most infertile ironstones or limestone caprock. Other beauties for planting around the house without creating a bushfire hazard include Chinese elm (Ulmus parvifolia), desert ash (Ulmus parvifolia) and Judas Tree (Cercis siliquastrum). The Judas Tree is not only deciduous and non-flammable, but has gorgeous mauve blossom.

A superb spreading chestnut tree at the entry to the Foresters Wood

I often wonder why I do not see more of another of my all-time favourite trees (also a deciduous hardwood), the chestnut Castanea sativa). There is a grove of magnificent chestnuts at the entrance to the Foresters Wood, west of Manjimup which I always stop to admire when passing through, but they are almost never seen as garden or street trees in bushfire-prone areas.

Finally, as a bonus for foresters reading this story, I have included two photographs from Edlin’s book that made me smile. The first is entitled “planting Scots pine in Perthshire” and it reminded me instantly of radiata pine planting on former farmland on the slopes up out of the Blackwood River valley near Nannup fifty or more years ago. Forestry as usual was relegated to land that nobody else wanted, and the sites were so steep that the planting crew was working on its hands and knees:

The second photo captures an old-world scene, almost unknown to present day Australians, but well-recognisable to foresters over the age of about 70. The scene shows nurserymen, hand-weeding beds of open-rooted seedlings.

Nothing much unsual about this, you might say, but the seedlings in the photograph are Sitka spruce (Picea sitchensis).

I once knew Sitka spruce rather well. It grew naturally along the Olympic Peninsula in the Pacific North West of the USA, where I lived for a while in the mid-1960s, and then later I came to grips with it in plantations in Scotland. ‘Coming to grips’ with Sitka spruce was not an enjoyable experience. This species has the sharpest, most prickly and human-repelling foliage of any plant I have ever come up against, even worse than the jarrah forest’s spiny Acacia pulchella (known to bushmen as Buggery Bush). I have to wonder about those nurserymen in the picture. They must have had extremely tough hands, as none of them appear to be wearing gloves. Either that, or Sitka does not have spiny juvenile leaves (I'll have to check on this).

Old books about forestry in Britain in the years in and around WWII are unlikely to grasp the attention of many modern-day readers. But I love the insights Edlin provides into British bushfire and forest history and his profound and detailed knowledge of the trees and woodlands and their management. He writes with enthusiasm about “the skilled forester” who is applying thoughtful, site-mached silvicuture to his woods, who understands both the science and the folkore of forestry, and who has the eye of a landscape painter. His description of the beech (Fagus sylvatica) woods of southern England took me back immediately to my own adventures exploring the chalky uplands of the Chiltern Hills many years ago. I still regard the beech woodlands there as among the loveliest forests I ever saw.

Beech woodland in southern England

Incidentally, it was my view at the time, reinforced by comments from others who knew the area that the Chiltern Hills woodlands were a fine example of the “native” or natural forest of the region. Edlin has an insight into this:

… the Chiltern beechwoods, which show a remarkable inter-mixture of trees of different ages, and regenerate themselves from fallen seed quite freely, were for long believed to be truly natural. But current opinion … inclines to the view that they are the aftermath of a system of coppice manage­ment which met mediaeval demands for firewood and small poles, especially for London, to which city their produce could easily be transported down the Thames. With the increasing use of sea-borne coal in the metropolis, regular coppicing ceased, and ... these taller stems arose …

… suggesting that these lovely forests are a product of forest use and management, as much as of nature.

The other thing I like about Edlin’s book is that he provides a happy reminder of the days when forestry was a widely-admired and important profession and where working as a forest workman or as a timber worker or timber craftsman was seen as a respected and useful occupation. In Western Australia at least, those days are long gone.

References:

Chandler, W.G (1990): A forester at war. In Echoes from the Forest. Dix Print, Perth, WA

Edlin, H.L. (1956): Trees, woods and man. Collins, London

Underwood, Roger (2011): Tempered by Fire - stories from the 1961 Western Australian bushfires. York Gum Publishing, Perth WA