broad-leafed, moist-leafed trees are Bushfire Retardant
We live in an age of increased bushfire risk. Broad-leafed trees such as apple, plum and pear are listed by the CFA as fire retardant trees, as opposed to many natives.
Eucalyptus and tea tree, for example, with their volatile oils (which according to law must be labelled ‘hazardous’ and ‘highly inflammable’ after extraction) are literally fire magnets.
As a blaze approaches, the oils evaporate from the leaves and infuse the heated air. These oils actually ignite in mid-air and thus jump across roads and fire breaks.
Eucalypts have evolved to spread fire. Many have bark that ignites high up in the tree and then travels quite a distance with the wind, either natural wind or a hot gale created by the fire.
It is in eucalyptus's interest as a species to attract and accelerate fire, because this promotes their germination and destroys competing vegetation. Malus, ficus, pyrus, eriobotrya and prunus, by contrast, are much harder to burn due to their high moisture content and lack of volatile oils. Trees like these have been demonstrated to slow the progress of fire across a landscape.
Australia's country roads are the ideal fire-breaks - or they would be, if recognized and treated as such. Asphalt/bitumen road surfaces can melt during extremely hot weather, but they do not actually burn. They can be considered as long strips clear of fuel; barriers against ember-attack and the spread of fire. But only if there is no way for the flames to cross the road.
Country roads thickly lined with tall, broad-leafed trees on both sides would provide the ideal fire-barrier. Flying embers caught high in their boughs would have to boil the moisture from the leaves before they could set the tree alight. By the time the leaves have dried, the embers have cooled. Embers that land beneath the trees will meet the moisture-holding, damp mulch of last year's fallen leaves, and sputter out.
Fire-bridges or fire-barriers? What do we want our country highways to be?
To quote from The Weekend Australian of February 21-22, 2009 page 9:
‘Black Saturday Disaster.
‘A former owner of the Crossways Hotel in Marysville, which survived the recent fire, Mr Lawrey, is advising residents to plant European trees around their houses rather than eucalypts.
‘”European trees saved my house,” he said. “The embers that landed in the trees had time to burn out. If they land in eucalypts they burn immediately.”
He said all three commercial buildings left standing in Marysville had European trees nearby.
‘“Of the famous oak trees lining the main street, only three will have to be removed immediately,” he said. “They really cooled the fire down when it reached them.”’
The Permaculture Research Institute
Are Eucalypts Weeds? Posted July 29, 2010 by Frank Gapinski For many years they’ve been seen as a symbol of pride in Australia. Expatriate writers in the 50s and 60s would write about returning to Sydney by ship and about being greeted by the smell of wafting gum tree leaves as they waxed lyrical about the nostalgia they felt for home. Authorities still plant them everywhere. In parks, next to footpaths, street corners, new housing development estates, Eucalypts are as Australian as the Emu and the Kangaroo. They are seen nearly everywhere and nobody seems to take them as a threat in Australia. But should Eucalypts be re-examined as a noxious weed? Supporters of Natural Sequence Farming describe Eucalypts as:
Clive Blazey , CEO of Diggers Seeds, has this to say about eucalypts : “The leaves of eucalypts hang vertically to reduce evaporation letting through light that raises soil temperatures and reduces soil moisture…by raising soil temperatures they destroy soil carbon and reduce soil fertility.
'They do more damage to our ecology than noxious weeds like blackberries, or introduced animals such as foxes” (Diggers Winter Catalogue 2009). One of the major recommendations following the Ash Wednesday (1983) fires was the planting of deciduous exotics around the perimeter of properties, due to their inherent fire-retardant characteristics.
'My final, and obvious, point is that you will go very hungry unless you begin to embrace the most important introduced plant – the fruit tree. Our future survivability in the face of chronic food shortages (another topic for another day) may well depend on that acceptance.
'We face huge challenges staying alive in tomorrow’s climate and ill-informed attitudes amounting to botanical apartheid, to quote Don Burke, can only exacerbate the situation.' Source: Do exotic trees and shrubs have a place in Beechworth? By Charlie Robinson |
TAKE THE EUCALYPT OUT OF INCENDIARY DEBATE
'The Australian' 1/1/2010 - By Robert Darby and Nick Brown THE surge in severe bushfires over the past decade has prompted much agonised soul-searching. Last year's Victoria fires led to demands to reassess a number of established practices: the leave or stay-and-defend policy; the question of controlled burning and fuel-load reduction; and the green environmental policies that have encouraged and even mandated the planting of eucalypts in rural and semi-rural areas. But if we really want to reduce the fire threat, perhaps we need to ask some even more basic questions. Is the eucalypt the right tree for rural dwellings, the urban fringe and semi-settled areas? Should we be planting more of them when climatic modelling predicts decreasing rainfall and more days of extreme weather conditions like those that whipped up infernos such as the Canberra firestorm of 2003 and the Kinglake-Marysville disaster? Should we consider planting less inflammable and more fire-resistant species instead? Eucalypts are fire-adapted, lethally so, as they are full of volatile oils that vaporise in not-so-extreme heat and explode like a bomb. On top of that they drop masses of dry bark, leaves and twigs that burn just as furiously - hot enough to melt brass taps at several metres. One lesson of history (1851, 1939, 1983 ) we seem to be taking a long time to learn is that a mature eucalypt forest is a gigantic bonfire waiting for a dry spell, a north wind and a spark. The downside of eucalypts' capacity to survive fire (or as with mountain ash their dependence on it to germinate seed) is that they also promote fires. A few years after the Canberra firestorm we took a walk in the Blue Range, an area just west of the city and in the heart of the pine forest that supplied the fuel for the blaze of January 18, 2003. The terrain had been cleared, but the site of the former Sherwood homestead was easy to find because the trees that surrounded it were alive and green. The settlers had planted oaks and elms, and although their windward side had been scorched by the flames, they were still healthy and vigorous. The area within their perimeter was untouched: a little oasis that had been protected from the blaze by a barrier of green leaves. It was a similar picture at Callignee, South Gippsland, where homesteads protected by oaks or elms survived February's fires. In contrast, many dwellings surrounded by bare lawns had been damaged or burnt by flying embers, while those near gums or pines had nearly all been destroyed. Eucalypts have been implicated in the increasing incidence and severity of wildfires in Spain, where they have been extensively planted in reafforestation projects and to provide pulp for paper production. Spanish authorities point out that the native holm oak (Quercus ilex) is fire-resistant. There are many northern hemisphere and some Australian trees that would have an equally fire-retardant effect, such as liquidambars, plane trees and poplars. Among hundreds of species of oaks, particularly those from the Mediterranean and arid regions of North America, there are several that tolerate hot, dry conditions and would thrive in many parts of southern and inland Australia. The three plantations of cork oaks on the western edge of Canberra not only survived the firestorm, but checked its advance; the stand on the northwest corner of Curtin slowed the fire and protected the homes behind, not one of which was damaged. Further up the hill, where eucalypts took over, several houses were burnt. The ACT Department of Municipal Services notes that, unlike gum trees,"Cork oak is essentially fire resistant and the foliage results in a relatively non-flammable, low-level ground fuel". As well as oaks, there are many trees originating in dry areas of the Middle East and southern Asia that would do the job - quinces, pistachios, pears and apricots, for example, and the ubiquitous peppercorn tree, once an inevitable feature of every rural homestead. Suitable native species include the kurrajong and several varieties of wattle and casuarina. Non-eucalypts offer other advantages. A plantation of wet-leaf trees is more effective as a firebreak than a strip of cleared or burnt ground, since their foliage blocks flying embers. During the Canberra fire large manchurian pears in Morehead Street, Curtin, stopped flaming embers from reaching several houses. Unlike eucalypts, whose roots release acids that limit the growth of rival plants, and whose dead leaves lie around until consumed in the next fire, leaf litter from deciduous trees rots down into compost and enriches the soil. They also moderate air temperature and increase humidity through transpiration, keeping the ground cooler and less fire-prone, and they do not desiccate soils to the same degree as thirsty gums. As the early settlers complained, gum trees are so heat-adapted they turn the edges of their leaves to the sun and give very little shade. Non-eucalypts may also offer advantages in terms of increased net carbon absorption. When calculating the effectiveness of a eucalypt plantation as a carbon sink, it is necessary to compare the quantity of carbon it absorbs during its years of growth with the quantity it releases when it burns - as, inevitably, it eventually will. We don't want to give the impression that we are advocating anything like the program of the 19th-century acclimatisation societies, which sought the wholesale replacement of native ecosystems with English trees, shrubs and fauna - though it should be that recognised Aboriginal "fire-stick farming" radically transformed the botanical profile of the continent, assisting fire-loving species to become dominant. It would be absurd to clear stretches of mountain forest and replant it with oaks. All we are suggesting is that tree-planting programs, particularly on the urban fringe and in areas where there is substantial settlement in gum forests and woodlands, consideration be given to varying the species mix by the addition of non-eucalypt varieties known for their fire-resistant properties. Local governments should particularly encourage the planting of such species on the edge of towns and around dwellings. A belt of oaks or pistachios instead of eucalypts could mean the difference between life and death in the climatic conditions that lie ahead. Nick Brown is a former high school geography teacher who grows trees near Trentham, Victoria. Robert Darby is a freelance writer and long-time Curtin (Canberra) resident. |
References:
[1] Prideaux, G. J.; Long, J. A.; Ayliffe, L. K.; Hellstrom, J. C.; Pillans, B.; Boles, W. E.; Hutchinson, M. N.; Roberts, R. G.; Cupper, M. L.; Arnold, L. J.; Devine, P. D.; Warburton, N. M. (2007-01-25). "An arid-adapted middle Pleistocene vertebrate fauna from south-central Australia". Nature 445 (7126): 422–425. doi:10.1038/nature05471. PMID 17251978. Retrieved 2011-08-26.
[2] Roberts, R. G.; Flannery, T. F.; Ayliffe, L. K.; Yoshida, H.; Olley, J. M.; Prideaux, G. J.; Laslett, G. M.; Baynes, A.; Smith, M. A.; Jones, R.; Smith, B. L. (2001-06-08). "New Ages for the Last Australian Megafauna: Continent-Wide Extinction About 46,000 Years Ago". Science 292 (5523): 1888–1892. doi:10.1126/science.1060264. PMID 11397939. Retrieved 2011-08-26.
[3] Diamond, Jared (2008-08-13). "Palaeontology: The last giant kangaroo". Nature 454 (7206): 835–836. doi:10.1038/454835a. PMID 18704074. Retrieved 2011-05-08.
[4] Turney, C. S. M.; Flannery, T. F.; Roberts, R. G.; et al. (2008-08-21). "Late-surviving megafauna in Tasmania, Australia, implicate human involvement in their extinction". Proceedings of the National Academy of Sciences of the United States of America (NAS) 105 (34): 12150–12153. doi:10.1073/pnas.0801360105. PMC 2527880. PMID 18719103. Retrieved 2011-05-08.
[5] Roberts, R.; Jacobs, Z. (October 2008). "The Lost Giants of Tasmania". Australasian Science 29 (9): 14–17. Retrieved 2011-08-26.
[6] Biello, D. (2012-03-22). "Big Kill, Not Big Chill, Finished Off Giant Kangaroos". Scientific American news. Retrieved 2012-03-25.
[7] McGlone, M. (2012-03-23). "The Hunters Did It". Science 335 (6075): 1452–1453. doi:10.1126/science.1220176. Retrieved 2012-03-25.
[8] Rule, S.; Brook, B. W.; Haberle, S. G.; Turney, C. S. M.; Kershaw, A. P. (2012-03-23). "The Aftermath of Megafaunal Extinction: Ecosystem Transformation in Pleistocene Australia". Science 335 (6075): 1483–1486. doi:10.1126/science.1214261. Retrieved 2012-03-25.
[1] Prideaux, G. J.; Long, J. A.; Ayliffe, L. K.; Hellstrom, J. C.; Pillans, B.; Boles, W. E.; Hutchinson, M. N.; Roberts, R. G.; Cupper, M. L.; Arnold, L. J.; Devine, P. D.; Warburton, N. M. (2007-01-25). "An arid-adapted middle Pleistocene vertebrate fauna from south-central Australia". Nature 445 (7126): 422–425. doi:10.1038/nature05471. PMID 17251978. Retrieved 2011-08-26.
[2] Roberts, R. G.; Flannery, T. F.; Ayliffe, L. K.; Yoshida, H.; Olley, J. M.; Prideaux, G. J.; Laslett, G. M.; Baynes, A.; Smith, M. A.; Jones, R.; Smith, B. L. (2001-06-08). "New Ages for the Last Australian Megafauna: Continent-Wide Extinction About 46,000 Years Ago". Science 292 (5523): 1888–1892. doi:10.1126/science.1060264. PMID 11397939. Retrieved 2011-08-26.
[3] Diamond, Jared (2008-08-13). "Palaeontology: The last giant kangaroo". Nature 454 (7206): 835–836. doi:10.1038/454835a. PMID 18704074. Retrieved 2011-05-08.
[4] Turney, C. S. M.; Flannery, T. F.; Roberts, R. G.; et al. (2008-08-21). "Late-surviving megafauna in Tasmania, Australia, implicate human involvement in their extinction". Proceedings of the National Academy of Sciences of the United States of America (NAS) 105 (34): 12150–12153. doi:10.1073/pnas.0801360105. PMC 2527880. PMID 18719103. Retrieved 2011-05-08.
[5] Roberts, R.; Jacobs, Z. (October 2008). "The Lost Giants of Tasmania". Australasian Science 29 (9): 14–17. Retrieved 2011-08-26.
[6] Biello, D. (2012-03-22). "Big Kill, Not Big Chill, Finished Off Giant Kangaroos". Scientific American news. Retrieved 2012-03-25.
[7] McGlone, M. (2012-03-23). "The Hunters Did It". Science 335 (6075): 1452–1453. doi:10.1126/science.1220176. Retrieved 2012-03-25.
[8] Rule, S.; Brook, B. W.; Haberle, S. G.; Turney, C. S. M.; Kershaw, A. P. (2012-03-23). "The Aftermath of Megafaunal Extinction: Ecosystem Transformation in Pleistocene Australia". Science 335 (6075): 1483–1486. doi:10.1126/science.1214261. Retrieved 2012-03-25.