References

A complete list of all references used in ‘Safer Gardens: Plant Flammability & Planning for Fire’ can be found in the book.

People living in countries other than Australia

I’ve only used results from research in other parts of the world if the plants are available in Australia. People from regions such as the Mediterranean, North Africa, New Zealand, the USA, South Africa and Brazil will find extra information about plants that are native to their area if they go online and look at the research papers I’ve used from their part of the world.

To make it easier for you to find these references I will highlight in red the country where the research was undertaken.

Here is a list of some of the main references used in the book.

Alessio et al. 2008

They looked at the influence of moisture content and monoterpenes on the flammability of Mediterranean plants in shrubland and forest in Catalonia, Spain from November to August. During this period only 50% of normal rainfall fell.

Flammability of green leaves was measured using an infrared quartz epiradiator coupled to a digital thermometer with a probe partially in contact with the leaf. They recorded the time it took for 3 phases to appear - smoke, pyrolysis and flame, commencing timing at a temperature of 60℃. They found flammability had a significant relationship with leaf moisture but few correlations were found between terpene content and flammability.

Alessio, GA, Penuelas, J, De Lillis, M and Llusia, J 2008, ‘Implications of foliar terpene content and hydration on leaf flammability of Quercus ilex and Pinus halepensis’, Plant Biology vol. 10, no. 1, pp. 123-128.

Alexander 2010

Alexander, ME 2010, ‘Surface fire spread potential in trembling aspen during summer in the Boreal Forest Region of Canada’ in The Forestry Chronicle, Mars/Avril 2010, Vol. 86, No 2.

Batista et al. 2013

They looked at the flammability of 5 plants used as green barriers in Curitiba, southern Brazil. They didn’t state what time of year their tests were carried out. They used an epiradiator set at 250℃. Samples were exposed to the epiradiator for 60 secs. If ignition took longer than 60 secs the test was considered negative. They looked at ignition time, combustion period, flame length, and moisture content. They collected green leaves and thin branches from the tops of the selected plants. They classified plants according to Valette’s system (1990). Average time to ignition ranged from 10.9 secs to 18.2 secs. Average moisture content ranged from 53.9% to 64.7%. Curitiba has warm wet summers and mild wet winters.

Batista, AC, Biondi, D, Tetto, AF, de Assuncao, R, Tres, A, Travenisk, RCC & Kovalsyki, B 2013, ‘Evaluation of the flammability of trees and shrubs used in the implementation of green barriers in southern Brazil’, In: Gonzalez-Caban, Armando, tech. coord. Proceedings of the fourth international symposium on fire economics, planning, and policy: climate change and wildfires, General Technical Report. PSW-GTR-245 (English). Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station, pp. 256-264.

Behm et al. 2004

They devised a method for creating ‘firewise’ plant lists based on observation of plant characteristics rather than on laboratory research. It was a joint product of the University of Florida Institute of Food and Agricultural Sciences, and the USDA Forest Service, Southern Research Station.

The lists compiled by the CFA in Victoria and by Sustainable Landscapes South Australia are based on adaptations of Behm et al.’s method to suit Australian conditions.

Behm, AL, Long, AJ, Monroe, MC, Randall, CK, Zipperer, WC & Hermansen-Baez, LA 2004, ‘Fire in the wildland-urban interface: Preparing a firewise plant list for WUI residents.’ Circular 145, Florida Cooperative Extension Service, University of Florida, Institute of Food and Agricultural Sciences (IFAS), and USDA Forest Service, Southern Research Station, Southern Center for Wildland-Urban Interface Research and Information, Florida.

Bellamy 1988

For his thesis Bellamy tested green leaves which he held in a gas flame in the same manner that they grew on the plant. Testing was not conducted under laboratory conditions, it was done on a verandah. He categorised plants according to how readily they burned, and how long it took for burning to stop once a leaf was taken from the flame. He also tested dry leaves which were cured on a sheltered verandah for 14 days. During this period they were exposed daily to up to 9 hours of direct sunshine.

Samples were mainly collected from the Kangaroo Creek valley area in northern NSW during late summer and early autumn. There was abundant rainfall during the sampling period. He said some deciduous plants showed signs of desiccation, indicating they were close to their autumnal leaf drop, and these plants were therefore drier than they would have been over the main fire hazard period.

Bellamy, C.A, 1988, ‘The use of plants to minimise risk of bushfire damage to buildings in the north coast region of New South Wales with particular reference to a rural area south-west of Grafton’. Thesis (Graduate Diploma of Urban & Regional Planning), University of New England, Armidale, NSW.

Bethke et al. 2016

An analysis of Californian fire-resistant plant lists.

Bethke, JA, Bell, CE, Gonzales, JG, Lima, LL, Long, AJ & McDonald, CJ. 2016, ‘Research literature review of plant flammability testing, fire-resistant plant lists and relevance of a plant flammability key for ornamental landscape plants in the Western States’, Farm and Home Advisor’s Office, University of California Cooperative Extension.

Boland 1986

Boland, DJ 1986, ‘Genetic resources and utilisation of Australian bipinnate acacias (Botrycephalae)’ pp. 26-37 in Australian acacias in developing countries, Proceedings of an international workshop held at the Forestry Training Centre, Gympie, Qld. Ed Turnbull, JW.

Brophy & Southwell 2002

They collected data from various researchers about the volatile oil content of a large number of Eucalyptus trees. Their extensive table shows that Eucalyptus trees contain volatile oils ranging from traces (less than 0.05%) to 8.6%. They said that results from single trees couldn’t be seen as representative of the species generally because wide variations in oil content can occur from tree to tree. For instance volatile oils in the leaves of Eucalyptus brookeriana ranged from 1.6% to 6.9%.

Brophy, JJ & Southwell, IA 2002, ‘Eucalyptus chemistry’ in Medicinal and aromatic plants – industrial profiles Vol 22.

Burns 1993

Burns, BR 1993 ‘Fire-induced dynamics of Araucaria Araucana-Nothofagus Antarctica forest in the Southern Andes’ in Journal of Biogeography Vol 20, No. 6, pp 669-685.

Burrows, Ward & Robinson 2001

Burrows, ND, Ward, BG & Robinson, AD 2001, ‘Bark as fuel in a moderate intensity jarrah forest fire’, CALMScience 3 (4):405-409.

Chetehouna et al. 2012

Chetehouna, K, Courty, L, Lemee, L, Garo, JP & Gillard, P 2012, ‘Experimental determination of volatile organic compounds emitted by Thymus vulgaris’, WIT Transactions on Ecology & the Environment’, Vol 158.

Conedera et al. 2010

They looked at post fire recovery of sweet chestnut, 2 deciduous oaks, and beech trees in southern Switzerland.

Conedera, M, Lucini, L, Valese, E, Ascoli, D and Pezzatti, GB 2010, ‘Fire resistance & vegetative recruitment ability of different deciduous trees species after low-to-moderate intensity surface fires in southern Switzerland’, VI International Conference on Forest Fire Research, DX. Viegas (ed).

Country Fire Authority Victoria

‘Landscaping for Bushfire: Garden Design and Plant Selection.’ CFA, Victoria, online.

The CFA no longer publishes a plant flammability list but I’ve created one from plants they use in their four online ‘low fire risk’ virtual demonstration gardens. The plants in their demonstration gardens were selected by a horticulturalist based on professional experience, then assessed using the Plant Selection Key, a method based on an American system devised by Behm et al. (2004) which has been adapted for Australian conditions. Using the Key, a plant’s flammability is assessed based on characteristics such as type of plant (eg tree), plant structure, type of leaf, type of bark, retention of dead material and volatile oil content. Their assessment is not based on flammability tests.

The Plant Selection Key automatically classifies all grasses taller than 30cm, and all climbers and vines as extremely flammable. Using this system no evergreen plant can be considered to have low flammability unless the leaves are soft, thick, succulent or fleshy. If a plant has numerous oil glands it is not considered to have low flammability. You can go online and use the Key to assess a plant’s flammability but you need to know a fair bit about the plant to do so.

CFA 2011, ‘Landscaping for bushfire: Garden design and plant selection’, Country Fire Authority Victoria.

Courty et al. 2010

Courty, L, Chetehouna, K, Garo, JP and Viegas, DX 2010, ‘A volatile organic compounds flammability approach for accelerating forest fires’, in WIT Transactions on Ecology and the Environment, Vol 137.

Dehane et al. 2017

They collected twigs with foliage from 10 species in a cork oak forest in the southern part of the Tlemcen mountains, Algeria in the fire season, September 2015. They used a mass loss calorimeter with piloted ignition for green and dry tests. They looked at ignition time, peak heat release rate, average effective heat of combustion and residual mass fraction, and measured moisture content. They describe it as a sub-humid climate.

Dehane, B, Hernando, C, Guijarro, M & Madrigal, J 2017, ‘Flammability of some companion species in cork oak (Quercus suber L.) forests’, Annals of Forest Science, vol 74.

Della Rocca et al. 2015

They investigated the flammability of the litter and green leaves of Cupressus sempervirens var. horizontalis in Valencia Spain. Material was collected in April. They used a mass loss calorimeter, an epiradiator and oxygen bomb to measure different aspects of flammability i.e. ignitibility, combustibility, consumability and sustainability. They also measured moisture content. Valencia has a Mediterranean climate.

Della Rocca, G, Hernando, C, Madrigal, J, Danti, R, Moya, J, Guijarro, M, Pecchioli, A & Moya, B 2015, ‘Possible land management uses of common cypress to reduce wildfire initiation risk: a laboratory study’, Journal of Environmental Management, vol. 159, pp 68-77.

Della Rocca, G & Danti, R 2013, ‘The role of cypress in controlling forest fires’, IPP-CNR Firenze (Florence) in The Cypress system of fire barriers: Preventive forestry, Moya, B, Moya JV & Raddiu, P (eds). Imelsa, Valencia.

Department of Fire & Emergency Services WA 2014

DFES, Department of Fire & Emergency Services WA 2014, ‘Information note: Mulch and cigarette fires’

Dibble et al. 2007

They measured the average effective heat of combustion of 42 native and invasive forest plants in the northeast of America. Time of year tested wasn’t stated. Leaves weren’t tested in their fresh green state. Using a cone calorimeter they tested samples of leaves and twigs that were dried at 60℃ to a constant weight in a drying room. They also measured time to sustained ignition, peak heat release rate and total heat release. They didn’t measure moisture content. The lowest effective heat of combustion was 8.84 and the highest was 17.73.

Dibble, A, White, R & Lebow, P 2007, ‘Combustion characteristics of north-eastern USA vegetation tested in the cone calorimeter: invasive versus non-invasive plants’, International Journal of Wildland Fire 16, pp 426-443.

Dickinson & Kirkpatrick 1985

They researched the flammability of 21 plants in the forests of south-eastern Tasmania. They collected foliage, twigs and litter in the Hobart area in winter because ‘relative calorific values should have greater reliability than in the warmer times of the year’ (p.123).

They measured rate of flame front movement, energy content, average percentage mineral ash content, and in some cases silica content. Green foliage was held in a natural position with its lowest part in a gas flame burning at constant height, and the rate of flame front movement was recorded. For some plants they also researched the effect of moisture content on the speed and extent of flame movement. Material for dry testing was oven dried at 80℃ for 24 hours. Average mineral ash content ranged from 2.4% to 10.5%.

Dickinson, KJM & Kirkpatrick, JB 1985, ‘The flammability and energy content of some important plant species and fuel components in the forests of Southeastern Tasmania’, Journal of Biogeography, vol 12, No 2 pp121-134.

Dimitrakopoulos & Papaioannou 2001

They collected mature green leaves from Mediterranean forests in summer during the hottest time of the day. They tested leaves at varying temperatures, beginning at a very low temperature, 200℃, so that they could measure low ignition temperatures which might be caused by the release of flammable volatile compounds. They used a custom built heating device that had a heating unit as well as a pilot flame. They heated the radiator cone to 700℃ and allowed it to reach temperature equilibrium. When a thermocouple placed 20cm from the radiator cone reached a set temperature of 200℃ they inserted the plant sample. After each test the set temperatures were re-established.

They tested time to ignition over a range of moisture content, drying the plants at temperatures between 28 and 32℃. They also investigated the moisture of extinction i.e. ‘the fuel moisture content at which the sample did not ignite over a heating duration of 5 minutes’ (p.147). They found moisture content was the most influential factor in plant flammability.

They tested the ignitibility of dead foliage at various moisture contents to simulate drying litter on the forest floor, but said that testing a single layer of dry foliage cannot reflect the real situation on the forest floor.

Dimitrakopoulos, AP & Papaioannou KK 2001, ‘Flammability assessment of Mediterranean forest fuels’, Fire Tech 37:143-152

Dimitrakopoulos et al. 2013

They researched the flammability of ten European conifers. They measured time to ignition of green needles using an ignition apparatus with a cone radiator. They also measured ignition temperature, heat content, and mineral ash content. Samples were collected during summer at the hottest time of the day. Mineral content varied from 2.2% to 6.1%.

Dimitrakopoulos, AP, Mitsopoulos, ID & Kaliva, A 2013, ‘Short communication. Comparing flammability traits among fire-stricken (low elevation) & non fire-stricken (high elevation) conifer forest species of Europe: a test of the Mutch hypothesis’, in Forest Systems vol 22 (1), 134-137, INIA, Instituto Nacional de Investigacion y Tecnologia Agraria y Alimentaria.

Etlinger & Beall 2004

They tested whole 2-3 year old plants from a nursery in California. Time of year tested wasn’t stated. Leaves weren’t tested in their fresh green state. They partially dried them in an oven at 50℃ for about ten hours to simulate severe water stressing. They severed the 6 plants at the soil line just before testing and placed them in an upright position in the burning enclosure. They used an ‘intermediate scale biomass calorimeter’ which had a gas flame. They investigated factors such as moisture content, surface-area-to-volume ratio, canopy volume, foliage volatiles, mineral ash content and oven-dry mass. They calculated peak heat release rate and total heat release. Mineral ash content ranged from 3% to 8%. They said mineral ash content was not a significant variable, and nor was surface-area-to volume ratio, but foliage moisture content and foliage mass were. The use of whole plants enabled them to relate heat release rate to plant characteristics.

Etlinger, MG & Beall, FC 2004, ‘Development of a laboratory protocol for fire performance of landscape plants’, University of California Forest Products Laboratory. International Journal of Wildland Fire 13: 479-488.

European and Mediterranean Plant Protection Organization 2019

Farag, El Din & Fahmy 2015

Volatile oil content in magnolias

Farag, MA, El Din, RS & Fahmy, S 2015, ‘Headspace analysis of volatile compounds coupled to chemometrics in leaves from the Magnoliaceae family’, Academy of Chemistry of Globe publications, Rec. Nat. Produ. 9:1.

Fogarty 2001

Fogarty, a New Zealand fire specialist, surveyed NZ fire managers with experience of how plants native to NZ burn in wildfires. He then assigned the plants to flammability categories and ranked them 1 to 42, with number 1 being the least flammable.

Fogarty, LG 2001, ‘A flammability guide for some common New Zealand native tree and shrub species’, Forest Research, Rotorua, in association with the New Zealand Fire Service Commission and National Rural Fire Authority, Wellington. Forest Research Bulletin no. 197, Forest and Rural Fire Scientific and Technical Series, Report no 6, 18p.

Ganteaume et al. 2012

They researched the flammability of litter from seven types of hedge in Provence, France. They tested time to ignition, ignition frequency, flaming duration, flame spread and litter bulk density. During summer they collected undisturbed leaf samples beneath hedges; these included particles from nearby species. To avoid any effect from moisture content they oven dried litter for 48 hours at 60℃. They used a glowing firebrand to ignite the samples, and a fan to replicate wind effect. Ignition times ranged from 49 secs to 188 secs.

Ganteaume, A, Jappiot, M & Lampin, C 2012, ‘Assessing the flammability of surface fuels beneath ornamental vegetation in wildland-urban interfaces in Provence (South-eastern France)’. International Journal of Wildland Fire, CSIRO Publishing, 22(3) 333-342.

Ganteaume et al. 2013

They researched the flammability of ornamental hedges in Provence, France. Green leaves were collected in summer. They tested time to ignition, time to flame extinction, ignition frequency, moisture content, mass, leaf thickness and surface-to-area volume ratio. They tested samples in an epiradiator device with a surface temperature of 420℃. The device included a pilot flame. A hood was placed over the device to prevent air currents affecting the results. They also tested the dry leaf of cypress. Ignition time of green leaves ranged from 10.7 secs to 35.5 secs. Moisture content ranged from 48% to 68%. They classified plants based on 3 variables – ignition time, ignition frequency and flaming duration. 7 species were tested.

Ganteaume, A, Jappiot, M, Lampin, C, Guijarro M & Hernando, C 2013, ‘Flammability of some ornamental species in wildland-urban interfaces in southeastern France: laboratory assessment at particle level’, Environmental Management, Springer Verlag (Germany), 2103, 52, p.467-480.

Gill & Moore 1996

CSIRO researchers Gill and Moore looked at the ignitibility of green and oven-dried leaves of Australian native plants collected in March and April. Most were from the Australian National Botanical Garden in Canberra. They recorded ignition time, moisture and mineral ash content. They tested leaves in an open muffle furnace at 400℃ using a pilot flame from a spark-gun. They placed a single leaf on a wire cradle 3.4cm above the floor of the furnace. Because of the open door there was a temperature gradient. Metered furnace temperatures averaged 398.6℃. For dry tests the green leaves were oven-dried at 95℃ for at least 22 hours.

They found that moisture content and a leaf’s surface-area-to-volume ratio explained over 80% of the variation in leaf ignition time. They didn’t test volatile oil content. Their green leaf ignition times varied from 11.6 to 57 secs. Total mineral ash content ranged from 1.9% to 10.2%. Moisture content ranged from 42.5% to 80.5%. Moisture, mineral and ignition figures are all averages.

Gill, AM & Moore, PHR 1996, ‘Ignitibility of leaves of Australian plants’, CSIRO Plant Industry, Centre for Plant Biodiversity Research, Canberra. (A contract report to the Australian Flora Foundation.)

Grace et al. 2005

Grace, J, Allain, L, Baldwin, H, Billock, A, Eddleman, W, Given, A, Jeske, C & Moss, R 2005, ‘Effects of prescribed fire in the coastal prairies of Texas’, USGS Open-File Report 2005-1287. Reston, VA: U.S. Department of the Interior; U.S. Fish and Wildlife Service, Region 2; U.S. Geological Survey. 46 p. [54491].

Groom & Lamont 2015

Groom, PK & Lamont, BB 2015, ‘Plant life of southwestern Australia: Adaptations for survival’, DeGruyter Open, Warsaw, Poland.

Henaoui et al. 2013

They researched the flammability of vegetation in the Tlemcen and Traras mountains in Algeria. They tested ignition time, duration of combustion, flame height and moisture content of green leaves. Their times for ignition were very long - maximum time was about 138 secs.

They explain their testing method as follows: ‘The samples were collected during the spring season (month of April and May 2013), a test of three samples (10g each) measured by an electric balance (1/1.000 gram) for each species was implemented using an infrared burner, wherein the temperature to start burning the samples was measured by a temperature probe of a multi-meter which corresponds to position 10 (850℃).’ (p.87). They used the method of INRA (Valette, 1990 and Moro, 2004). Valette and Moro used an epiradiator plus a pilot flame. However Henaoui et al. didn’t mention a pilot flame.

Based on ignition time in spring, 33 of the 38 plants they tested had high flammability, 4 were classed as moderate and one had low flammability. The study area has a Mediterranean climate with long, hot, dry summers.

Henaoui, SE-A, Bouazza, M & Amara, M 2013, ‘The fire risk of the plant groupings with Cistus in the area of Tlemcen (Western Algeria)’, European Scientific Journal vol 9, No 29.

Jaureguiberry, Bertone & Diaz 2011

Jaureguiberry, P, Bertone, G & Diaz, S 2011, ‘Device for the standard measurement of shoot flammability in the field’, Austral Ecology, 36: 821–829.

Kauf et al. 2014

They looked at the problem of extremely low ignition frequency when testing plant flammability. They tested the flammability of litter from eight species collected in coastal areas of Croatia in May. Only whole leaves and bigger leaf fragments from the upper leaf litter layer were sampled. Tests included ignition frequency, ignition time, ignition sustainability and temperature reached. They used a 500W epiradiator at a temperature of 420℃. They found that the temperature needed constant monitoring to keep it stable. Fluctuating temperatures could cause the ignition delay time to drop from 5.65 secs to 1.05 secs.

They expressed reservations about the usefulness of ‘hierarchical cluster analysis’ and said if too many parameters are included ‘a meaningful interpretation of the combined results will be more difficult and more of the original information on the fire behaviour of material will be lost’ (p.8).

Kauf, Z, Fanmeier, A, Rosavec, R & Španjol, Z 2014, ‘Testing vegetation flammability: The problem of extremely low ignition frequency and overall flammability score,’ in Journal of Combustion Vol 2014.

Kauf et al. 2016

Kauf’s doctoral thesis included 2 research papers which investigated the flammability of 6 Mediterranean trees in Croatia: pomegranate, carob, olive, strawberry tree, aleppo pine and holm oak. One of these papers looked at leaf litter flammability (Kauf et al. 2015). Litter samples were collected from various regions of Croatia in May, July and September/October, but there was insufficient intact litter from pomegranate trees to sample in May. Testing was done using an epiradiator at 400℃ surface temperature with a 3 gm sample. Temperature was monitored by a K-type temperature probe. The researchers tested ignition temperature, ignition delay, flame extinguish time, flame residence time and max temperature. They also looked at moisture content, specific leaf area, average area and average dry mass.

The other paper by the same 4 researchers looked at the ignitibility of the green leaves of the same 6 trees. The study examined the relationship between weather conditions (for instance drought), moisture content and the ignitibility of green leaves. Plants that had no or minimal management were selected in various regions of Croatia. Samples were collected monthly between May and October. (May, June was spring. October was autumn.) They used the same equipment and methods as in the litter study. Throughout the study period they looked at ignition delay, moisture content and also ignition frequency because flames did not appear in all the tests. They found ‘significant relationships between moisture content and both ignition frequency and ignition delay’ (p.90).

The thesis also included a 3rd paper by these researchers. See previous entry (Kauf et al. 2014).

Kauf, Z, Fanmeier, A, Rosavec, R & Španjol, Z 2015, ‘Seasonal and local differences in leaf litter flammability of six Mediterranean Tree Species’ in Environmental Management 55:687-701.

Kauf, Z 2016, ‘Testing vegetation flammability: Examining seasonal and local differences in six Mediterranean tree species’. Dissertation to acquire a doctorate in Agricultural Sciences, Institute of Landscape & Plant Ecology, University of Hohenheim.

King & Vines 1969

These CSIRO researchers tested oven dried leaves of Australian native and exotic plants, most from Queensland and Victorian forests, to see if there was a correlation between mineral ash content and flammability. Time of year wasn’t stated. Leaves were oven dried at 100℃ for 24 hours. They did 2 types of flammability tests. Firstly they observed how a dry leaf burnt when held in a bunsen flame. Then they used a radiation heater and a gas burner to test dried leaves, recording the time from first flame appearance to when the flames died out. They found a very high correlation between the visual test and the timed test. They found that in general, leaf flammability decreased as mineral ash content increased. Their percentage total mineral ash figures ranged from 2.1% to 11.1%.

King, NK & Vines RG 1969, ‘Variation in the flammability of the leaves of some Australian forest species’, CSIRO, Division of Applied Chemistry, Melbourne.

Kluge & de Beer 1984

Kluge, RL & de Beer, H 1984, ‘A.4 Silky hakea,’ Farming in South Africa, Agricultural Research Council South Africa, Weeds & Pesticides Subdivision, Plant Protection Research Institute, Weeds A.4/1984.

Krix et al. 2019

They looked at the green leaf flammability of 60 plants in the Blue Mountains (NSW). Samples were collected in the winter months, from June to August. They measured time to smoking, time to incandescence, time to flaming, smoking duration, incandescence duration, and flaming duration. They used an open muffle furnace with a temperature of 700℃ radiating from ceramic heating plates on 2 sides. They tested radiant and convective heat flow. They didn’t use an ignition device. Using the above measures they created an overall leaf flammability index, ranking plants from 1(least flammable) to 60 (most flammable). They also measured moisture content, leaf area and leaf mass per area. They didn’t test volatile oil content. A high number of plants failed to produce a flame (33 out of 60).

Krix, DW, Phillips, ML & Murray, BR 2019, ‘Relationships among leaf flammability attributes and identifying low-leaf-flammability species at the wildland-urban interface’, International Journal of Wildland Fire 28, 295-307.

Leblanc 2001

Leblanc, JW 2001, ‘Getting a handle on broom: Scotch, French, Spanish & Portuguese brooms in California’, University of California, Agriculture and Natural Resources, publication 8049.

Long et al. 2006

They looked at the flammability of ornamental shrubs in southern parts of the United States. Time of year tested wasn’t stated. They measured ignition time, flame extinction time, peak heat release rate, total energy released, maximum flame height, mass loss, plant density loss, temperatures and heat fluxes. They used cluster analysis to rank the plants’ flammability based on these measures. For time to ignition tests they used a U-shaped gas burner placed around the base of whole plants growing in containers. You can view footage of most of their ignition tests on YouTube. Their study of whole plants growing in containers enabled them to see how well flame transferred up through the plant from leaf to leaf.

Long, A, Behm, A, Zipperer, W, Hermansen, A, Maranghides, A & Mell, W 2006, ‘Quantifying and ranking the flammability of ornamental shrubs in the southern United States’, Southern Research Station USDA, US Forest Service.

Leonard & Kachel 2019

Leonard, J & Kachel, N 2019, ‘Preparing your home for bushfire’, CSIROscope webpage.

Leonard et al. 2006

Leonard, JE, Blanchi, R, White, N, Bicknell, A, Sargeant, A, Reisen, F & Cheng, M 2006, ‘Research and investigation into the performance of residential boundary fencing systems in bushfires’, CSIRO Manufacturing & Infrastructure Technology, Fire Science & Technology Laboratory, Bushfire Research.

Lubin & Shelly 1997

An analysis of Californian fire-resistant plant lists.

Lubin, DM & Shelly, JR 1997, ‘Defensible space landscaping in the urban/wildland interface: A compilation of fire performance ratings of residential landscape plants’, The University of California Forest Products Laboratory, Richmond California.

Luke, RH & McArthur 1986

Luke, RH & McArthur, AG 1986, ‘Bushfires in Australia’, Australian Government Publishing Service, Canberra. Department of Primary Industry, CSIRO Division of Forest Research.

Montgomery & Cheo 1969

They tested 6 to 8 year old plants from a Los Angeles County Arboretum field-test plot in the foothills of the San Gabriel Mountains, and from a steep hillside in the area. Green cuttings were collected in autumn in the middle of the day. Rainy season samples were simulated by immersing the cut end of dry-season samples in water for 24 hours. I’ve used the dry season (autumn) ignition results. They also tested moisture content. Ignition tests were done in a muffle furnace at 650℃. They also tested samples that were heat-dried under a heat lamp at 100℃ for 45 mins then stored in a desiccator, to assess how a plant performed with all moisture removed.

Montgomery KR & Cheo PC 1969, ‘Moisture and Salt Effects on Fire Retardance in Plants’, American Journal of Botany 56 (9): 1028-1032.

Morrison & Renwick 2000

They compared the effects of a low intensity controlled burn with the effects of a wildfire on 9 small tree species in open forest in the outer Sydney metro area.

Morrison, DA & Renwick, JA 2000, ‘Effects of variation in fire intensity on regeneration of co-occurring species of small trees in the Sydney region’ in Australian Journal of Botany, 48:71-79

Murray et al. 2013

They looked at the flammability of 52 native and 27 invasive exotic plants in dry sclerophyll forest in NSW in March and April. They tested green leaves and also leaves dried at 75℃ for 48 hours. They also looked at percentage moisture content of leaves, leaf area, specific leaf area, as well as leaf width, length and thickness.

They measured time to pyrolysis rather than time to flaming ignition, using radiant heat from an open muffle furnace at a temperature of 500℃, but they preheated the furnace to 700℃ over two hours with the door closed. Testing was done with the door open. They used a ceramic fire brick to place the sample on so that ignition would occur only due to radiant heat. The temperature of the furnace was measured with a thermocouple. They stopped the stop watch as soon as pyrolysis began because they found that not all leaves produced a flame at that temperature. They were testing plants’ reaction to radiant heat so they didn’t use an ignition device such as a pilot flame.

They said that in pilot tests few leaves ignited in an open muffle furnace at temperatures below 400℃, and if they did it took a long time. All the leaves they tested ignited at 800℃ but tended to ignite almost immediately. It was decided that 500℃ was the optimum temperature.

Green leaf time to pyrolysis ranged from a low of 6.3 secs to a maximum of 72.3 secs. Moisture content ranged from 40% to 91.6%. I haven’t used many of their results as they don’t indicate which plants have low or high flammability.

Murray, BR, Hardstaff, LK & Phillips, ML 2013, ‘Differences in leaf flammability, leaf traits and flammability-trait relationships between native and exotic plant species of dry sclerophyll forest’, PLOS ONE November 18.

Murray, BR, Brown, C, Murray, ML, Krix, DW, Martin, LJ, Hawthorne, T, Wallace, MI, Potvin, SA & Webb, JK 2020, ‘An integrated approach to identify low-flammability plant species for green firebreaks’, Fire 3(2):9.

Neyisci 2014

He tested the green leaves of 45 Mediterranean plants from the Antalya region in Turkey in the wet and the dry season, using a muffle furnace at 750℃. He didn’t mention if he used an open furnace or a spark gun. In the dry season ignition times ranged from 2.1 secs to 7.2 secs and moisture content varied from 33.8% to 72.2%. These ignition times are very short. I presume this is because he tested at a high temperature. Antalya has a Mediterranean climate with hot dry summers.

Neyisci, T 2014, ‘Mediterranean forest ecosystems, wildland fires, cypress and fire resistant forests’, 1st Thematic workshop of the MEDLAND 2020, Camerino, Italy.

Noe, Penuelas & Niinemets 2008

Noe, S, Penuelas, J & Niinemets, Ü 2008, ‘Monoterpene emissions from ornamental trees in urban areas: A case study of Barcelona, Spain’, in Plant Biology, Stuttgart Germany, Vol 10, p. 163-9.

Nord & Green 1977

The emphasis in their study was to research low growing plants with low fuel volume that could be planted to reduce fire hazard in fuelbreaks or brush-cleared areas in wildland areas of California. They ruled out most tall shrubs because of excessive fuel volume. Experimental fields were planted and testing was done at these sites over many years under natural rainfall conditions. This was a USDA Forest Service Research paper.

Nord, EC & Green LR 1977, ‘Low-volume and slow-burning vegetation for planting on clearings in California chaparral’, USDA Forest Service Research Paper PSW-124, Pacific Southwest Forest and Range Experiment Station, California.

Owens et al. (1998)

They researched the seasonal role of volatile oils in the susceptibility of ashe juniper (Juniperus ashei) to fire. They found that the monoterpene limonene in ashe juniper could increase flammability by 30% but the monoterpene bornyl acetate in ashe juniper decreased flammability. They said that the time of year when levels of monoterpenes reach a peak varies from species to species. They tested plants growing in Texas.

Owens, MK, Lin, C, Taylor, CA Jr, & Whisenant, SG 1998, ‘Seasonal patterns of plant flammability and monoterpenoid content in Juniperus ashei’, Journal of Chemical Ecology Vol 24, No 12.

Pausas et al. 2016

They tested 32 rosemary bushes in a wild population in Valencia, Spain in July, collected mid morning under sunny conditions. They tested time to ignition using an epiradiator at a temperature between 660 and 700℃ using rosemary twigs that had been hydrated to reduce variability in moisture. They analyzed the content of monoterpenes and sesquiterpenes, and looked at how the levels of terpenes influenced ease of ignition.

Pausas, JG, Alessio, GA, Moreira, B & Segarra-Moragues, JG 2016, ‘Secondary compounds enhance flammability in a Mediterranean plant’, in Oecologia 180 (1): 103-110.

Pausas, JG 2007, ‘Cork oak (Quercus suber): The roles of its bark’, Centro de Estudios Ambientales del Mediteràneo (CEAM), Paterna, Valencia Spain.

Paviour 2014

Paviour, S 2014, ‘Carbon sequestration and trading potential in semi-arid South Africa: A Karoo case study’, thesis for Master of Arts, Faculty of Arts & Social Sciences, Stellenbosch University

Philpot 1968

Philpot, CW 1968, ‘Mineral content and pyrolysis of selected plant materials’, U.S.D.A. Forest Service. Research note INT-84.

Pieterse & Cairns 1988

Pieterse, P & Cairns, A 1988, ‘The population dynamics of the weed Acacia longifolia (Fabacae) in the absence and presence of fire’, South African Forestry Journal June 1988, pp25-27.

Pompe & Vines 1966

Pompe, A & Vines, RG 1966, ‘The influence of moisture on the combustion of leaves’, Australian Forestry Vol 30, Issue 3: 231-241.

Radtke 1983

This paper focused on hillside fire risks and landscaping requirements in California, including erosion and slippage issues on steep slopes. The 2004 publication ‘A homeowner’s guide to fire and watershed management at the chaparral/urban interface’was based on this paper. Radtke spent many years researching urban-wildland interface fire and watershed issues.

Radtke, K.W.H. 1983, ‘Living more safely in the chaparral-urban interface’, Gen. Tech. Rep. GTR-PSW-067. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station, Berkeley, California; 51p.

Radtke, K 2004, ‘A homeowner’s guide to fire and watershed management at the chaparral/urban interface’, Handbook produced by the City of San Diego Water Department in cooperation with The San Diego Fire Recovery Network and The Conservation Action Committee. California, USA.

Raftoyanni & Spanos 2015

Raftoyanni, Y & Spanos, I 2015, ‘Regeneration of Abies cephalonica Loudon after a large fire in central Greece’, SEEFOR 6 (1): 5-14.

Rogstad et al 2007

Rogstad, A, DeGomez T, Hayes, C, Schalau, J, & Kelly, J 2007, ‘Comparing the ignitibility of mulch materials for a firewise landscape’, The University of Arizona Cooperative Extension, College of Agriculture & Life Sciences, September. AZ1440.

Scarff and Westoby 2006

They looked at plant characteristics which controlled leaf litter flammability in 14 tree species in Yathong Nature Reserve in NSW.

Scarff, FR & Westoby, M 2006, ‘Leaf litter flammability in some semi-arid Australian woodlands’, Functional Ecology 2006 20, 745-752.

Sheridan 1996

For her thesis Sheridan looked at the flammability of 36 common garden plants and Australian natives in and around Hobart, Tasmania. Samples were collected during summer at least 24 hours after any rainfall. She tested green foliage and oven dried foliage. The ignition source was a gas flame burning at a constant height. The green leaf was held horizontally with the leaf tip in the flame. Speed of burning was timed until the flame died out.

Her ranking of species was based on the combined findings for 12 characteristics: rate of flame front movement for green and for dry foliage, percentage moisture content, percentage ash, percentage silica-free ash, energy content, foliage density, leaf fineness, continuity of plant form, height of lowest foliage, amount of dead material retained on the plant, and bark texture. She didn’t measure volatile oil content. She commented that the flammability rankings of the 36 plants she tested would have been different if she had weighted the 12 characteristics differently.

Plants were oven dried for 3.5 hours at 105℃ for dry testing. Moisture content ranged from 47% to 91.5%. Ash content ranged from 2.1% to 13.7%. Less than half of the Australian native plants she tested had low ash content. Most plants she tested had negligible amounts of silica. The 6 plants with the lowest energy content were all exotics. The 6 ones with the highest energy content were all natives. Moisture and ash figures are averages.

Sheridan, J 1996, ‘The flammability of common garden plants and Australian natives: A search for fire retardant plants,’ thesis for Bachelor of Science with Honours, Dept of Geography & Environmental Studies, University of Tasmania.

Silva et al. 2019

Silva, JS, Nereu, M, Queiros, L, Deus, E & Fernandes, P 2019, ‘Fire hazard and plant invasions – the cases of Hakea sericea and Acacia dealbata in Portugal’, Proceedings for the 6th International Fire Behaviour & Fuels Conference, Marseille, France.

Silva, JS, Rego, F, Fernandes, P & Rigolot, E (editors) 2010, ‘Towards integrated fire management - outcomes of the European project fire paradox’, European Forest Institute Research Report 23.

Simmons, Adams & Stoner 2006

Simmons, D, Adams, R & Stoner, J 2006, ‘Fuels of the future: The challenge of new fuel types’, Bushfire Conference 2006 Brisbane, ‘Life in a fire-prone environment: Translating Science into practice’.

Srecec et al. 2017

During 2016 and 2017 Srecec et al. surveyed firefighters and others on the Croatian islands of Drvenik Mali, Solta, Brac, Hvar and Vis, about the performance of Mediterranean plant species in fires. ‘The research was based on semi-structured interviews on selected local counterparts and also in population of professional and voluntary firemen’ (p3). Their questionnaire asked islanders to rank the flammability of each plant according to whether it was less flammable (i.e. low), moderately flammable, flammable or extremely flammable. The researchers also examined photos of areas burned in forest fires. The islands have a Mediterranean climate.

Srecec, S, Kremer, D, Karlovic, K, Purgar, D and Erhatic, R 2017, ‘Possible role of carob tree (Ceratonia siliqua L.) in fire protection of agro-forest systems of Croatian south Adriatic islands regarding the similarities with other Mediterranean countries,’ Forest Ecosystems.

Sullivan 2015

Sustainable Landscapes South Australia

‘Reducing fire risk in gardens.’ The Sustainable Landscapes Project was a joint project of the Botanic Gardens of Adelaide (Department of Environment and Natural Resources), the Land Management Corporation, the Adelaide and Mt Lofty Ranges Natural Resource Management Board, and SA Water).

They looked at plants commonly grown in gardens or native to the Adelaide-Mt. Lofty area in South Australia, and classified them according to flammability traits such as plant texture and density, leaf and bark type, oil or resin content, and retention of dead material. Their classification was not based on laboratory tests. The system they used is based on one devised by American researchers Behm et al. (2004) plus the version of it used by the CFA. They consulted with landscape experts about plant characteristics. Mike Wouters, one of the team who researched and wrote the publication, provided me with extra information about some of the plants.

Sustainable Landscapes, ‘Reducing fire risk in gardens’, The Sustainable Landscapes Project: a joint project with Botanic Gardens of Adelaide (Department of Environment and Natural Resources), Land Management Corporation, Adelaide & Mt Lofty Ranges Natural Resource Management Board, SA Water. Government of South Australia. Brochure prepared by Sheryn Pitman.

Tapias et al. 2001

Tapias, R, Gil, L, Fuentes-Utrilla, P & Pardos, JA 2001, ‘Canopy seed banks in Mediterranean pines of south-eastern Spain: a comparison between Pinus Halepensis Mill., P. pinaster Ait., P. nigra Arn. and P. pinea L.’, in Journal of Ecology 89, 629-638. Anatomy, Physiology and Forest Genetics, Politechnical University of Madrid.

Tasmania Fire Service

‘Fire retardant garden plants for the urban fringe and rural areas’ by Mark Chladil & Jennifer Sheridan for the Tasmania Fire Service, 2006.

Mark Chladil told me that all the plants on the Tasmania Fire Service flammability lists have been tested by researchers. Three of their sources are Dickinson & Kirkpatrick (1985), Sheridan (1996), and Bellamy (1988). Chladil and Sheridan allocated a flammability category to each plant based on an assessment of their combined green and dry leaf performance in tests done by researchers. If tests indicated the green leaves had low flammability but the dry leaves were very flammable, they tended to give the plant a poor rating. Categories were also allocated based on knowledge of a plant’s growth characteristics, such as significant retention of dead material within the plant. They advise readers not to plant moderately flammable plants in the building protection zone.

Chladil, M and Sheridan, J 2006, ‘Fire retardant garden plants for the urban fringe and rural areas’. Tasmania Fire Service. Original research & publication supported by the Tasmanian Fire Research Fund.)

The 2009 Victorian Bushfires Royal Commission final report

The 2009 Victorian Bushfires Royal Commission final report, Volume II: Fire Preparation, Response and Recovery, Chapter 12 Planning and Building, Section 6.6.5

USDA Forest Service (USDA)

United States Department of Agriculture, Forest Service. ‘Fire Effects Information System’ (online). Provides information on the fire ecology of American forest plants, and on their distribution and occurrence, value and use. Look up individual plant names eg. black gum (Nyssa sylvatica).

Valette 1990

Valette looked at the flammability of the green leaves of forest species in France in the months May to November. He used an electric radiator with a radiant disk temperature of around 600℃ plus a pilot flame 4cm above the centre of the disk. The pilot flame and radiator were placed under a hood. When the leaf sample was placed on the radiant disk a timer was started. Time to ignition was noted when a flash occurred.

He noted time to ignition, ignition frequency, combustion duration, moisture content and combustion intensity (flame height). He used ignition time and ignition frequency to create a flammability ranking for the plants. (Summer in the French Mediterranean is from June to August, sometimes extending into September.)

Valette, JC 1990, ‘Inflammabilities of Mediterranean species’, Institue national de la Recherche Agronomique, Departement des Recherches Forestieres Laboratoire de Recherches Forestieres Méditerranéennes, Avignon, Document PIF9208.

Vèlez 1982

This paper assessed the fuel management of forests in Spain. Vèlez commented on the most effective methods of controlling fuel loads in the forest, the way fire affects different forest species, the characteristics they have developed to cope with fire, and the different types of fires that occur in various forest types. For many years he was head of the National Forest Fires Service of Spain.

Vèlez, R 1982, ‘Fire effects and fuel management in Mediterranean ecosystems in Spain’, Proceedings of the Symposium on Dynamics and Management of Mediterranean-type Ecosystems, San Diego, California. Gen. Tech. Rep. PSW-58. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, US Department of Agriculture.

Vèlez, R 1990, ‘Mediterranean forest fires: A regional perspective’, UNASYLVA 162 - Fire! Food & Agricultural Organization of the United Nations Corporate Document Repository. Forestry Department.

Weise et al. 2005

These researchers tested 10 plants from southern California over a period of a year. They measured peak heat release rate, time to ignition, effective heat of combustion, moisture content, and mass loss rate. Testing was done in a cone calorimeter using green and oven-dried foliage.

Nine of the plants came from a nursery and were well watered. They collected small branches with foliage from the outer crown then removed new growth and any fruiting or flowering parts. Plastic bags of green samples were kept in cold storage for up to one month until testing. Their highest peak heat release rate in summert was 127 (olive) and the lowest was 4 (aloe). They found that high moisture content significantly reduced heat release rates and increased time to ignition.

They also conducted intermediate-scale calorimeter tests, but the plants that they used were suffering cold weather stress, scale infection, fungal infection, and/or water stress, so I haven’t used that data.

Weise, DR, White, RH, Beall, FC & Etlinger M 2005, ‘Use of the cone calorimeter to detect seasonal differences in selected combustion characteristics of ornamental vegetation’, International Journal of Wildland Fire 14 (3).

White & Zipperer 2010

They looked at the factors that contribute to flammability and detailed the various methods researchers use to investigate plant flammability. They commented that ‘No standards or generally recognised test procedures exist for evaluating’ the 4 components of plant flammability - ignitibility, combustibility, sustainability and consumability (p213).

White, RH & Zipperer, WC 2010, ‘Testing and classification of individual plants for fire behaviour: plant selection for the wildland-urban interface’, International Journal of Wildland Fire 19:213-227.

Wyse et al. 2016

They compared the flammability of 60 common plants found in New Zealand, including some exotics. They did most flammability testing in spring or summer, but some evergreens were tested at the end of winter. Unfortunately there’s no way of knowing what season a particular plant was tested in.

Leaves weren’t tested in their fresh green state. All samples were air-dried at room temperature for 24 hours before testing because they found that most plants would not ignite if tested immediately after collection.

Wherever possible they sampled sun-exposed branches; all were healthy and showed no sign of water-stress. They collected terminal branches from most species. They used an Argentinian method for testing ‘terminal shoot’ flammability (Jaureguiberry et al. 2011). This involved placing terminal shoots on a grill that had been preheated to between 100 and 160℃, leaving them there for 2 minutes to simulate the heat effects of an advancing fire, then turning on a blowtorch for 10 seconds and measuring how easily samples ignited, how hot they got, how long they burned for, and how much of them burned. Flammability rating was based on these combined results.

The device they used enables plant architecture to be kept almost intact during testing, which they believe gives a more realistic indication of plant flammability than testing single leaves.

Wyse, SV, Perry, GLW, O’Connell, DM, Holland, PS, Wright, MJ, Hosted, CL, Whitelock, SL, Geary IJ, Maurin, KJL & Curran TJ 2016, ‘A quantitative assessment of shoot flammability for 60 tree and shrub species supports rankings based on expert opinion’, International Journal of Wildland Fire, CSIRO publishing.

Xanthopoulos et al. (2006)

Their paper is an overview of fuel management activities in European countries – mainly those with a Mediterranean climate.

Xanthopoulos, G, Caballero, D, Galante, M, Alexandrian, D, Rigolot, E & Marzano, R 2006, ‘Forest Fuels Management in Europe’, In: Andrews PL; Butler BW comps. Fuels Management – How to Measure Success: Conference Proceedings. 28-30 March 2006; Portland Oregon. Proceedings RMRS-P-41. Fort Collins, Colorado: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Zipperer et al. 2007

Zipperer, W, Long, A, Hinton, B, Maranghides, A & Mell, W 2007, ‘Mulch flammability’ in: Conference Proceedings: Emerging issues along urban-rural interfaces II: linking land-use science and society. ed Laband, DN. 192-195.

Zirogiannis (2009)

For his thesis he investigated factors that contributed to the severe 2007 wildfire season in southern Greece. The state of Elia was worst hit. Olives and grapes are its most important crops, often grown in small plots in villages or within woodlands.

Zirogiannis, N 2009, ‘Wildfire prevention & mitigation: The case of Southern Greece’. Master thesis, University of Massachusetts-Amherst

Zouhar et al. 2008

Zouhar, K, Smith, JK, Sutherland, S & Brooks, ML 2008, ‘Wildland fire in ecosystems: Fire and nonnative invasive plants’, in Gen. Tech. Rep. RMRS-GTR-42-vol. 6, USDA Forest Service, Rocky Mountain Research Station.

Zylstra (2011)

For his thesis he devised a modelling system for analysing likely fire behaviour. He also investigated the flammability of some plants in the Australia Alps. One of these tests involved measuring the ignition time of green and dry leaves from 6 plants in an open muffle furnace using a pilot flame and a thermocouple. He tested at temperatures ranging from 220℃ to 700℃. Samples were placed in the furnace when the temperature had stabilised within 10℃ of the test temperature. I’ve used the ignition results of tests at 400℃. He also measured moisture content. He didn’t state what time of year he tested plants. I used the average of his ignition and moisture results for each of the plants.

Zylstra, P 2011, ‘Forest Flammability: Modelling and managing a complex system’, thesis for a Doctor of Philosophy, School of Physical, Environmental & Mathematical Sciences, University of NSW, Australian Defence Force Academy.