The brave new world beyond the questions that we …The brave new world beyond the questions that we never asked Dr. Philip Zylstra University of Wollongong Southern jarrah forest
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The brave new world beyond the questions that we never asked Dr. Philip Zylstra University of Wollongong Southern jarrah forest 60 years unburnt
The brave new world beyond the questions that we never asked
Dr. Philip ZylstraUniversity of Wollongong
Southern jarrah forest60 years unburnt
Presenter
Presentation Notes
Relate Rod Mason’s story of Bemerangal burning at Wadbillaga. Essential elements were: Seasonal movement of people Bagal (kinship) with mattruk (Acacia dealbata) defines season of burning by the dropping of flowers Spiritual connection to landscape determines the location of the burn (near Djillagamberra mountain) Social organisation and spirituality determine the prescription weather and lighting pattern (rain men observe cloud on the head of Djillagamberra the Rainmaker, show respect with a single point ignition on a hilltop) Without sufficient respect to sit, listen and learn, English invaders would hear only the introductory notes (annual burning) and entirely misunderstand the tradition The purpose of burning was not to “clean up the bush” (only the English thought the bush was dirty) or to reduce fuels. It did however maintain a shrub layer around the campsite, providing an ongoing food source.
“The Blacks had visited the Snowy Mountains, a short time previously to us, for the purpose of getting ‘Bogongs,’ a species of moth, about an inch long, of which they are particularly
fond; to obtain them they light large fires, and the consequence was, the country throughout the whole survey was burnt…” Townsend, 1846
Tidbillaga
Presenter
Presentation Notes
This quote is frequently used to suggest that the alps were burnt regularly and broadly by the First Nations. Note however that Townsend did not see this burning being conducted, he merely attributed the effects of fire to the First Nations. In contrast, eyewitness accounts described the use of burning branches to cause moths to fall from the cave walls, rather than the lighting of bushfires in the height of summer to catch moths. Our cultural understanding of indigenous burning has been shaped by the original English conception, in which burning was a tool to change the landscape (e.g. destruction of forest to create the moors for grazing land). This is still a conception of fire as a tool of invasion. Closer attention and respect for indigenous knowledge will provide a very different perspective.
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Stem
s pe
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Acacia pentadenia
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Trimalium odoratissimum
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Bossiaea aquifolium
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LitterMcCaw WL, Neal JE, Smith RH (2002) Stand characteristics and fuel accumulation in a sequence of even-aged Karri (Eucalyptus diversicolor) stands in south-west Western Australia. For Ecol Manage 158:263–271
“Fire exclusion beyond 20 years will increase the number of trees of fire tolerant size, but this must be balanced against the fact that forest floor litter and elevated dead fuel will continue to accumulate at an approximately linear rate until stands are at least 30 years old, and at a gradually decreasing rate thereafter.”
Questions…
1. Why does elevated dead fuel plateau?
2. Why is dead fuel all that matters, and not the dense shrub layer?
71%
59%
Presenter
Presentation Notes
Why does elevated (“trash”) fuel plateau in an Olsen curve? The mechanism for the plateau is that fuel additions are matched by decomposition, but McCaw et al showed that the dense understorey had all but disappeared by 30 years (red line), so that no further additions were likely and levels can be expected to decline. A curvilinear approach better fits the data, explaining 71% of their variability, instead of 59%. The influence of live foliage on flammability is disregarded in the recommendations because the Red Book does not account for it.
“…many of my observations and comments are tentative and may
be proved wrong or subject to drastic change as more data
becomes available.” McArthur AG. Notes on fire behaviour in eucalypt forests.
Canberra, ACT; 1966
Fuel load
Presenter
Presentation Notes
The basis of fuel reduction burning in Australia is the assertion that fuel load is proportional to rate of spread. This derives from 9 data points in a 1967 leaflet by Alan McArthur. The leaflet was never subject to peer review, and McArthur described it as tentative and with potential to be proved “wrong or subject to drastic change” These 9 dots now underpin the industry, as well as being the basis for the new generation of fire simulators such as Phoenix
“…in this laboratory study, forward rate of spread was therefore found to be independent of the quantity of fuel
per unit area.”
“The lack of a relationship between headfire rate of spread and litter fuel
quantity reported in this study contrasts with widely held beliefs
within the Australian fire community and with commonly used Australian forest fire behaviour guides … which assume that spread rate is directly
related to fuel quantity.”
Neil Burrows, CALMScience (1999)
The science
Presenter
Presentation Notes
The contrast between peer-reviewed (solid lines, circled) and non peer-reviewed (broken lines) conceptions of the influence of dead surface litter on fire behaviour. When only the weight of dead surface litter is considered, both peer-reviewed models for jarrah give very close predictions of small, slow flames.
Obs
erve
d fla
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heig
ht (m
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Predicted flame height (m)
R² = 0.11
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Fuel load
R² = 0.24
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+ structure
R² = 0.80
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+ leaf traits
Presenter
Presentation Notes
Mechanistic fire behaviour modelling (https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0160715) reveals the separate influences of different forest components. Surface fuel loads maintain a low, slow-spreading ‘pilot flame’ that explains only 11% of recorded flame heights. Large flames are only possible when plants ignite, so the consideration of plant dimensions and spacing allows for the prediction of larger flames. Accuracy of predictions is however low. Consideration of leaf traits quantified plant flammability, defining the likelihood that plants will ignite, and the flam that they produce when they do. When added to the influence of surface fuels modelled using Neil Burrows’ laboratory model, consideration of plant structure and leaf traits enables the explanation of 80% of differences in flame heights.
Presenter
Presentation Notes
The Red Book and McArthur approaches therefore focus on the much less influential ‘fuel load’, ignoring the far more important dynamics of the vegetation. A focus on vegetation dynamics means that a single rule cannot be applied to all forests, but management must be informed by local ecology. This more closely resembles indigenous practices, where highly specific rules applied to fire use in different areas.
Post-disturbance
Primary forest
Partially cleared
Regrowth, or secondary forest
Northcliffe fire
Presenter
Presentation Notes
Modelled fire behaviour (flame heights) for karri forest burning on a bad January day, on flat ground, using Zylstra et al (2016). As with the other peer-reviewed approaches, the results contrast with the non-scientific approach of the Red Book. In this case however, the effects of the vegetation dynamics recorded by McCaw et al on fire behaviour have been accounted for. The post disturbance period describes the ~30 years I which fire-germinated shrubs dominate the understorey. This can be divided into the initial ‘partially cleared’ period where shrubs remain small for the initial years directly following fire, and the remaining ‘regrowth’ period of larger shrubs. Flame heights are greatest during the regrowth period. After ~20 years, the median flam height is much smaller, but occasional large and very large flames occur when the (now tall) shrubs and midstorey ignite. These do not continue into the primary forest ages, where flames are almost always smaller. Survey of the area burnt in the Northcliffe Fire found that the majority of fuel ages were ~12 years post-fire.
Question…Where are the measurements for old forests?
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Years since fire
Presenter
Presentation Notes
Studies on changing flammability with time since fire almost never measure primary forests (blue oval), but treat the regrowth as ‘long-unburnt’ Some studies define areas as young as 2-years post-fire as long unburnt, most look at areas up to 10 years some (e.g. Project Vesta) consider behaviour up to ~20 years. These ages are juxtaposed with long-term empirical measurements for a broad range of forest communities (https://onlinelibrary.wiley.com/doi/full/10.1111/aec.12594), demonstrating that in most cases, the findings would not have detected the decline in mature forest flammability. By ignoring the evidence from mature forests that could falsify existing beliefs, the current knowledge base underpinning prescribed burning is fundamentally flawed
Presenter
Presentation Notes
Leverage is the measurement of annual wildfire area burnt as a function of the area within the partially cleared stage of regeneration (red arrows and lines). As with the other approaches, regrowth forest is treated as if it is mature forest, despite having been initiated by the fire. As a result, the flammability of “long-unburnt” forest is exaggerated, biasing leverage to report positive feedbacks (mature forest less flammable than post-disturbance forests) as negative feedbacks (flammability increases over time) If forests were divided into post-disturbance and primary stages (blue arrows and lines) positive feedbacks could be correctly identified.
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odel
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Presenter
Presentation Notes
Southern tablelands dry sclerophyll forest dynamics were measured across a range of ages post prescribed-fire Near-surface vegetation (e.g. grass tussocks) regained height very quickly (centre top graph) Shrubs took longer to regrow (centre graph), and consistently thinned over time (centre bottom graph) Modelling using Zylstra et al (2016) that accounted for these changes over time (bottom right graph) produced the same positive feedback and very similar characteristics to the empirically measured trend (top right graph) from Zylstra (2018).
Southern jarrah forest60 years unburnt
How might we think of fire if…
• We didn’t try to fit fire knowledge from the First Nations into our existing plans, but let it speak for itself ?
• We only used peer-reviewed fire behaviour science?
• We measured mature forests instead of just regrowth?
Presenter
Presentation Notes
Listening to First Nations knowledge means that instead of attempts to fit their techniques into our existing priorities such as hectare targets, asset protection or maintenance of timber/grazing resources, we listen to their priorities which may be very different. Doing this represents a move away from an invasion mindset. Fire management involves life and death decisions – for people as well as for other species and ecosystems. In any other field where this is true (e.g. medicine), we would expect peer-reviewed science as the basis. Dependence on such approaches when science is available opens managers to concerns about duty of care. We cannot know empirically whether prescribed burning is reducing fire risk or increasing it until we measure primary forests.
Thanks to
• Rod Mason, Alice Williams, Wayne Webb and other indigenous teachers
• University of Wollongong Centre for Environmental Risk Management of Bushfires
