Wildfire spread speed

[StringJunky]

Who is correct? This is a current dispute between a government agency and environmental group about how best to limit the spread of fires. Who has the most compelling argument?

Quote

SACRAMENTO, Calif. (AP) — Firefighters and numerous studies credit intensive forest thinning projects with helping save communities like those recently threatened near Lake Tahoe in California and Nevada, but dissent from some environmental advocacy groups is roiling the scientific community.

States in the U.S. West and the federal government each year thin thousands of acres of dense timber and carve broad swaths through the forest near remote communities, all designed to slow the spread of massive wildfires.

The projects aim to return overgrown forests to the way they were more than a century ago, when lower-intensity blazes cleared the underbrush regularly and before land managers began reflexively extinguishing every wildfire as soon as possible.

Such so-called fuel reduction efforts also include using fire to fight fire, with fires deliberately set in the cooler, wetter months to burn out dangerous fuels. Forest managers credit such burns with helping protect the Giant Forest in Sequoia National Park. The state of California eased some regulations to increase the use of that tactic.

While most scientific studies find such forest management is a valuable tool, environmental advocates say data from recent gigantic wildfires support their long-running assertion that efforts to slow wildfires have instead accelerated their spread.

The argument is fueling an already passionate debate.

It has led to a flurry of citations of dueling studies and fed competing claims that the science may be skewed by ideology.

The debate came to a head over this year’s giant Bootleg Fire in southern Oregon.

More: https://apnews.com/article/wildfires-science-business-fires-environment-a5bc4932be70d28ee408ea8102e3398c

My bias is towards the enviro position: thinning down improves the parameters for good combustion, and therefore spread.

Edited October 10, 2021 by StringJunky

[CharonY]

That is very interesting. I was under the assumption that thinning and thus removal of fuel was generally seen as beneficial. But apparently there is a huge range of answers. Depending on forest type and conditions thinning may seem to have positive or negative effects. More reading is probably needed but at first glance there does not seem to a clear answer. 

One of the caveats I read was that thinning is often not done well, resulting not only in insufficient removal of fuel, but in fact puts more fine fuels onto the ground. Also in certain areas, having less of a canopy seems to reduce overall moisture which can have retarding effects on fires.

So my guess is that what type of measures works well is likely dependent on the geography as well as the properties of the forest. So depending on these factors either of them could be right. The trick now is to isolate those factors and apply thinning only in areas where it helps. An issue of course is that changing weather patterns will also influence the outcome, so some of the older data might need to be revisited.

 

[beecee]

2 hours ago, StringJunky said:

Who is correct? This is a current dispute between a government agency and environmental group about how best to limit the spread of fires. Who has the most compelling argument?

My bias is towards the enviro position: thinning down improves the parameters for good combustion, and therefore spread.

In Australia, this is the general task undertaken in late Winter/early spring seasons, and we call it "hazard reduction burning". We have been doing it for yonks and other then when unfavourable winds blow the smoke over city areas, it is done under expert guidance to prevent it getting out of control.

 

[TheVat]

I live on the edge of wildfire country,  where there is some thinning.  I find the argument for clearing some growth fairly persuasive,  given that it does yield a western woodland closer to its natural state.   Also,  when you do have a wildfire the pre-cleared forest doesn't burn as fiercely and some tree species survive external charring quite well (trees that would be wiped out if the fire were fueled by more crowded foliage) and make a comeback.   The moisture retention approach, while it may be valid in some Eastern forests,  wouldn't seem to apply here where there is less foliage density and conditions are dryer, but it is a complex issue which can't be mastered reading a couple articles.   

Thinning can be done badly, and that's been evident here,  as when crews leave slash piles that dry out and then just go up like blowtorches when a spark lands on them.

A related issue that's come up here in the western USA is that some areas may be become dryer and hotter to the degree they no longer support a woodland ecosystem and give way to grasslands and scrub.   The only pluses to that will be it decreases the fire danger in those areas (grassfires are far more manageable) and the higher albedo of grassland will have a cooling effect.   But it also means land that retains less carbon, a shift which we really don't need right now.

Edited October 10, 2021 by TheVat

[Ken Fabian]

In my experience it isn't usually the trees that burn or that are the principle hazard, it is leaf litter and undergrowth (that will include seedling/sapling trees); it takes the right (wrong?) conditions for forest canopy fires, ie trees to burn. Reducing the undergrowth reduces opportunities for fires to find their way into canopies (laddering), although if conditions are severe enough they can do it regardless and (with Australian and I suspect SW USA vegetation) readily cross large gaps in canopy. They can also burn across areas where hazard reduction fires have been recently done. Early European explorer accounts of the area I live in cited very large, mature trees with grassy areas underneath, but these were not natural; they were the consequence of centuries of humans using fire as land management tool. After 2 centuries of tree harvesting and clearing the numbers of trees is greater, but they are smaller and with denser undergrowth.

Thinning of larger trees is probably not going to help and that is what I think of for "thinning"; others might think of it undergrowth removal I suppose.  Short term removal of trees leaves a load of dead tree tops unless those get cleaned up, which makes the exercise more difficult. Longer term the breaks in forest canopies from tree harvesting become areas of maximum undergrowth. Hazard reduction burning is done in large part because physical removal is not viable - too much of it and too much of it inaccessible. When drought has been ongoing the opportunities to do that hazard reduction burning safely is reduced. And warmer temperatures also reduce those safe opportunities.

I think raised dewpoint temperatures are critical in that; the old style light it and leave it "burning off" by Australian farmers that aped Aboriginal practices relied heavily on cool overnight conditions laying down natural fire retardant - dew and frost - that meant the fires reliably (mostly) went out by themselves. With global warming there will be less of those opportunities, ie more vigilance, labour and equipment to be safe.

[CharonY]

23 hours ago, beecee said:

In Australia, this is the general task undertaken in late Winter/early spring seasons, and we call it "hazard reduction burning". We have been doing it for yonks and other then when unfavourable winds blow the smoke over city areas, it is done under expert guidance to prevent it getting out of control.

 

There is a recent paper dealing with thinning in Australia:

Quote

Forest thinning has been proposed to reduce fire severity. However, evidence to support this strategy in Australia is scant. We completed a detailed empirical analysis of stand history data from forests burned in wildfires in 2009 in south-eastern Australia, to address the question: Does forest thinning reduce fire severity? The answer varied depending on fire type (Crown Burn vs. Crown Burn/Crown Scorch), forest type, and stand age. For the statistical relationship for Crown Burn, there were no thinning effects in ash-type forests. For mixed species forests, thinning reduced the probability of Crown Burn in young stands but increased it in older stands. Data for the fire severity category of Crown Burn/Crown Scorch revealed that thinning generally elevated fire severity, irrespective of stand age, forest type, or fire zone. Except for 20- to 40-year-old mixed species forest subject to Crown Burn, proposals for thinning to reduce fire severity have limited support.

https://doi.org/10.1111/conl.12766

[LaurieAG]

39 minutes ago, CharonY said:

There is a recent paper dealing with thinning in Australia:

https://doi.org/10.1111/conl.12766

My brothers house burnt down during the 2003 Canberra bushfires, thinning is not the issue.

https://en.wikipedia.org/wiki/2003_Canberra_bushfires

The 2003 Canberra bushfires caused severe damage to the suburbs and outer areas of Canberra, the capital city of Australia, during 18–22 January 2003. Almost 70% of the Australian Capital Territory's (ACT) pastures, pine plantations, and nature parks were severely damaged,[1] and most of the Mount Stromlo Observatory was destroyed. After burning for a week around the edges of the ACT, the fires entered the suburbs of Canberra on 18 January 2003. Over the next ten hours, four people died, over 490 were injured, and 470 homes were destroyed or severely damaged, requiring a significant relief and reconstruction effort.

Up until recently Australian state/federal governments (of all political persuasions) had adopted a policy of de funding Parks and Forest services and only 'putting out fires'.

https://en.wikipedia.org/wiki/2003_Canberra_bushfires#McLeod_Inquiry

McLeod Inquiry

...
Management of fuel load in parks and adequate access to remote areas were both lacking.
...
The Inquiry recommended there should be increased emphasis given to controlled burning as a fuel-reduction strategy, access to and training of emergency personnel in remote areas needed to be improved and a number of changes be made to the emergency services and the policies that govern their operations, including a greater emphasis on provision of information to the public.