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Wildland Fires: A Few Thoughts

I was a wildland fire fighter in California in 1951 from March first to early September when the fire season was deemed over and the seasonal help was discharged. During this time I was on the fire line for 53 large fires. Many of these were “control” burns that got out of control. The general plan was to find an area with some natural fire barriers like roads, rivers, lakes, rock slides, and rocky cliffs, or other natural barriers. The procedure was to go ahead of the fire and construct a fire line connected to barriers. Then a backfire was lit to eliminate fuel in the path of the fire. After helping to dig the fire line, my job was generally to set the back fire with a drip torch that set the fire on the fire side of the line. I would do this on the run to make sure the back fire was complete before the main fire arrived. Theoretically, the backfire would eliminate the fuel in front of the fire and stop the progress of the fire when it hit the burned over area. It was a truly awesome sight to see the main fire roaring toward us. Whole pine trees exploded into massive fire balls. The fire makes its own wind and sends burning branches flying forward. Many of these crossed our fire line and started spot fires that had to be rapidly extinguished by hand using our McCleod tool (combination of a rake and hoe), shovels, brush hooks, Pulaski tool (combination of axe and adze hoe), and backpack water sprayers. In 1954, I also did some smoke chasing in Oregon and Washington states. On one occasion I flew fire patrol with a bush pilot in the Wallowa Mountains of north eastern Oregon, U.S. looking for lighting strikes after lightning storms and calling in fire crews when necessary.  However, these fires were miniscule compared to the infernos raging today in these same areas abetted by climate change. The primary solution is to decrease the frequency and severity of wildland fires by mitigating climate change. However, another necessary step is to sustainably managing forests to reduce fire severity. This is more easily said than done as I will attempt to explain in this paper.

Basic Principles

Wildland fires require fuel (like understory plants and shrubs, downed tree trunks and branches), oxygen, heat, and a source of ignition. The composition and nature and moisture of the understory determine how much of it will burn and how intensely it will burn under the current conditions. The temperature, wind, and humidity strongly influence the fire intensity and rapidity of spread. Humans are a major source of ignition (ca. 90 percent in most cases), but lightning is also a source of ignition in many areas. It is estimated that lightning strikes the earth many thousands if not millions of times a day and these strikes have the potential to cause fires. In the more lightning prone areas like northwestern U.S., they are a major source of wildland fires. Topography also influences fire behavior and intensity. Fire moves more rapidly uphill so trying to outrun a fire uphill can be a big mistake.  There are several types of fires such as ground fires, crown fires, running crown fires, and conflagration fires (where everything ignites at the same time e.g. California manzanita- Chaparral ecosystems under high temperature and low humidity). There are various kinds of ground fires. About a third of all stored carbon is located in the northern boreal forests as the organic matter decays slowly there and massive amounts of carbon is stored in peat soils.  Ground fires can smolder there all winter, releasing greenhouse gasses like methane and CO2. 

The size of the fire also influences fire effects on the biosphere as does the amount of the forest floor removed. For example, if the forest floor is reduced down to bedrock the time for regeneration will be very long while if only some of the surface vegetation is removed the area should regenerate much more rapidly. Severe fires can change the composition and structure of the forest[1]. Conifers burn more rapidly and at a higher intensity and thus may suffer greater damage.

Climate mitigation by reducing greenhouse gas emissions is essential for reducing the frequency and size of fires. However, sustainable forest/wildland management can make a difference. Some claim that forests warm the atmosphere. However, there were lots of forests, but they did not stop the ice ages. For the last ten thousand years or so there were lots of forests, but no global warming. Some have suggested that the boreal forest should be clear cut because in the winter the whole area would be covered with snow that reflects around 90 percent of the solar heat back into the atmosphere (high albedo). However, the boreal forest is a huge reservoir of stored carbon that would be at risk under this type of management. Others have recommended we plant more trees to store more carbon in their leaves, stems, and roots and thus limit the amount of greenhouse gas in the atmosphere that holds in the solar heat. Misanthropic ecologists claim forests don’t age and that thinned forests burn more intensely than un-thinned forests. They don’t want humans to do any management of forests. Their hate speech claims that forest fires only kill 1-4 percent of the trees.  Apparently, they have never seen catastrophic wildfires like the ones that are currently raging in California.

These misanthropic claims are reportedly contradicted by experiments in the Blue Mountains of Oregon and Washington State in the United States that are using a combination of thinning and logging that appear to reduce fire intensity and result in more ground fires and less crown fires. These studies are allowing loggers and ecologists to work together[2].  Sustainable management of wildlands involves consideration of the environment[3], social aspects (including religion and culture), biodiversity[4], economics, and politics.  As the renowned German/British forester, Dietrich Brandis, explained forest policies cannot work unless the people involved agree with them. Providing jobs for the forest people gives them an incentive to maintain forests.

Trees and forests do age[5]. Part of this aging results in dead trees and downed tree trunks that increase the fuel load on the forest floor. However, decisions on managing wildlands for fire reduction are at best difficult and this is exacerbated by the changing climate. Mimicking past fire returns may not be compatible with the present circumstances. In the past wildland fires were put out as rapidly as possible. This allowed the understory fuels to build up to amounts not present in the natural wildlands and has contributed to the larger, more intense, and catastrophic fires we are currently experiencing. How much of the buildup of fuel to remove is a difficult question. Too much removal can result in damage to the soil. Too little removal can result in crown fires and/or intense ground fires that can damage tree roots and give rise to delayed mortality. Thinning and logging do remove stored carbon in the forest so a balance has to be reached, but catastrophic fires remove much more carbon and can reduce carbon sequestration for decades. There is currently a lot of modeling of the probability of fire in a given area under given conditions. This is useful, but models can only deal with a limited set of inputs while fires are a complex multitude of interacting physical and biological factors that affect wildland fires.


[1] Helen M. Poulos et al., “Differences in Leaf Physiology among Juvenile Pines and Oaks Following High Severity Wildfire in an Arizona Sky Island Mountain Range,” Forest Ecology and Management, (2020), 457: p. 117704. 

[2] W. Cornwall, “Clearing the Tinderbox,” Science, (2021), 373: p. 1300-1303.

[3] C.D Oliver and F.A Oliver, Global Resources and the Environment (Cambridge, 2018).

[4] Graeme, Berlyn, “Some Thoughts on Biodiversity and Sustainability,” Journal of Environmental Science and Public Health, (2021), 5: p. 342-344.

[5] C.D Oliver and B.C. Larson, “Forest Stand Dynamics,” Yale University E-Reserve, (1996): https://elischolar.library.yale.edu/fes_pubs/1/

CONTRIBUTOR
Graeme P. Berlyn
Graeme P. Berlyn

Graeme P. Berlyn is an E. H. Harriman Professor of Forest Management and Physiology of Trees at Yale School of the Environment.

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