On Wildfire

July 17, 2021 (top) and same date previous year (bottom); photo courtesy BJ Swanson

Wildfire season in the Western U.S. is off to an early and strong start this year. I hear from many folks that certain regions are up to six weeks earlier than average. So what are the major factors in timing and severity of these natural (design feature) events? And how should we think about fire as dominion-takers, garden-tenders, and fire-makers ourselves? Future articles will be dedicated to pointing out the many plants, animals, and ecosystem processes that rely on periodic fire, discussion of the challenges of understanding longitudinal fire data, prescribed burns, and more. 

Many ecosystems in the temperate zones of the world burn regularly. Depending on the type of climate, topography, and resulting vegetation, some places see fire more often than others. For example, the long-leaf pine ecosystems of the Southeast, like the loblolly pine forests of the Carolinas, see short period fire regimes or fire return intervals. These areas burn more frequently but with lower intensity. This inverse relationship is a good rule of thumb. The more frequent the fire in an area, the tendency for the fire to be less severe. These short interval fires tend to not be “stand-replacing” but are more often ground or forest understory fires.  

Longleaf pine, copyright Colin May

Use this fire regime table to find out the fire interval and severity in your home and nearby ecosystems. 

Like all things ecological, wildfire’s impact on the landscape and its plants, animals, water, and soil is complicated. A good friend’s recent thoughtful question helps to unpack these relationships. He asked:  Isn’t the Sand Mountain Fire (Latah County, Idaho, 2021, part of the the Leland Complex Fire) in a managed forestland? I keep reading “heavily forested” and “dense trees”…is this forest not being thinned?

This question is super helpful because it identifies forest management practices as playing an important role in fire ecology. They certainly do. There is an oversimplification out there that the greater the fuel load the more severe the fire. Following this logic, the more “fuel” we remove via logging, road-building, prescribed burning, the less likely and less severe the fire. 

The Palouse Ranger District (Nez Perce-Clearwater National Forest), where this fire continues to burn, is probably the most heavily managed (thinned, recreation, road-building) National Forest land in all of North Idaho. So, why is the Sand Mountain Fire burning? According to our logic above, the 2000+ acre fire should have been simple to contain or even ideally would have burned itself out of fuel before growing to this size.

Fire needs three things: fuel, oxygen, and an ignition source

Fuel should be broken up into at least 2 categories: fine fuels (needed to start fires) and coarse woody debris (downed trees, standing dead). These fuels are further broken down into size classes (diameter of fuel) and organized by the time required to fully dry this fuel, if live at time of fire onset (see graphic). We could definitely distinguish other features such as the thickness of the duff layer as important, but we will limit ourselves to these two for now.

A fire gets going because of fine fuel, wind (oxygen), and a spark. And so a forest that is dry, has fine fuel, and a spark will lead to fire. Thinning can help reduce risk of a fire moving if the fire stays on the ground and there is no wind. However, thinning can also increase the chance of fire. Removing trees (especially larger ones) dries out the forest as moisture trapped by a forest canopy and understory now lies exposed and evaporates.

Coarse scale view of forestland checkerboard ownership and management matrix
Finer scale view of same forestland east and around Sand Mountain Fire.






When news folks talk about dense forest and this particular fire there has been some information lost in translation. Many landscapes have a patchy matrix, especially those close to towns or with a significant number of rural residents. Much of the Western US that is forestland managed by the US Forest Service exists in a shockingly regular checkerboard pattern. This pattern reflects mixed-ownership (private, state, federal) and mixed-management.  There are some areas of dense trees and other areas of clearcut and other areas of thinned forest. There are also meadows and creek and river valleys of various vegetation types. In today’s climate and especially this year (dry spring) any and all of this will burn given the three primary ingredients: fine fuel, wind, spark. And so bottom line, fire is not a result of management (good or bad) necessarily, it is primarily a result of climate. 

These fires, like most forest fires (not grassland or shrubland fires) were caused by a series of lightning strikes. Where lightning strikes, like where wildfires occur, is almost completely unpredictable. And so preventative management of forestland is incredibly difficult.

With this much variability on the landscape is it honest to say that any given fire season is typical or atypical? Or a better question, what does the current pattern of wildfire look like in an historical context? These questions and their answers have political and economic ramifications. I hope to provide clarity here in future installments. 

An important starting place for addressing most of these questions center on the question, “Is this forest healthy? Some officials and industry folks want particular forests deemed unhealthy so that certain management practices may be put into place that “heal them.” Other officials and ecologists want to deem the same forests healthy to reduce these management efforts or perhaps to employ different management techniques.

And so how is this ambiguous term, forest health defined?

The USFS defines forest health as the production of forest conditions which directly satisfy human needs and by resilience, recurrence, persistence, and biophysical processes which lead to sustainable ecological conditions. 

The Journal of Sustainable Forestry defines forest health more simply but then adds some important next steps: If forest health is to be approached scientifically, it must be defined and measured. Forest health is a condition of forest ecosystems that sustains their complexity while providing for human needs. We developed this broad definition because a wisely acceptable definition is lacking, and forest health is a focal point in discussions of how to sustain forest ecosystems in the United States. Steps for measuring forest health are: (1) select a representative set of indicators for a particular ecosystem; (2) establish baseline data, such as a historical range of variability; (3) develop standards against which to compare current conditions; and (4) establish a monitoring program to assess current conditions and modify baseline data as new trends develop.

Photo point for the 1988 Yellowstone Fire. Regrowth and pond in the same location in 1989, one year later. NPS/Jim Peaco

I like the second definition because of its simplicity. And I agree that certain indicators should be chosen and they should be chosen based on their importance to the ecological integrity of the ecosystem of study. For example: water temperature, turbidity, dissolved oxygen, thickness of duff layer.  By defining forest health creationally (biblically, wisely, in the context of fire being a design feature and important for many creatures and ecosystem processes) we can avoid relying on poorly collected or contested fire data of the past (of which there is much). More importantly this puts us in a position to see fire not only as “devastating,” which it can be, but also as restorative and essential

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