'Confirming Evidence' Trap: Ecological Restoration Edition Dave

It is well known among decision science practitioners that we are prone to seek evidence to confirm preconceived biases. This is one of several well-know decision traps. Government agencies are no less prone. Neither the US Congress. Enter George Wuerthner (Ecological Projects Director, Foundation for Deep Ecology) in a Jan. 18 letter to Senator Ron Wyden, arguing that thinning forests to help "restore" human-distrubed forests to functioning ecosystems may be based on flawed assumptions. Wuerthner's letter stems from Wyden's recent suggestion that he will likely introduce legislation to thin forests to "Increase Forest Health, Reduce Fires, Increase Jobs".

It will prove interesting to see whether or not Wuerthner's arguments hold sway in the Congress. And it will prove interesting to see what impact they may have on the Forest Service and/or the courts. Here, in part, is Wuerthner's argument:

Dear Senator Wyden;
18 January 2008

In light of the legislation you are considering, I wanted to make you all aware of a potentially flawed assumption about fire regimes, particularly as it applies to lower elevation ponderosa pine and also secondarily to Douglas fir and western larch. …

Most ecologists agree that stand replacement fires are the norm for mid-high elevation forests. That is, fire suppression which is thought to have influenced low elevation forest types, has not significantly altered moister forest types. That would include west side Doug fir forests, as well as higher elevation fir, spruce, and other conifer forests that dominate the Cascades, Blue Mountains and so forth. Thinning to reduce fire hazard or risk in these forests is a waste of time since when forests are ready to burn, they burn with vigor that thinning does not influence. More on that later.

However, there is a growing controversy about interpretation of fire history and the influence of fire suppression surrounding even the lower elevation drier forests. Most of the research on ponderosa pine fire dynamics has been influenced by the so-called "southwest US" model. This model has held that fires in ponderosa pine, in particular, burned very frequently and seldom experienced stand replacement or high intensity blazes. As such, many believe that fire suppression has caused these forest types, and subsequent fires in them, to be outside of the historic range of variability.

I wanted to make you aware that new research that is increasingly questioning this assumption.

For one, large blazes we are experiencing today are likely more the consequence of climatic conditions than fuels—in all forest types. And changes in fire behavior and intensity that deviate from past fire regimes such as they are understood, may be more a consequence of climatic change than anything to do with fire suppression or forestry practices—not that these are inconsequential, but that climate and fire weather (wind, drought and low humidity) may be the big driver in all large blazes.

This has big implications for what is the appropriate management response.

Secondarily recent research … has begun to question whether even the model of high frequently/low intensity blazes as typically ascribed to ponderosa pine forests is accurate.( See http://jfsp.nifc.gov/conferenceproc/Ma-01Kaufmannetal.pdf) Many of the assumptions about fire behavior and fire regimes are based on older research that is now being challenged. …

There are other recent studies confirming the same basic conclusion—the historic range of variability in ponderosa pine forests may not be as simple as often implied. Thus management prescriptions based upon this model MAY BE FLAWED.

Bear in mind that many fire history reconstructions are full of errors. …

There are other problems with past fire studies enumerated as well, not the least of which is the expectation that ponderosa pine always experienced frequent fires, thus researchers tended to find confirmation of that assumption and did not seriously critique the study methods used to reach such conclusions.

That does not mean that generalization about ponderosa pine fire regimes in the region are scientifically suspect, but at the least, one needs to review all past studies with caution and see if current characterizations of fire regimes in the area are accurate or suffer from many of the flaws outlined in the Baker paper [William L. Baker, Thomas T. Veblen, Rosemary L. Sherriff (2007) February 2007, Fire, fuels and restoration of ponderosa pine-Douglas fir forests in the Rocky Mountains, USA Journal of Biogeography 34 (2), 251–269].

I suspect that PNW and Rocky Mountains forests, particularly mixed ponderosa pine and Douglas fir/western larch forests are not as out of whack as assumed. And at the very least, what was the past condition may not be relevant to the present situation of global warming which is changing climatic conditions.

In addition there is increasing evidence that climatic conditions are the drivers of most large fires in the West. …

There are two major consequences of climatic controls on fires. The first is that the vast majority of all fires go out without burning a substantial amount of acres. That's because under most conditions, forests just don't burn all that well. These small fires seldom burn more than a hundred acres.

However, when the weather/climatic conditions are severe, almost everything will burn. The vast majority of all acreage burned in any season occurs in a few very large blazes, typically burning 50,000 acres or more, with a few reaching into the hundreds of thousands of acres. This is an important point. Our management policies, including thinning projects, are directed towards stopping or reducing the few very large fires, not the normal run of the mill fires.

However, these blazes are driven by low humidity, high temperatures, extended drought and most importantly wind. Humans can't control these factors. Notice that I did not mention fuels. It appears that under these circumstances, fires will roar through all fuels types, and even very lightly stocked stands will burn. Note that in the Biscuit Fire of 2002 very lightly stocked Jeffrey pine stands burned. These stands are naturally thinner than what you could find even in a very aggressive thinning program. Thinning might work to slow or half fires under less than severe conditions. However, under less than severe conditions, aggressive fire fighting can usually stop a blaze anyway. It is under severe conditions when fire fighting is ineffective that thinning is also ineffective.

Keep in mind that opening up a forest by thinning can actually have the opposite effect than intended. Removal of trees can increase the likelihood of a large blaze, and result in higher mortality of trees, especially during severe fire weather conditions by increasing solar insulation that dries fine fuels, and increasing wind penetration. See Hanson and Odion 2006. Fire severity in mechanically thinned forests versus unthinned forests of the Sierra Nevada, CA.

A further problem with thinning is that thinning, even where proponents suggest it is effective, will readily admit that effectiveness declines rapidly over time. Once you open the canopy up and remove competing vegetation, you encourage rapid new growth of shrubs and small trees, which are the fuels that carry a blaze. So thinning is not a one time cost, but rather an on-going long term cost that will require frequent follow up treatments. If you are not willing to continuously rethin the forest (and/or allow natural fires to burn), you have to ask how likely is it for any particular patch of timber to burn, in any particular year. Probability is actually quite low.

However, it is my view that thinning is not an effective means of reducing fire hazard under extreme fire conditions. Note that I qualify by saying extreme. Most of the evidence suggesting thinning is effective is from fires that were burning under less than extreme conditions at the time when the fire front reached the thinned sites. And for every study/observation suggesting that thinning halted or slowed fires, there are other anecdotal observations and/or studies finding that thinning were not effective in halting big fires. Typically what I find is that wind is the big factor. If wind is roaring along at 50 mph or more, no thinning is effective. If there is little or light wind than thinning may work. But again it is exactly under the conditions when there are high winds that big blazes are created and driven—so these are the fires we are concerned about. …

[D]ue to global climate change, we are seeing a shift back to a drier, warmer climate which is responsible for the larger blazes we are seeing. In a way, the occurrence of large blazes like the Biscuit Fire is perfectly normal—not an aberration. It is Nature's way of adjusting to the new climatic realities. Given these realities we can not hope to fire proof our forests. Rather the only reasonable response is for home owners and communities to take greater responsibility for reducing fire risk. Many studies have shown that fire proofing a home with metal roofs, removal of brush around a home's perimeter, etc. is far more effective for fire proofing a community than trying to thin the forest. Additionally land use zoning that keeps people from constructing homes in harm’s way is also important.

A further problem with trying to fire proof the forest by thinning is the creation of disturbance from logging operations can have many negative ecological effects including the spread of weeds to sedimentation from logging roads to the removal of large woody debris from the site. Logging is not a benign activity. Active restoration fueled by logging dollars and logging practices may in the end be worse than just allowing passive restoration to occur. (See my book on Wildfires for a good overview and refresher on the ecological differences between logging and fire). Any presumed benefit from restoration must be weighed against the impacts associated with logging—and all impacts must be accounted—and they frequently are ignored.

George Wuerthner
Ecological Projects Director
Foundation for Deep Ecology