Article of the Month - April, 2009

Managing Forest Fire Hazards. by Ron Mahoney.

Fire has certainly been in the news in recent years, even in eastern forests in Georgia and Virginia, where we don’t usually think of large forest fires happening. In Idaho, and other western states, where large wildfires are increasingly common, rural landowners often think that fire is something that happens to other people in other places.

With wildfire getting a lot of attention, some forest owners are taking steps to reduce their fire hazards.  A lot of this activity is centered on protecting homes and their immediate surroundings, but another focus is on forest properties with or without homes.  Most of us know about the “fire triangle”: fuel + heat + oxygen = fire.  We can’t do much about oxygen, but we can manage forests to reduce both fuels and heat. Basically, heat increases with both the continuity and composition of fuels, so fuels — anything in the forest that can burn— are the key to reducing fire hazards.

A forest stand with high fuel hazard index.
Photo by Eric Sjoquist.

Much has been written and said about the increasing fire risk of over-dense forests due to a century or so of fire suppression.  The result has been a focus on thinning forests to reduce fire hazards, and this is one part of fuels management.  But, what happens when we reduce the overstory tree density in most Idaho forests? More trees reproduce and shrubs increase in density and height and other ground vegetation (grasses and forbs) flourishes. In many situations, this can create an even greater fire hazard than dense trees alone.  When fire begins to “crown out” or burn from tree top to tree top, it creates intense heat from volatile foliage, especially in conifers. Crown fires can move at tremendous speeds and leap fire barriers such as roads, streams, or fire lines.  Ground fires, in contrast, usually move slower and are less likely to cross barriers.  While dense forests with little understory can have crown fires, without the “fire ladders” that shrubs and understory trees provide, crown fires are less likely to develop.  Consequently, fire hazard is initially reduced when dense forests are thinned and the thinnings are removed, slashed, or mulched.  Subsequently, in as little as 3-5 years, regrowth in the understory can bring the fire hazard back near or even beyond the original risk of a catastrophic burn. Most vegetation in the inland northwest is adapted to fire and other disturbance and either resprouts after fire or cutting, regrows from underground roots or bulbs, or has an abundance of light seeds that quickly establish on disturbed sites.  Similar conditions are created when forests are “thinned” by insect or disease outbreaks or weather, with even greater hazard because dead trees burn hotter, and are more likely to fall or break and become fire ladders.  The obvious solution is regular and repeated re-treatment to maintain the desired fuel conditions. 

A forest stand after machine mastication fuels treatment.
Photo by Eric Sjoquist.

Fuel conditions can be a complex and variable situation to manage Recent research at the University of Idaho addressed the retreatment of forests that had been initially treated with some overstory thinning over a period of years, and then mechanically treated with a machine that masticated all ground vegetation.  Our partners in this research, the Coeur d’Alene Tribe and the Kootenai County Emergency Planning Committee, were interesting in the effectiveness and cost efficiency of alternative retreatments on these Tribal forests in northern Idaho, three years after the initial fire hazard reduction treatments. They asked us to investigate four alternatives: mechanical (machine mastication), hand treatment (saws, mowers, brush cutters etc.), herbicides, and goat browsing.  Initially, the study intended to include prescribed burning, but weather and regulations conspired to keep us from implementing fire, and in fact this management tool is unfortunately often limited for these reasons.

The study was done on a grand fir habitat type, which is a mid-range moisture/productivity habitat that characterizes much of the lower to mid-elevation lands of central and northern Idaho. UI Graduate student Erik Sjoquist conducted this study, and in the course of his investigation, he developed a new way to describe fire risk that he calls “Fuel Hazard Index”, which is a combination of standard risk ratings that estimated the likelihood of crown fire developing.  Erik also assessed the cost per acre of each of the four alternatives, so that his results included not only how well each method reduced vegetative fuels, but also how economical each was. He measured the results immediately after treatment and again one year later.  Erik concluded that the combination of the herbicide treatment and subsequent mechanical mastication would be the most effective and affordable.  The herbicides were targeted at shrub species that were the most dominant and effectively killed them.  However, this often left dense standing dead stems, with unknown fire hazard.  Subsequent machine mastication removed these stems and other standing ground fuels, leaving a mulch-like layer that gradually decomposed, is less likely to ignite, and doesn’t provide fire ladders.  Because the targeted shrubs were killed, they could not resprout. The hand treatment was very effective, and was especially good at removing ground vegetation closer to trees than the machine could.  However, the hand treatment was very expensive and deemed not worth the extra cost vs. machine treatment.  The goat treatment looked effective immediately afterwards, but by the following year, there was no measurable effect compared to the non-treated control sites. The goats were fenced and allowed to browse for a limited time, several weeks. Although longer or repeated goat browsing would undoubtedly be more effective, this alternative was also very expensive and unlikely to be cost effective unless integrated with some enterprise utilizing goat milk, meat, hides, or a combination of these products. This study also compared all treatments to sites that had never been treated and to initially treated but not retreated sites. Consequently, the study concluded that a reasonable retreatment cycle would be about five years. 

Condition of foreground vegetation two years after machine treatment; background vegetation not treated.
Photo by Eric Sjoquist.

The Coeur d’Alene Tribe was also interested in the wildlife habitat implications of this fuels management research. They asked the University to expand this research to look at general wildlife habitat impacts, and more specifically the influence of fuels retreatment on forage quantity and quality for deer and elk. A UI graduate student began this wildlife habitat impact study as Karen Neorr and ended it as Karen Sjoquist, an unplanned but delightful consequence of meeting Erik Sjoquist during this research.  Karen investigated general wildlife habitat components one and two years after the fuels retreatments were initiated in Erik’s study, and concluded that these practices had no lasting impact on wildlife habitat other than to diversify the vertical structure of the forest, which is generally considered a habitat improvement.  She also did a more specific investigation of the quantity and quality of forage for deer and elk on these research sites. The machine and hand mechanical alternatives obviously caused an immediate reduction in forage quantity, as did the goat retreatment to a lesser degree. The herbicide application targeted shrub species that are less desirable for deer and elk, particularly when these shrubs are older and woodier before treatment. Herbicide use had little initial impact but later increased the amount of palatable forage, so had some beneficial effect on forage quantity. The goats ate only the leaves, and resprouting occurred later in the summer, and by the next year, fuels were unaffected and desirable forb and grass forage was reduced. The machine and hand mechanical sites had improved forage quantity of some palatable plant species after the first and second year following treatment, and tended to shift the vegetation compositions towards more grasses and forbs which are favorable for deer and elk summer range.  The forage quality investigation was based on coarse fiber (less fiber is good for deer and elk forage) and protein content. The first year after the retreatments were implemented, fiber was reduced and protein was increased, providing a more nutritious forage base. By the second year, for the mechanical treatments, fiber and protein content reverted to pre-treatment levels.  Karen concluded in her recently completed thesis that vegetation treatments to reduce fire risk do not negatively impact wildlife habitat and can provide some short and long term improvements. She also recommended that the combination of herbicides and machine mechanical treatments found by Erik to be an affordable effective fire hazard reduction strategy can be acceptable for wildlife and even improve some aspects of forage for deer and elk.

These studies are a valuable window into the complexities of managing forests to reduce fire risk and the negative impacts of wildfire if ignition occurs.  They improve our ability to make informed decisions about how and why we manage forests to reduce the likelihood and negative impacts of fire in the forest.  Although wildlife habitat and other environmental considerations are more complex issues than this limited investigation can fully address, this research does provide some immediate wildlife and fire hazard management information.  I hope this article provides some stimulation for you to take a more intense look at the forests you use and perhaps own, as well as some advice about managing fire risk and wildlife habitat.

Soon, there will be a new website called the “Wildfire Information Network”.  By this time next year, you will be able to do an internet search on this title, or on many aspects of wildfire, and get the web address to access the website. The website is a product of the Cooperative Extension System’s move towards computerized education.  You can search the title “eXtension” now and get access to lots of other topics of interest to landowners, including horses, pasture management, other natural resources issues and topics, and lots of other information on homes, people, finances, and the environment.  When the new website is up and running sometime in September 2009, you can access publications and lots of answers to questions about the topic of this article.