Defending Against Fire, Guarding Against Erosion

Firebreaks are a cornerstone of wildfire prevention, providing a defensible position if (and when) a wildfire occurs. Historically, most firebreaks and land clearing were done with a bulldozer, a method that: “…nearly always destroys the topsoil…” according to a technical paper posted by the Virginia Cooperative Extension (Options for Clearing Land: Pasture Establishment for Horses, by Porr, Childs, and Downing).

Conversely, a relatively new method of creating firebreaks, mastication, which involves grinding the vegetation in place and leaving it on the ground as mulch, is perhaps the most effective way to reduce the risk of wildfire and minimize subsequent erosion. Along the way, it can actually protect and enhance the soil.

In this age of environmental concern and life cycle analysis, decision-makers must balance all aspects of what they do-even when it comes to the vital issue of fire control.

And the stakes are being raised. According to a 2008 summary by Cal Fire (formerly the California Department of Forestry), the damage (in dollars) of wildfires in California has increased dramatically over the past two decades, in some years reaching nearly $1 billion. Estimates by others set the loss even higher. The bottom line is that fire prevention efforts continue to increase.

Many leaders are facing the difficult task of reducing the risk of wildfire while minimizing other collateral damage such as erosion and air pollution. To that end, the application of new techniques will prove to be an important survival skill.

But first, let’s talk generalities in regard to firebreaks: why we need them and how they work.

Flame Length
An advancing wildfire, in high grass, for example, can have a flame length of a few feet. Flame length is the distance from the fuel source (i.e., grass) to the tip of the flame. In heavy brush, flame length can reach 30-40 feet, and in very heavy vegetation with heavy winds and a steep slope, flame length can exceed 100 feet.

For a firebreak to be effective, it must be wide enough that burning vegetation will not cross the line, and also that the heat emitted by the advancing fire will not ignite material on the other side.

There are actually many criteria used to determine the minimum width of firebreak required, including height, density and type of vegetation, moisture content, wind speed and direction, and topography-mostly related to slope.

One rule of thumb, according to a technical paper by Texas A&M University Cooperative Extension, states that “…the width of the fireguard should be at least three times the height of the adjacent vegetation.” But, of course, the other criteria must also be factored into the equation.

Several types of firebreaks are used, each providing its one level of effectiveness and collateral damage. Here’s a quick rundown of some of the most common ones.

Dozer Firebreak-Historically, these have been massive perimeters-from 1 to 10 or more dozer blades wide-where vegetation is removed and the firebreak is stripped down to mineral earth. Topsoil and all humus/organics are pushed into windrows or piles to create an absolute barrier to fire advance. From the standpoint of a positive firebreak, this method is the most definitive: No fuel equals no fire.

On the downside, this method creates a significant scar on the landscape and considerable remediation is often required to mitigate other environmental concerns.

Controlled Burn Firebreak-Controlled burns, when carefully monitored by a local fire department can also provide an effective firebreak. This method is less disruptive than a bulldozer firebreak, but has the drawback of creating a massive amount of smoke. One acre of chaparral brush can produce up to 29,000 pounds of carbon dioxide, along with lots of smoke and particulate matter 10 micrometers or less in diameter (PM10)-a major health/air quality concern. Controlled burns, still widely used in rural areas are becoming much less popular in urban-interface areas-for obvious reasons.

Blackline Firebreaks-Blackline firebreaks, where all vegetation is burned between two narrow, parallel firebreaks offers somewhat of a compromise. Blacklines can provide wide firebreaks, with much less soil disturbance than full-width bulldozing. And, when bulldozed vegetation is drifted to the inside, it may be burned along with the centerline strip. Blacklines provide wider firebreak with less damage-but still produce a considerable amount of smoke.

Hand Clearing-Some firebreaks must be done by hand because of steepness, or the presence of rocks or other obstructions. While it can be effective, hand clearing can be time consuming…and just plain hard work. And in many cases, there will be piles to burn.

Mastication
A more environmentally sensitive alternative-recently gaining wide acceptance in the world of fuel reduction-is mechanical mastication. This method uses a mastication head-essentially a wood chipper or grinder mounted on a tractor or excavator.

Mastication heads come in a wide range of widths, from a 3-foot-wide head designed for use on an excavator to units up to 8 feet wide designed to mount on very large tractors.

The most common are 5-6 feet wide and mounted on compact track loaders (tracked skid-steers). These are formidable machines in the 100-horsepower range, often weighing more than 6 tons.

Mastication heads also vary in type. Most have carbide teeth that break up vegetation by grinding it against the soil. Other, more specialized mastication heads use rotating knives to actually chip the material against a metal cutter bar inside the head-just like a mobile wood chipper. The latter provides mulch with a finer particle size, with little or no impact to the soil surface.

Mechanical mastication is becoming more widely accepted as a means of providing an environmentally friendly means of fuel reduction. In a recent report, the US Forest Service stated that, “on a per-unit-area-affected basis, wildfire is predicted to produce nearly 70 times as much sediment as a thinning treatment [i.e., such as mastication].”

Similarly, when it comes to air quality and the release of greenhouse gases such as carbon dioxide, the initial process of mastication produces 99% less carbon dioxide than burning (i.e., during a controlled burn).

While mastication does not provide the absolute firebreak that bare soil does, in-place mastication provides a viable alternative. By reducing thick vegetation and small trees to a layer of mulch, flame length can be reduced to inches and an advancing fire’s speed can be slowed to a crawl.

In sensitive habitats, where soil disturbance must be minimized, mastication can actually be accomplished with rubber-tracked machines.  With the right equipment, there is virtually no soil disturbance.

Masticating heads can also be mounted on “spider” excavators, machines that look more like crabs than excavators.  This equipment can work on very steep terrain, clearing vegetation on slopes that would otherwise be inaccessible.

Cost of Mastication
The previously mentioned Virginia Cooperative Extension technical paper also stated that: “…mulching fees can start anywhere from $200 to $400 per hour … and though larger equipment costs more [up to $1,200 per hour], it also works faster.” Depending on site-specific conditions, the study also found mulching to be about half the cost of conventional clearing. They found that production rates, including those for very large machines, could range from 1 to 8 acres per day.

A typical (mid-size) masticating machine can achieve production rates of 2 to 3 acres per day and translates into a cost of $500 to $1,600 per acre.

This may seem slow and expensive compared with building firebreaks with a dozer, except when you consider that, when masticating, at the end of the day those 2-3 acres are cleared, mulched…and done.

As pressures to prevent and control wildfires push one way-and air quality and erosion concerns push the other-leaders are being put into a double bind. This is often more serious than simply trying to keep residents happy. In many cases, solving one issue can lead to regulatory violations somewhere else.

Mechanical mastication can provide a means of directing those pressures toward a solution where everything works and all related agencies are united…and happy.