Carlton Britton
Introduction
The prescribed burning program at Texas Tech University began the day Dr. Henry A. Wright was hired in 1967, and this manuscript is dedicated to his memory. I would like to emphasize what you already know; rangeland burning would still be an infant art without Henry’s drive, determination, and foresight. He broke a multitude of seemingly impervious barriers, allowing the rest of us to rush into this massive void in range management.
Historical Perspective
Prescribed burning of juniper communities started with a phone call from Mr. Bob Beckham of Abilene, Texas. Bob had heard of Henry’s fire research and wanted to know if burning would work on his ranch south of Baird, Texas. Henry’s answer was, “Of course, it will work. I will send Carlton down to look it over.” Thus began one of the great adventures as we plunged unknowingly into a spring of constant work, frustration, and learning from a multitude of mistakes. The road to success would have been extremely difficult without the unflinching support of Bob Beckham.
Bob Beckham had a typical juniper problem seen throughout central Texas and the Edwards Plateau. Ashe juniper was so thick that a cow could not walk through it, and there was no grass in the understory. He had bought a dozer and was in the process of pushing individual trees into huge piles. The volume of material was unbelievable and Bob was interested in using fire to rid his pastures of this juniper debris.
I made the first, and a critical, mistake when I first visited the Beckham Ranch. However, this mistake was to cause a pivotal change in the direction of the fire program at Texas Tech. I was overwhelmed by the volume of juniper debris. Knowing the excessive flame lengths this would produce, I advised Bob to push the debris back 100 feet, which would give a wide and clean fire line. This process proved very expensive and created a windrow of debris capable of producing millions of firebrands and lifting them to heights that could be carried well over a 1,000 feet down wind igniting spot fires in the next pasture. Solving this mistake resulted in many hours of hard work and forever changed the way firelines were prepared. These windrows could only be ignited at night when the temperatures were cold, humidities were high, and winds very calm.
Early one morning, as we were leaving the Beckham Ranch, Henry asked me if I had noticed how differently the fires burned when the humidity rose to over 40%. Of course, I said, “No,” since I was generally scared stiff looking for and putting out spot fires. Henry persisted in his theory that 40% was an important breaking point in fire behavior, and we all began to notice these differences and rely on this threshold point. Later under Henry’s guidance, Steve Bunting clearly defined a similar threshold value for temperature.
After finally burning Bob Beckham’s pasture, we knew that firebrands were the main source of our problems. As the grass greened, Henry located several west Texas ranches with piled brush, and we started a study to determine how far firebrands traveled. The hypothesis was that the size of the pile was the primary factor in determining how far a firebrand would travel. Thin plastic was placed at several distances down wind of each juniper pile and the pile ignited. When the pile was consumed, the plastic was inspected, and the distance to the furthest piece of plastic with holes was measured. It was obvious that the pile size was correlated with distance traveled by firebrands. However, it was also obvious that other factors were important.
Steve Bunting’s arrival marked the next series of important fire research. Steve’s thesis research concerned a more critical evaluation of firebrands. Henry and Steve solved the problem of firebrand ignition potential. Their research established that below 70F firebrands had a greatly diminished potential to ignite spot fires. This finalized what has become known at the “40 – 60 rule.” Simply stated, firebrands have a minimal potential to ignite spot fires when the relative humidity is above 40%, air temperature is below 60F and wind is less than 8 mph. This rule has been tested over 25 years and in most rangeland fuels across the nation, and it is just as valid today as when it was first stated.
The fire program picked up momentum and diversity during the 1970’s with the help of one of Henry’s Ph.D. students, Dr. Leon Neuenschwander. Leon directed to Henry two exceptional students, Dr. Al Steuter, now with the Nature Conservancy in Nebraska, and Dr. Guy McPherson, now at the University of Arizona.
Al Steuter was the graduate student fire boss during the mid to late 1970’s and contributed greatly to the transition from burning Ashe juniper to the more difficult use of fire in redberry juniper. The primary difference in the two communities is the lack of fine fuel found in the redberry juniper type of the Rolling Red Plains of Texas. The roughness of the terrain in the redberry juniper type appreciably confounded this lack of fine fuel. The 500 foot blackline was firmly established as the standard fireline during this period. This fireline was burned using the 40 – 60 rule, and, with the prevailing southwest winds of the region, was always placed on the north and east side of the unit to be burned. This black line provides the necessary fuelless barrier to stop the head fire used to burn the main portion of the pasture.
As the fire program moved into the 1980’s, two additional innovative practices were adopted. The first was the use of strip headfiring of blacklines and the intense organization of fire crews. This innovation was perfected by an unusual group of graduate student which were both intelligent and highly motivated. This group consisted of Guy McPherson, Bob Masters, Al Rasmussen, and Jeff Weigel. This group was assisted by the constant and energetic work of Gretchen Scott. This era saw the first preparation of fire plans for each burn. These plans included a detailed description of the burn unit, conditions for blackline and headfire ignition, and maps of the terrain with potential trouble spots. These plans made the dissemination of information to all crew participants very easy and complete.
This period in the fire program saw another extremely valuable development. A high level of organization was developed for conducting prescribed burns. The basic prescriptions had been developed and tested; thus, this phase was near completion. Training students now became the focal point of the fire program, and this required a high level of instruction. With each year’s burn acreage escalating to near 30,000 acres, there was little room for wasted time or effort. Dr. Wright started a new class to facilitate this process, and it was simply called Prescribed Burning. One evening each week the class would meet for 3 hours, with Henry lecturing for an hour and the graduate student fire bosses conducting the rest of the class. The graduate students would review and critique the previous weeks field experiences with the class. This class raised to an all time high the level of instruction in the practical application of fire. The students that came out of this intense effort were excellent practitioners of prescribed burning.
Along with the increased training of students, another practical innovation was initiated. The first helitorch burn was conducted in 1982. The start of helitorch burning was not conceived within the program but came with a call from Renny Propst of Blackrock, Arkansas. I visited with Mr. Propst and he asked if we were interested in using a helitorch to ignite our juniper burns. I told him I felt we would be interested, but I would have to visit with Henry to finalize any agreement. When I approached Henry, he said absolutely no, that our fires were complicated enough without having to contend with a helicopter. Over the next few weeks, Henry relented and agreed to a demonstration ignition. Plans were made to have the helitorch come to west Texas and ignite a planned juniper burn near Guthrie, Texas.
The helicopter with helitorch arrived at the ranch headquarters right on time with Dr. Wright and all the fire crew anxiously waiting. The helicopter was towed on a trailer pulled by a pickup. As soon as the pickup stopped, two people got out and waved hello to us all. I was expecting to meet Renny Propst, but there was only a very large man and a very young teenager. I was very concerned as I was certain the helicopter could not carry the large fellow, much less the helitorch, and the teenager could only be someone’s son playing hooky from an Arkansas junior high. The two immediately began releasing the helicopter from its binding straps and then began attaching the main rotor blades to the machine. I was concerned; actually, I was becoming very frightened. I had talked Dr. Wright into this demonstration, and it was beginning to look as if I had made a terrible mistake in my dealings with the folks from Arkansas. My only salvation was that Mr. Propst would soon drive up to save the day. I began to offer fervent prayers for the arrival of Mr. Propst. This did not happen, and much to my dismay the teenager climbed into the cockpit and started the helicopter. My last glimmer of hope remained that he was only warming up the engine and Mr. Propst would soon come driving up the road to the ranch headquarters. All the while, Dr. Wright looked sternly at me with an expression that said, “Your next check from Texas Tech will be your last.” All hope was lost as the teenager pulled back the stick and, in a cloud of dust, flew the helicopter off the trailer. I was dead meat.
Jimmy Propst landed the helicopter, walked over and introduced himself to us all and, with a broad grin, asked Dr. Wright if he would show him the burn unit while we prepared the alumigel-gas mixture for the helitorch. As Henry climbed into the helicopter, I received another one of those looks. They returned in about 30 minutes, and we could not get Henry out of the helicopter for the next 10 years.
The helicopter ignition that day was less than spectacular. The helitorch was built to exude large blobs of jellied gas which gave a very spotty ignition in the sparse west Texas fuels. This resulted in a burn not superior to hand ignition with drip torches. Over the next few months, Henry, Guy, Al, and Bob discussed this problem among themselves and with Jimmy Propst. That summer they traveled to Blackrock, Arkansas and designed and built a system of small and large emitters which put out a continuous rain of small flaming droplets. This device proved to be a superior ignition system for west Texas juniper fuels.
Keith Blair was the next graduate student fire boss to make a contribution to the Texas Tech fire program. Keith had learned his skills from the previous graduate students and Henry. While burning blacklines during a wet spring, Henry and Keith were perplexed by the lack of juniper canopy ignition. Where the canopies were dense, it is desirable to have them ‘torch’ thus removing that fuel bridge which could carry the fire across the blackline when the unit was headfired. They started sampling the juniper foliage and determining fuel moisture content. After a couple of years, they determined that below about 70% foliage moisture the canopy was easily ignited. This became yet another of Henry’s thresholds and is an extremely important factor in ensuring a safe burn.
Juniper Burning
Burning juniper infested rangeland is nothing short of hard work. It requires a great deal of organization and preparation. Preparation should begin by writing a fire plan. This plan should include at least the objectives you hope to achieve, maps of the burn area, and prescriptions for the ignition of the blacklines and headfire. Writing this plan will help you think through every aspect of the prescribed burn.
The first step is to critically analyze the pasture in question. If the mature juniper canopy cover is not over 10%, there will be very little increase in forage production as a result of juniper control. However, if the pasture has numerous young juniper scattered throughout, then it is definitely the time to burn. Another situation that is critical occurs when a pasture has over 25% canopy cover of juniper. At this point the pasture is rapidly approaching a situation when the grass production is severely reduced. It is mandatory to have the grass fuel sufficient to carry a fire across a pasture. When the juniper canopy cover approaches 40%, the grass fuel is so reduced that a prescribed burn is generally not possible. To reclaim a pasture in this condition, some mechanical treatment is generally required to increase the grass fuel necessary to carry the fire.
One year prior to burning a pasture, the grazing management must be altered. The pasture must be allowed to accumulate as much grass as possible. Therefore, no grazing should be done at least during the fall growth period, and, if a good burn is to be made, the pasture should be rested during both the spring and fall growth period. Remember, the more fine fuel (grass) in the pasture, the greater the damage to the juniper and the easier the pasture will be to burn. With abundant fine fuel, the fire can be conducted under safer conditions with lower temperatures and higher humidities. With minimal fine fuel, such as found when a rancher removes the livestock the day before the burn, there is an unreasonable temptation to burn with higher winds, lower humidities, and higher temperatures.
Firelines should be marked during the fall prior to the winter burn. It is generally easiest to locate these firelines adjacent to the pasture fences. However, firelines should be moved away from fence lines to avoid extremely rough terrain or unusual jogs in a fence that make burning difficult. Assuming the prevailing wind in winter and early spring is from the southwest, black lines should be installed on the north and east edge of the pasture. Width of the blackline should be at least 500 feet. Thus, an additional mineral line should be placed 500 feet inside the perimeter mineral lines on the north and east pasture edges in preparation for burning in the blacklines. All the mineral lines should be checked for two features. First, the mineral lines should not have any grass or brush left in them. If any fuel is left in the lines, this provides an excellent fuel bridge to the outside of the burn unit. This will almost guarantee a fire escape. Second, the mineral lines should be reasonably smooth. The mineral lines provide vehicle access to the entire perimeter of the pasture and will be used repeatedly during all phases of the burn. Bull dozers will generally leave a very rough line. A little extra time to back drag the mineral line is generally worth a lot in the long run.
Blacklines should be burned out during January when temperatures are cool and humidities are frequently high. The 40 – 60 rule should be followed for this process. Remember, this is the most dangerous part of the prescribed burn as you only have the mineral line on the leeward side to protect against fire escape. Ignition should proceed at a slow and steady pace, with adequate numbers of spotters to look for and extinguish any accidental spot fires outside the burn area. Usually you should have at least six spotters plus a pumper truck with driver and pumper operator. At least half of the suppression crew should have radios to ensure rapid communication in case of trouble. The ignition crew should have at least four people. Three people should carry drip torches and one person keeping full drip torches available to all torch carriers. One experienced fire boss should direct all activities and coordinate the activities of the ignition and suppression crews. The one cardinal rule of ignition is always light moving into the wind. If you light moving with the wind the fire will overtake you and cause serious injury.
Two ignition techniques are especially useful when burning blacklines; the backfire and the strip headfire. With the backfire you can maintain a high level of control over the burning rate as the fire is backing into the wind. With this fire type, the flame lengths will be very short and the rate the fire spreads into the wind will be very slow. The only disadvantage to backfires is they can take a very long time to move across the 500 foot distance which must be burned out. This time period can be shortened by use of the strip headfire technique. This technique incorporates the advantages of a backfire with the increased speed of a headfire. The strip headfire ignition requires at least three torch carriers. The first torch begins ignition at the leeward edge of the blackline. This torch will light into the wind for at least 50 feet and allow the fire to back into the wind 10 to 15 feet. As the first torch carrier proceeds beyond 50 feet, the second torch starts lighting about 20 feet upwind of the backing fire from the first torch. The second torch is in essence starting two fires, one is a small headfire which burns out the strip downwind to the first torches backfire and the second is a simultaneous backfire which moves into the wind. As the first torch moves out to past 100 feet and the second torch approaches 50 feet from the starting point, the third torch starts ignition about 50 to 75 feet upwind of the backfire ignited by the second torch. This torch is also igniting both a headfire and a backfire. Therefore, there are three torches lighting simultaneously and each burning out strips of fuel and light head and backfires. The fireboss coordinates the spacing of the torches and the speed at which they move. This ensures that the second and third torches do not pass the first torch and run a head fire over the first torches position. With practice and experience, this process can become a thing of beauty to behold on a cool evening.
Burning blacklines will invariably run into the night. This is an excellent time to put in blacklines as the temperatures are becoming increasingly cooler and the humidity is rising. If you plan to burn, especially at night, you must visit with your regional office of the Texas Natural Resource Conservation Commission and inform them of your plans. This will save you a lot of grief and help ensure that prescribed burning remains a viable and legal rangeland management tool.
The final phase of a prescribed burn is the ignition of the main headfire which will burn the entire pasture. This is usually the safest part of the whole process. The south and west edges of the pasture are ignited. Again, the torches move into the wind and eventually meet at the southwest corner of the pasture. Obviously, this assumes that the prevailing wind is from the southwest. Spotters and fire suppression equipment are located on the north and east sides of the pasture to deal with any unlikely spot fires. Ignition should only take place when the air temperature is between 70 and 80F, relative humidity is between 25 and 40%, and the wind is between 8 and 15 mph. It is strictly ill-advised to start ignition if these conditions are expected to change, especially higher winds, higher temperatures, or lower humidities.
More detailed instructions are available in the form of three Management Notes published by the Department of Range, Wildlife, and Fisheries Management at Texas Tech University, Lubbock, TX 79409-2125. Our phone number is (806) 742-2841.
Summary
The key to successful burning of juniper infested rangeland in Texas is having adequate fine fuel. Ensuring the fine fuel load is adequate may be as simple as deferring the pasture from grazing in the fall growth period or possibly for one year. In other cases it may require a pretreatment to reduce the juniper density, thus allowing the grasses to respond and produce the fine fuel necessary for a successful burn. Therefore, a thorough plan must be initiated well before the actual burn is conducted.
Wildlife habitat must also be a critical focus in the planning process. How much juniper should be unburned in the pasture to ensure adequate hiding and thermal cover for deer and other wildlife species? It is suggested that areas of either steep slopes and/or shallow soils be excluded from the area that is burned. This will require extra firelines and care in ignition.
It is strongly suggested that pastures on the north and east edge of the planned burn be grazed closely in the months prior to the planned burn. By reducing the fine fuel (grass) in these areas, the potential for spot fires and fire escape will be greatly reduced. This will require a long-term grazing plan and in some cases a good working relationship with neighbors.
Finally, develop a good fire plan with realistic objectives and clearly stated procedures for the prescribed burn. This plan will be valuable in reminding you when different aspects of the process need to be accomplished. The plan also be a good checklist of equipment, personnel, and safety considerations necessary for a successful prescribed burn.
This paper is contribution No. T-9-772 from the College of Agricultural Sciences and Natural Resources, Texas Tech University.
Comments: Allan McGinty, Professor and Extension Wildlife Specialist