Most people involved in prescription burns within cemeteries when asked about possible damage to the gravestones will tell you that they have never observed any damage to the stones. One person from Iowa in response to the question responded "We have been burning cemeteries since 1988 here in Crawford County. I have not noticed any damage to the head stones in our program" and "you will have ashes laying on the top of the stones but once it rains they are gone. The fire moves so fast that the heat does not seem to build up on the stones". These statements define exactly the problems we are facing. While they may be able to determine the exact effects of the fire on the vegetation, most, in not all persons conducting prescribed burning within a cemetery are in no way qualified to determine what if any damage is being caused. Simple observation by the naked eye to an untrained observer cannot qualify as and must not be accepted as an informed opinion.

Possible problems resulting from the result of prescribed burning in a cemetery include:

• Heat from controlled burns may cause damage to adhesive joints fills with synthetic materials, lead wedges and mortar fills. Even while exposure of gravestones to heat is brief, heat causes chemical damages in these materials and they become unstable.
• By-products of the burnt vegetation (carbon deposits and flying ash) are deposited into the surfaces of the stones, adding a layer that will hasten deterioration.
• Rain, dew, and other forms of precipitation will drive particular matter from the burn into the stones pores and cracks, speeding up deterioration. Precipitation will also hasten deterioration of the restoration materials previously damaged by the heat.
• In cases where there may have been previous repair work, restoration dowels in broken monuments, particularly those that are situated close to the ground, are at risk of expanding under influence of heat, thereby possibly shattering fragile stones.

Dr. Ted Nield, Science & Communications Officer, Geological Society of London, studied Geology at University College Swansea, and University College Cardiff. After gaining his PhD he became a consultant carbonate sedimentologist. He confirms that burning vegetation would pose a significant danger to most, if not all gravestones.

"While the fire would blacken the stones and render them illegible and disfigure their natural stone colour, the heat would have very much more serious effects. Moisture in the pore spaces of many rocks used for gravestones would boil off and cause the stone to lose surface detail (which would be exploded off), further affecting legibility. Expansion and contraction caused by the heat could also easily cause surface layers to spall off, and can even crack stones completely. Oddly, the thicker and more sturdy looking the stone, the more likely this is to happen because the higher temperature gradients would set up massive forces through relative expansion and contraction across the greater thickness. Limestone gravestones would suffer from all of these effects, but would be worse affected still by the calcining effect of heat. An intense fire would disrupt the chemical bonds present in the complex carbonates that make up limestones, and would tend to turn the material into quicklime. This then dissolves in rainwater with the release of great heat, causing further degradation".

Battalion Chief Jim Smith of the California Department of Forestry and Fire Protection presented a paper at the 33^rd Annual Meeting of the Society for California Archaeology held in Sacramento in April 1999 entitled "Protecting Archaeological Sites With Prescribed Fire". While an advocate of prescribed burns he did make the statement "If the site contains significant features like rock art, special measures can be taken. Use of aluminum fire blankets to shield the art from the effects of smoke and heat may be needed".

According to the history of the Elsinore Valley Cemetery (18170 Collier Ave, Lake Elsinore, CA 92530) :"During the early years the cemetery ground was bare except for weeds. They grew so high that burning was used for their control. This caused damage to the trees and also the marble, wood, and limestone gravemarkers, so the burning was discontinued."

Government officials in County Kildare, Ireland seem to feel that burning in a cemetery is a problem as they address the issue in their cemetery maintenance policy. In the section on cleaning they state "Burning or chemical killing of weeds should not be undertaken as these tend to encourage a rigorous secondary growth of nettles and weeds and may also cause damage to headstones". They continue  in the section on Trees and Shrubbery  "None of the debris gathered in this way should be burned within the graveyard boundary, as this will cause damage to grave markers and/or stonework".

While as a rule these fires are closely monitored, they have been know to got out of control.  On December 10, 2002 the Scotland County Fire Department responded to a grassfire north of Memphis. A controlled burn near the Mt. Olive Cemetery, which is located just south of the Iowa line, had gotten out of control and spread into some adjoining brush as well as a shelled corn field. The department was able to quickly bring the fire under control and was on the scene for approximately 30 minutes extinguishing hot spots in the brush. The fire destroyed an estimated three acres of grass. Eight firemen responded to the call taking four fire trucks to the scene.

Prescribed Fires

In general there are two distinct types of cemetery burning. The first, where vegetation is first cleared and then placed in piles away from the gravestones to be burned, is not at issue here, although it goes without saying that if the cemetery contains wooden grave markers, or markers whose composition is unknown, there should be no attempt at burning anywhere in the vicinity. There have been many documented cases where a caretaker accidentally destroyed all or most of the old wooden markers when he was burning off dead grass or other overgrowth. Wooden markers that have been whitewashed, or have blackened with age, may be mistaken for stone or bronze, their true nature remaining undiscovered until after they have been damaged. The composition of all markers should be conclusively determined before beginning any sort of restoration work or cleanup.

This article will focus on the second type of controlled burning. The sole purpose of controlled burning within a cemetery is for maintaining native vegetation and wildflowers. Usually these controlled fires are being used to maintain neighboring areas, but spread into cemeteries, known or unsuspected, that lie along their paths. The effect of such repeated controlled burns on markers, monuments, and other identifying features of a cemetery has not been considered, and the possibility of cumulative damage needs to be seriously addressed.

The State of California has defined prescribed burning as follows; "A prescribed burn is an intentionally set fire, in a wild land setting.  Prescribed burns, also known as controlled burns, are widely used to manage ecosystems, since they aid in: restoration and maintenance of biological diversity, forest regeneration, forage production for wildlife, timber stand improvement, and wildfire hazard reduction". According to the Northern Prairie Wildlife Research Center, there are three basic kinds of prescribed fires:

• Backing fires. Backing fires burn into the wind. Fire is started along a prepared base line, such as a road, plowed line, stream, wetland, or other barrier, and allowed to burn into the wind.  Backing fires are generally the easiest way to burn. Flame lengths are shorter, rate of fire spread is slow, and smoke density is generally less than in head or flank fires. Backing fires burn hotter at the ground surface and do a better job of total fuel consumption than head or flank fires.
• Head fires. Head fires burn with the wind. They have greater flame lengths, faster rates of spread, greater smoke volumes, and burn cooler at the ground surface than backing fires or flank fires. Because head fires burn faster than other kinds of fires, containment becomes more critical as wind speed and fuel quantity increase.
• Flank fires. Flank fires burn at oblique angles to the wind direction. They are a modification of backing fires in that lines of fires are set to burn into the wind but at angles to the wind direction. Flank fires are often used to secure the flanks of a head fire as the head fire progresses. This method of firing can stand little variation in wind direction and needs expert crew coordination and timing.

Some experts tell us that a single burn may actually increase the problem of woody plant invasion. Using fire once is not very helpful. It must be used repeatedly in a planned strategy to be effective.

Prescribed Fire Movement Speeds

A well-controlled head-fire , in recommended weather conditions, will move forward at a rate of about 1.7 - 16.5 feet per minute. In relatively moist conditions and low wind speeds the rate of spread will be at the lower end of this range while in dry conditions and relatively strong winds rates of spread towards the upper end of the range will be encountered. Rates of spread of 3  - 5 feet per minute are about average. Rates if spread of up to 26 feet per minute may be encountered with head-fires in heavier, drier fuels or relatively high wind speeds. Rates of spread can be much greater when the weather and fuel conditions are outside the recommended limits, and wildfires can move at speeds of 30 feet per minute or more. Back-fires spread much more slowly, normally at between 1.7 - 2.5 feet per minute. Smoldering grassland fires move very much more slowly.

Effects Of Prescribed Fire Temperature On Gravestones

When the temperature of a potential fuel is raised by heating, its chemical constituents are broken down into more volatile and flammable substances. In the presence of oxygen these undergo further vigorous chemical reactions, accompanied by the production of heat and, usually, the presence of visible flames. Once a critical temperature is passed more heat is generated than is absorbed and self-sustaining combustion begins. This is the point of ignition. For most plant fuels the critical temperature for ignition is just above 300.ºC. The hot gases produced during combustion cool rapidly outside the flames, the cooling effect increasing with increasing speed of the wind. Flame size and fire intensity are closely related, with fire intensity increasing in proportion to the square of the flame length - a doubling in flame length indicates a fourfold increase in the rate of heat production by the fire. As well as volatile compounds, charcoal (or char) is also produced. This is largely composed of carbon. The decomposition of the fuel to char or to volatile gases can be competing processes. Char is produced at lower temperatures than volatiles and its production is enhanced if the fuel has a high mineral, or ash, content. This is the basis of action of many chemical fire retardants. It is possible for char to burn by 'glowing' combustion or smoldering. This occurs at the surface of the solid fuel and is less intense than flaming combustion. It requires less oxygen (only about a third as much) and so can occur in more densely packed fuels. In woodland management fires, the fuel that is not completely burnt by the flames generally cools so rapidly that glowing combustion is sustained for no more than a few minutes. However, a smoldering grass surface is less exposed to heat loss and glowing combustion may continue for extended periods.

The variety of stone materials are already weathering at different rates as a result of normal climate changes.  It follows then that artificially induced severe temperatures and the accelerated rate of temperature change coupled with any chemical residues of burned material may hasten deterioration.  According to Shelley Sass, an Architectural Conservator
for the Sass Conservation of Yonkers, NY, there is documented evidence of stone damage from fires where the heat was 1600 degrees F that confirm high temperatures are extremely and immediately damaging to most stones. It would not be outside of the bounds of reason to suspect that controlled burns have a lower temperature ( some research indicates recorded grassland fire temperatures as high as  600 to 700 degrees F range), depending on the nature of the plant material. In the case of grassland fires research has proven that the hottest temperatures were recorded at about 15 cm above ground in a headfire and at about 5 cm above the ground in a backfire.  Temperatures also may be influenced by the use of any accelerant, the quality of the accelerant, the quantity used and how is it used.  However, longer exposure to lower levels of heat can damage both stones and repair materials, at least on a microscopic level, due to the stress exerted by differential thermal expansion, as two unlike materials react to temperature changes differently. This type of damage often is not immediately evident, but will become visible only after the first (or several) freeze/thaw seasons. If it is possible to ascertain the average temperature range and duration for a burn, it should be easy to predict the type of damage the gravestones in these cemeteries would sustain.

According to The Scottish Executive, two of the most important factors affecting ease of ignition are moisture content of the fuel and its starting temperature. Burning in the winter half of the year, when conditions are cool and not too dry, greatly reduces the risk of very intense and uncontrollable fires. If the potential fuel is cold it will take more heat to raise it to the critical temperature.

Even more important than temperature is the moisture content of the potential fuel. This is because water requires unusually large amounts of heat to raise its temperature, and to change from liquid to vapour. If there is a lot of water present it will be difficult to reach the critical temperature for sustained combustion. Until the water is entirely evaporated, at least from the surface layers of fuel, the temperature will not rise above 100 ºC and a fire will not ignite.

Fresh green foliage of deciduous plants often has such a high moisture content (up to 300% or more of dry weight) that it is very difficult to ignite. Evergreens, like heather or conifers, often have somewhat lower moisture contents, and a higher content of volatile resins, waxes, oils and similar compounds, and will burn more readily. The amount of heather present in moorland vegetation is often a principal determinant of the temperature and intensity of a fire. Normally, there is considerable variation in moisture content within the vegetation. The layer of plant litter, mosses and lichens under the heather may have a moisture content of 200 - 300 % while loose plant litter supported among the shoots of the heather canopy may have a moisture content of only 25%. The moisture content of the heather canopy is likely to be in the range 50% - 100% during the muirburn season. On dry, well-drained ground, moisture contents of the vegetation and litter may become less than 50%.

Dead plant material dries out more quickly and fully than living material, burns even more readily, and often initially carries the fire. The moisture content of dead grass leaves can change from 90% to 20% in less than half an hour under drying conditions. The dead leaf litter from purple moor-grass is one of the first fuels on moorlands to dry out, other than when it forms a compact, damp mat in close contact with the ground. Decomposition of plant litter is often slow on moorlands, significant amounts of dead plant material can accumulate, and this can greatly affect the intensity and rate of spread of fires.

The amount of heat required to dry the fuel is generally a small proportion of the heat released once a fire is self-sustaining. Therefore, much more water is needed to put out a fire, once started, than is required to prevent a fire starting in the first place.

Indiana - The DNR and The Nature Conservancy

Bundy Cemetery, Stony Creek Township, Henry County, Indiana

Currently the Indiana DNR in Cooperative Agreement with The Nature Conservancy conducts controlled burns over remnant prairie plants on properties for which they are responsible. Some of these properties contain historic pioneer cemeteries. During 2002 prescribed fire was carried out on 625 acres at 16 sites by the Indiana DNR - Division of Nature Preserves along with assistance from other DNR divisions, private conservation groups and volunteers. An additional 4 burns totaling 38 acres were conducted by private contractors.  According to John Bacone, Division Director, DNR - Division of Nature Preserves the following cemeteries are DNR managed  :

In addition one or two land trusts have agreements with several of the trustees to manage a few other pioneer prairie cemeteries in an effort to keep the original vegetation from disappearing from the entire county.


The members of the Indiana Pioneer Cemeteries Restoration Project (INPCRP) are concerned about the potential damage these burns may cause to tombstones. They note that the stones turn a smoky gray color after the burn and are concerned about the effects the burns might have on epoxies, lead wedges, and mortars. The official DNR opinion is that the burn is quick and does not harm the tombstones. However visually looking at the stones over a period of time is not a study, (Arlindo Begonha in his 1997 PhD thesis presented at University of Minho, states that some scientific studies of the decay in granitic monuments included the use of optical microscopy, X-ray diffraction, scanning electron microscopy, infrared spectrophotometry, ionic chromatography, and plasma and atomic absorption spectrometry tests were used in order to characterize mineralogically and chemically the fresh and weathered rock as well as the stone pathologies in the monuments) unless the degree of knowledge of the preexisting condition of particular stones is within the scope of the knowledge of the person/persons conducting the burn, or affiliated with them, and they can certify no damage has occurred.

To the outside observer, it would appear that that the parent agency, DNR, with its keen interest in the survival of native vegetation, is perhaps trumping the real concern by many for the welfare of the pioneer cemeteries that are being subjected to burning. Without question the folks who work within the DHPA are concerned with all of Indiana's cultural heritage which would of course include Indiana's pioneers and their cemeteries. It may not, however, be within their power to simply overrule decisions from above even if they were to concur that cemetery burnings are adverse. The end result may be that there are at least two elements within the same bureaucracy that have differing opinions when the preservation of cultural and natural resources are at odds as they seem to be in this case.

In the spring of 2003 Henry County, Indiana legislators met with the Henry County Cemetery Commission to better understand some of the problems and issues with Indiana Pioneer Cemeteries. The Henry County Cemetery Commission was assured that these issues would be explored further in 2003 Interim Study Committees at the Indiana statehouse. In June,  2003 cemetery law issues were assigned to County Government Study Commission. The first public
hearing was held on July 31st before the study committee, and a number of concerned persons from throughout the state presented information on problems involving current legislation on pioneer cemeteries. Among the  items addressed were cemeteries located in “Prairie Grass Restoration” areas and controlled burning in cemeteries. The next Study Committee Hearing is scheduled for Sept. 3rd, 2003 at 10:30 am in room 431 at the Indiana Statehouse.
 

Prescribed Burning Data Recording

On the subject of prescribed burning there is a wealth of recorded data covering not only the fires themselves but the effects generated as a result of fire. The United States Department of Agriculture (USDA) Forest Service maintains the Fire Effects Information System database containing extensive data concerning the effects of fire on Vegetation and Wildlife.

Groups such as The Nature Conservancy that are involved in prescribed burning have clear rules and regulations defined in a fire management manual that must be followed. In order to conduct a prescribed burn there is specific data that must be included in a written prescribed-burning plan that must be recorded for every burn.  At the beginning of the prescribed burn, record wind speed and direction, fuel moisture, humidity, burning index, temperature, days since and amount of last rain, and dampness of soil and lower litter. Also record fire behavior data such as type of fire used, length of flames, and forward rate of spread. Continue to record applicable weather and fire-behavior parameters at 2- to 3-hour intervals throughout the burn. After the burn, record amount of crown scorch, consumption of brush, litter; and duff, and any other evidence of fire intensity such as unburned areas, exposed mineral soil, and cracks in bark or cupping on the lower bole due to bark consumption. Also should be included is a short narrative on success of the burn. Some instructions instruct the person preparing the plan to "Give instructions for the protection of sensitive areas" and to "consider historical and archeological sites". However they do not offer any specific guidelines to be followed in this consideration.  Saving Graves feels that the same data reporting as it relates to cemeteries within a prescribed burn area should be required. With that in mind, we support the development of the following plan.

Building A Database

The first step that needs to be taken is the development of a database or a master index of cemeteries that are previously or currently a part of a prescribed burn program. Currently there only a very few known cemeteries that are part of a burn program; however there are strong indications that the actual numbers may be quite high. Before we can gather a clear understanding of the problem we must be able to determine how widespread it is. The database should contain the following information broken down, first by state, then by county:

• A listing of all known prescribed burn cemeteries.
• The dates of all previous burns and scheduled future burns.
• A copy of the Monitoring Report for each burn.
• A photographic record (before, during and after) of each and every burn within a specific cemetery.
• A listing of all trained monitors for that specific area.

Training Monitors

There must be trained observers present before, during, and after each burn to examine the stones microscopically and submit their own independent reports. The purpose of training is to provide resource specialists with the necessary skills for implementing projects and collecting reliable, unbiased, and consistent data. Examiners should understand data collection, documentation, analysis, interpretation, and evaluation procedures, including the need for uniformity, accuracy, and reliable monitoring data.

The Monitoring Plan

If we are to understand the possible effects of a prescribed burn on a cemetery there must be a monitoring plan that explains the rationale for the monitoring project, documents the goals and objectives, and describes the monitoring methodology in enough detail to direct continued implementation. Monitoring plans serve five important functions:

• A plan provides a full description of the problem, the objectives, and the proposed methodology.
• Draft monitoring plans provide a means to solicit input from many participants.
• A final monitoring plan consolidates all information into a single document that can be easily accessed and referenced.
• A final monitoring plan documents the location and techniques of the monitoring in sufficient detail that a successor can continue the monitoring.
• A final monitoring plan documents the commitment to implementing a monitoring project and the management that will occur based on monitoring results. A monitoring plan can also be signed by all participants to demonstrate their support for the project and acceptance of the proposed management changes that may result.

In order for us to obtain a full understanding of the possible effects on the prescribed burn on the gravestones the monitoring reports should include at a minimum the following:

General Conditions

• Air temperature at the time of the burn. Are the stones cold when the quick heat from the fire hits them)
• Temperature at varying places in the cemetery at varying heights (ground level, middle, and extreme heat at the
  crest of the fire near the top of the stones) and density (the grass, weeds, and wildflowers are thicker in places, causing hotter temperatures as they burn) during the burning.
• Average height of the grass, weeds, or wildflowers.
• Atmospheric humidity at the time of burning.
• General weather conditions for a period of time leading up to the burn. Since these stones are porous there is more risk of damage if they're moist from rain than if it's been dry for a while.
• Before, during and after burn photographs.
• The date and time of day of the burn.

Gravestone Conditions

• Moisture content in the stones at the time of the burn.
• Type of material the stones are composed of.
• Age of the stones (if can be determined by dates).
• General condition of the stones, including examination of each stone for weak, cracked, or flaking areas.
• The temperature of the surface of the stone before, during and after the burn.
• Vegetative growth on or in the stone itself, such as moss, lichens, or seedlings, that may cause the fire to focus more intently on certain points on the stone itself as they burn away.

Evaluation post fire:

• Effects should be measured at various reference points after the fire. Permanent photo-points might help with this.

Collecting this information should give us an indication of the effects to a gravestone caused by controlled burning. Is it enough to cause a failure? As of now, no one really knows for sure. One thing that we do know is that The Nature Conservancy or the DNR are not qualified in the field of gravestone repair or restoration. They cannot make an educated judgment as to the effects of a controlled burn on gravestones and we should not rely on them to tell us that it is ok. Currently our lack of information on which to base our decisions and actions is deplorable.

Scientific monitoring requires an investment of time and money with returns from this investment sometime in the future usually accruing to people not making the original investment.  It is not simple.  It does not always accomplish what is needed, because of cost, procedure or system design flaws.  In many cases it is often difficult to determine or agree upon what to monitor. The monitoring and evaluation process is not easy, but if we are to attempt to discover a definitive answer to the question of the effect of controlled burning within a cemetery it must be an integral part of the process. The only way to understand what we are doing is through systematic scientific monitoring on a regular basis. 

Alternatives to Burning

While prescribed burning within a cemetery is clearly an area of many unanswered questions, it does seem logical that the fields of cemetery preservation and nature conservation can and should work closely together in achieving their respective goals. In January of 1997, the California Native Plant Society started a project that would transform the Old City Cemetery in Sacramento into the California Native Plant Demonstration Garden.  The goal of the project is to enlighten visitors to the beauty of California native plants, illustrate how they can be used in the home garden, show how to attract wildlife and beneficial insects, and educate about the many medicinal, cultural and edible aspects used by the local Native Americans. At the same time, the group played a major role in the restoration and preservation of a valuable historic community resource, the formerly neglected Old City Cemetery. Information on the ongoing project can be found at http://www.sacvalleycnps.org/projects/demoGarden.html#garden.  You must keep in mind that one of the reasons that this project works is that it is set in a urban environment. It is quite likely that a similar project in a rural environment  may not archive the same degree of success. 

There are also examples of cemetery and nature preservation groups working hand-in-hand to achieve their goals. In the United Kingdom The Garden History Society, who list among their objectives to promote the protection and conservation of historic parks, gardens and designed landscapes, and to advise on their restoration, works closely with the Commonwealth War Graves Commission. The Commission was established by Royal Charter in 1917. Its duties are to mark and maintain the graves of the members of the forces of the Commonwealth who were killed in the two World Wars, to build memorials to those who have no known grave and to keep records and registers, including, after the Second World War, a record of the Civilian War Dead.

A Final Thought

A cemetery must be the object of special care in order to safeguard its integrity and ensure that it is cleaned and presented in a seemly manner. The work of cemetery conservation and restoration is a highly specialized operation and should be inspired by the the highest principles. Its aim is to preserve and reveal the aesthetic value of the specific gravestone and overall historic value of the cemetery. When there is any doubt as to the potential effect of any method, one must err on the side of caution. If the benefits of an action are unknown, clearly at the same time one can't be certain one is not causing harm. One person who was interviewed for this article told us that he burned many prairie cemetery and never once saw a tombstone damaged. When further questioned he admitted that he had no supporting data for his statement and that "Much research has been done on grass fire temperature but none that I know relating to tombstones". The Venice Charter, the international charter for the conservation and restoration of monuments and sites states in Article 2. "The conservation and restoration of monuments must have recourse to all the sciences and techniques which can contribute to the study and safeguarding of the architectural heritage".

Applying the best available science to the potential threat of prescribed fire while at the same time supporting the best practices for preservation and restoration at cemeteries is vital. While we have some good indications, the lack of scientific information on the effect of fire to historic gravestones is a critical barrier to taking appropriate action. Currently is impossible to determine the potential damage caused to a cemetery by a prescribed burning program. Saving Graves is prepared to take the initiative and lead the way in working with partners around the world to identify, prioritize and address gaps in this knowledge so that we can have a clear understanding and resolution to this question.