INTRODUCTION TO

PRESCRIBED FIRE IN 

SOUTHERN ECOSYSTEMS

United States

Department of

Agriculture

Forest Service

Southern Research 

Station

AUGUST 2012

Science Update 

SRS-054
PRESCRIBED BURNING IS

FIRE...

• Applied in a skillful manner

• Under exacting weather conditions

• In a definite place

• To achieve specific results

The objective of 

this Introduction 

to Prescribed 

Burning

To help resource managers 

plan and execute prescribed 

burns in Southern forests and 

grasslands by:

• Explaining the reasons for 

prescribed burning

• Emphasizing the 

environmental effects

• Explaining the importance 

of weather in prescribed 

burning

• Describing the various 

techniques of prescribed 

burning

• Giving general information pertaining to prescribed 

burning

www.srs.fs.usda.gov

August 2012

Southern Research Station

200 W.T. Weaver Blvd. 

Asheville, NC 28804

ERRATA:

An error occurred during the preparation of a content table within SU-SRS-054, 

Introduction to Prescribed Fire in Southern Ecosystems.

To correct this error, the content table on page 30 of this publication was replaced on July 1, 2013. 
INTRODUCTION TO 

PRESCRIBED FIRE IN 

SOUTHERN ECOSYSTEMS

Revised in 2012 by Thomas A. Waldrop and Scott L. Goodrick, 

Southern Research Station with portions contributed by Craig A. 

Harper, University of Tennessee, and Gene Towne, Konza Prairie 

Biological Station, Kansas State University.

This guide was originally written in 1966 by Merlin J. Dixon, 

Southern Region, USDA Forest Service. Revisions were completed 

in 1973 and 1979 by lead author Hugh E. Mobley, Southern 

Region, USDA Forest Service. The guide was rewritten in 1988 by 

Dale D. Wade and James D. Lunsford, Fire Management, Southern 

Region, USDA Forest Service.

Substantial information found in this guide came from the 

Rainbow Series of Wildland Fire in Ecosystems, sponsored by the 

Interagency Joint Fire Science Program. These publications are 

listed under Suggested Reading at the end of the guide. 

Photographs were provided by the Auburn University Archive, 

Auburn University; David Guynn and Aaron Stottlemyer of 

Clemson University; Ron Halstead, Halstead Forestry & Realty, 

Inc.; Dale Wade of Rx Fire Doctor; Mike Bozzo of the SC Forestry 

Commission, and numerous employees of the USDA Forest 

Service.

Appreciation is expressed to various State and Federal Agencies, 

private industries, and other organizations for their helpful reviews, 

suggestions, and comments.

Sponsored for publication by Fire Management, Southern Region, 

USDA Forest Service in cooperation with U.S. Forest Service 

Southern Research Station.

This guide provides basic information needed to help you become technically proficient in the proper planning and use of prescribed 

fire. A glossary toward the end of this manual will help with unfamiliar terms. To learn more about the subject of prescribed fire, a 

list of suggested readings follows the glossary. Nearby State and Federal resource management agencies are also excellent sources of 

information. Many of the agencies provide periodic training in fire behavior and prescribed fire.
i

Contents PAGE

IntroductIon ................................................................................................................................................ 1

 History and Ecology of Fire ...................................................................................................................... 1

 Present Use ............................................................................................................................................... 2

 Impact of Prescribed Burning ...................................................................................................................... 3

reasons for PrescrIbed fIre In forest and Grassland ManaGeMent ...................................... 5

 Reduce Hazardous Fuels ...................................................................................................................... 5

 Dispose of Logging Debris ...................................................................................................................... 6

 Prepare Sites for Seeding or Planting ......................................................................................................... 6

 Improve Wildlife Habitat ...................................................................................................................... 6

 Manage Competing Vegetation ................................................................................................................. 7

 Control Insects and Disease ................................................................................................................... 8

 Improve Forage for Grazing ................................................................................................................. 8

 Enhance Appearance and Access ......................................................................................................... 9

 Perpetuate Species and Communities that Require Fire ........................................................................... 9

envIronMental effects ............................................................................................................................ 11

 Vegetation .............................................................................................................................................. 11

 Soil .......................................................................................................................................................... 12

 Water Quality ............................................................................................................................................. 13

 Air .......................................................................................................................................................... 13

 Human Health and Welfare .................................................................................................................... 14

 Wildlife .............................................................................................................................................. 15

 Aesthetics ..............................................................................................................................................17

Weather and fuel consIderatIons ....................................................................................................... 19

 Introduction ............................................................................................................................................. 19

 Important Weather Elements ................................................................................................................... 19

 Collecting and Using Weather Information on the Burn ............................................................................ 33

 

fIrInG technIques ........................................................................................................................................ 35

 General .................................................................................................................................................... 35

 Backing Fire ........................................................................................................................................... 35

 Strip-Heading Fire ................................................................................................................................. 36

 Flanking Fire .......................................................................................................................................... 37

 Point Source Fires ................................................................................................................................ 38

 Prescribed Burning on Slopes .................................................................................................................. 39

 Aerial Ignition ....................................................................................................................................... 40

 Center and Circular (Ring) Firing ....................................................................................................... 41

 Pile and Windrow Burning ................................................................................................................. 41
ii

PAGE

sMoke ManaGeMent ................................................................................................................................ 43

 Introduction ............................................................................................................................................ 43

 Smoke Management Planning .................................................................................................................. 43

 Daytime Smoke Evaluation ................................................................................................................... 44

 Nighttime Smoke Evaluation ................................................................................................................. 50

 Other Points to Consider .................................................................................................................... 52

 Executing a Smoke Management Plan .................................................................................................... 53

PlannInG the PrescrIbed burn ................................................................................................................. 55

 The Written Plan ................................................................................................................................. 55

 Simple Understory Prescribed Burning Unit Plan ............................................................................. 58

 Understory Prescribed Burning Unit Plan ......................................................................................... 59

 Postharvest Prescribed Burning Unit Plan .......................................................................................... 60

PreParInG for the PrescrIbed burn ...................................................................................................... 61

 Establishing Control Lines ................................................................................................................... 61

 After Control Lines are Established ...................................................................................................... 61

 Burn Unit Map ........................................................................................................................................... 61

executInG the burn ................................................................................................................................. 63 

 Checklist ............................................................................................................................................. 64

 

evaluatInG the burn ................................................................................................................................ 65

 General Points to be Considered ................................................................................................................ 65

 Points in First Evaluation ................................................................................................................... 65

 Points for Second Evaluation .................................................................................................................. 65

 Indications and Guidelines ................................................................................................................... 65

coordInatIon of burnInG .................................................................................................................... 67

General rules ............................................................................................................................................. 69

red flaG sItuatIons ................................................................................................................................ 70

Glossary ......................................................................................................................................................... 71

suGGested readInG ................................................................................................................................. 76
This publication is not intended to be a substitute for experience and training. Predicting fire behavior and smoke movement is difficult. The 

consequences of a mistake can be dangerous and costly.
Introduction

Prescribed burning can be used in many ecosystems throughout the southeastern United States to create or maintain desired conditions.

HISTORY AND ECOlOGY OF FIRE

The history of fire in the forests and grasslands of the South 

is as varied as the different ecosystems that span this large 

region. At times, fires burned as often as once a year or more 

in Coastal Plain pine systems or as infrequently as every 50 

years or more on north-facing or cove sites in the mountains. 

Lightning served as a major fire source in most ecosystems 

for millennia before Native Americans arrived some 10,000 

to 12,000 years ago. At that time, most plants had developed 

adaptations to either survive a fire or to regenerate after one. 

Native Americans were the first people of North America to 

use what we now call “prescribed burning.” Many preferred 

open grassland or savannah resulting from frequent 

burning— environments that provided access to grazers 

and browsers and to the wild grains, berries, and legumes 

that appeared after fire. European settlers, whose livelihood 

often depended on hunting and herding, quickly learned 

the advantages of firing the southern woods to control thick 

understory growth and provide abundant forage and browse. 

By the late 19th century, the logging industry had become 

established throughout the South. Excessive logging, 

followed by wildfires fueled by logging debris, left millions 

of acres of forest land with no trees. The need to control fire 

was evident to allow forests to regenerate; even prescribed 

fire was banned on lands managed by some agencies. 

Although fire was never completely removed from the 

landscape, its use was diminished for several decades until 

early reports suggested the advantages of prescribed fire 

for bobwhite quail habitat and for managing longleaf pine. 

By the 1950s and 1960s, active programs were established 

for prescribed burning in Coastal Plain and lower Piedmont 

pine and grassland habitats. 

Prescribed burning in the mountains did not begin until 

the 1980s but this practice is gaining acceptance for some 

management objectives.

Forests and grasslands of the South are well adapted 

to fire with species that have survival or regeneration 

strategies that not only tolerate fire but also may require it. 

Adaptations such as thick bark, light or winged seeds, or 

buried buds or meristems are common. Communities that 

have been burned frequently, such as Coastal Plain longleaf 

pine, often have few trees in the overstory with a highly 

diverse understory of fire-adapted plants. Communities 
2

Use of prescribed burning, as a component of an overall 

strategy of forest management, can help to maintain healthy 

forests. Credit for top photograph: Auburn University Archive, 

Auburn University, Bugwood.org

burned infrequently, such as Piedmont or Appalachian 

hardwoods, may have a diverse collection of overstory trees 

which can regenerate after an intense fire by basal sprouting. 

Although much experience is needed, fire can be used to 

meet landowner objectives if the fire prescription matches 

the life requirements and adaptations of the plants within 

the community.

PRESENT USE

Prescribed burning is an important tool throughout Southern 

forests, grasslands, and croplands. In 2011, over 6.4 million 

acres were burned by prescription for forestry purposes in 

the 13 Southern States. Prescribed burning is a desirable and 

economically sound practice in many forests and grasslands; 

in many cases, it is the only practical choice. Few, if any, 

other treatments have been developed that can compete 

with prescribed fire for its combination of economy and 

effectiveness. Chemical and mechanical treatments can 

be 10 to 20 times more expensive than prescribed burning 

and can have environmental costs such as destruction 

of habitat and soil erosion. Prescribed burning can also 

have environmental costs associated with smoke and soil 

exposure but these problems can be reduced with a good fire 

prescription and careful execution of the burn. 

In this guide, prescribed burning is described as fire 

applied in a knowledgeable manner to forest and grassland 

fuels on a specific land area under selected weather 

conditions to accomplish predetermined, well-defined 

management objectives.

This manual is intended to help resource managers plan 

and execute prescribed burns in Southern forests and 

grasslands. Until the 1980s and 1990s, prescribed burning 

was most common in Coastal Plain and lower Piedmont 

forests. Several generations of resource managers gained 

experience and knowledge with prescribed burning in those 

regions and much of our current knowledge originated 

there. More recently, management objectives have become 

broader, particularly on government lands. Managers and 

researchers have a new appreciation for using prescribed fire 

in grasslands, in hardwood forests, and on steep mountain 

slopes. Burning in these areas presents new challenges and 

complexities. This manual will serve as an introduction to 

prescribed burning in each of these regions and fuel types 

but should not be used as a substitute for experience. 

Grid ignition.

Pre-burn planning and safety meeting.
3

Smoke obscuring a highway. 

IMPACT OF PRESCRIBED BURNING

Most forests and grasslands require multiple prescribed 

fires over a number of years to fully reach management 

objectives, but even a single fire can provide multiple 

benefits. One prescribed fire can reduce wildfire hazard by 

reducing fuels, improve habitat for some wildlife species, 

reduce competition, enhance appearance, and 

improve access. 

Prescribed fires are not always beneficial. When conditions 

are wrong, fire can severely damage the resources they are 

intended to benefit. In forests, fire can reduce health or kill 

trees, understory plants, and animals. Prescribed fires can 

temporarily reduce air quality, although usually to a lesser 

degree than wildfires, particularly in communities and urban 

areas located near large wildland tracts. A prescribed fire 

that escapes its planned boundaries immediately becomes 

a wildfire. Proper planning and resources are required to 

prevent this danger and to control it if it should occur. 

Each prescribed fire presents a number of tradeoffs that 

must be recognized and carefully weighed to reach a 

decision regarding if and when to burn. Proper planning 

and execution are necessary to minimize any detrimental 

effects. Potential off-site impacts such as air quality and 

downstream water quality should be carefully considered, 

as should on-site impacts to soil and aesthetics. Opinions 

of the general public should always be respected as most 

are highly concerned about local and global environmental 

quality. Resource managers should work with their 

neighbors through open communication and consider their 

concerns when defining burn objectives. 

Prescribed fire is a complex tool and should only be used 

by those trained in its use. Proper diagnosis and detailed 

planning are needed for every area where burning is 

contemplated. The incomplete assessment of any factor 

can pose serious liability questions should fire escape or its 

smoke cause damage. A prescribed fire that does not achieve 

its intended objective(s) is a loss of both time and money, 

and it may be necessary to reburn as soon as sufficient fuel 

accumulates. Keep in mind that some resource management 

objectives can be met with a single fire, some require several 

fires in fairly quick succession, and some can only be 

accomplished by burning periodically over several decades.

5

REDUCE HAzARDOUS FUElS—Without fire, 

forest fuels can accumulate rapidly. Heavy “roughs” can 

accumulate quickly in pine stands, posing a serious threat 

from wildfire to all forest resources. Fuels on the forest floor 

in hardwood stands may accumulate more slowly than in 

pine stands. However, after a prescribed burn, these fuels 

can build up to or even exceed the dangerous pre-burn levels 

within three to four years. 

Prescribed fire is the most practical way to reduce dangerous 

accumulations of combustible fuels in Southern forests and 

grasslands. Wildfires that burn into areas where fuels have 

been reduced by prescribed burning cause less damage and 

are much easier to control. The appropriate interval between 

prescribed burns for fuel reduction varies with several 

factors, including the rate of fuel accumulation, past wildfire 

occurrence, values at risk, and the risk of a wildfire. The 

time interval between fires can be as often as every year 

although a 3- or 4-year cycle is usually adequate in forests 

after the initial fuel-reduction burn. Shorter cycles are 

necessary in grasslands to prevent shrub encroachment.

The need to reduce hazardous fuel accumulations is 

increasing throughout the South. Without fuel reduction, 

fire hazard can be extremely high in vast contiguous 

stands. Also, the rapidly-growing population of the South 

is expanding its wildland-urban interface and greatly 

increasing the number and value of resources that must be 

protected. The initial hazard-reduction burn in young forest 

stands requires exacting conditions of wind, humidity, 

and temperature.

• Reduce hazardous fuels 

• Dispose of logging debris

• Prepare sites for seeding or planting

• Improve wildlife habitat

• Manage competing vegetation

• Control insects and disease 

• Improve forage for grazing 

• Enhance appearance and access

• Perpetuate species and communities that 

require fire

Higher wind velocities and cooler temperatures minimize 

scorch damage in pine forests. Southern pine plantations 

averaging 10 to 12 feet in height can be burned by 

experienced people under the right conditions without 

damage. Aerial ignition can be used in young plantations for 

the first time when they are 15 to 20 feet tall by using close 

spacing of ignition spots, e.g., 100 by 100 feet, and cool, 

damp conditions with some wind to avoid crown damage. 

Hardwoods are susceptible to stem damage from even 

cool prescribed fires until they reach 6 to 8 inches in dbh 

(diameter at breast height— 4.5 feet above ground). After 

that, burning must be conducted under relatively cool, damp 

conditions if tree damage is a concern. 

Subsequent fuel reduction burns in pine and hardwood 

forests need not cover the entire area. The objective is to 

break up fuel continuity. Fuel reduction on 75 to 80 percent 

of the area is sufficient. An added advantage of “patchy” 

burns is that the unburned islands provide cover for 

wildlife. These unburned patches will not have a dangerous 

accumulation of fuels at the time of the next burn if they 

resulted from a lack of fuel during the previous fire. If, 

however, they were too wet to burn, these islands could 

result in hot spots the next time if a heading fire is allowed 

to sweep through them under appreciably drier conditions. 

Excessive crown scorch or stem damage could result in 

additional fuel accumulation through needle drop or even 

tree mortality.

Reasons for Prescribed Fire 

in Forest and Grassland 

Management 

Annual wildfire acreage depends on the age of the rough.
6

DISPOSE OF lOGGING DEBRIS—After harvest, 

unmerchantable limbs and stems are left either scattered 

across the area or concentrated at logging decks or 

delimbing gates, depending upon the method of logging. 

This material is an impediment to both people and planting 

equipment. If a wildfire occurs within the next few years, 

fireline construction can be severely hindered; the result 

being larger burn acreages and higher regeneration losses. 

Although not all large material will be consumed by a 

prescribed fire, what is left will be exposed so it can be 

avoided by tractor-plow operators. In stands that produce a 

large amount of cull material, the debris is often windrowed 

and burned. This practice should, however, be avoided 

whenever practical because of smoke management problems 

and the potential for site degradation. Broadcast burning is 

generally a much better alternative. If the debris must be 

piled before burning, construct round “haystack” piles when 

the debris and underlying ground are both fairly dry. This 

step will limit the amount of dirt in the pile. Piles containing 

large amounts of dirt can seldom be burned efficiently. 

They almost always smolder for long periods, creating 

unacceptable smoke problems.

In some cases, overstory trees are left during harvest 

whether as seed trees or as part of uneven-aged management 

system using single-tree or group selection. In both 

situations, the logging debris can still be burned, but you 

must take more care to protect the remaining trees.

PREPARE SITES FOR SEEDING AND 

PlANTING—Prescribed burning is useful when 

regenerating Southern pine by direct seeding, planting, or 

natural regeneration. On open sites, fire alone can prepare 

an adequate seedbed and control competing vegetation 

until seedlings become established. Even where competing 

vegetation cannot be adequately reduced by fire alone, 

it reduces the level of mechanical or herbicide treatment 

needed. Fire improves visibility so equipment operators 

can more easily see stumps of harvested trees, as well as 

any other hazards. In addition, if the area is to be bedded 

before planting, burning first consumes much of the 

debris. The result is more tightly packed beds and thus 

better seedling survival. Where herbicides are used to kill 

competition, subsequent burning will provide additional 

vegetation control. This also allows more efficient and 

easier movement of hand-planting crews. Prescribed fire 

also recycles nutrients, making them available for the next 

timber crop.

For natural regeneration, knowledge of anticipated seed crop 

and date of earliest seed fall is essential. If the seed crop is 

inadequate, burning can be postponed. Complete mineral 

soil exposure is not necessary or desirable; a thin layer of 

litter should remain to protect the soil. Generally, burning 

should be done several weeks prior to seed fall. Timing 

varies with species and locality.

Prescribed burning is also useful for regeneration of 

hardwood forests. After harvest, coppice regeneration is 

generally anchored on the top of a stump. As the sprouts 

mature, the stump rots and decay can be introduced to 

the bottom log of the new tree. Burning after harvest 

will kill basal sprouts and force new sprouts to come 

from belowground buds, particularly from roots. Sprouts 

originating from below ground are less susceptible to decaycausing fungi. In some cases where low-cost regeneration 

of pines is desired, broadcast burning can be used to control 

hardwood growth long enough to allow pines to be planted 

and survive, later becoming a mixed-species forest.

IMPROvE WIlDlIFE HABITAT—Fire is essential 

to maintain/restore certain plant communities that many 

wildlife species require. Examples include longleaf pine 

in the Coastal Plain, shortleaf pine in the Piedmont, Table 

Mountain and pitch pine in the southern Appalachians, oak 

savannas and woodlands in the Piedmont and mid-South, 

and early successional openings and native grasslands 

throughout the region. Suppression of fire in the South 

through the 20th century led to significant reduction in area 

covered by these communities. The quality and integrity of 

the remnants of these communities has been compromised 

severely. With this loss and deterioration, prevalence of 

associated wildlife species has declined precipitously 

Winter spot fire in heavy rough.

Damaging wildfire in heavy rough.
over the past several decades with several species now 

endangered or threatened. Likewise, several plants endemic 

to these communities also are now rare.

Additionally, prescribed fire improves habitat conditions 

for many wildlife species in a wide variety of vegetation 

cover types, including some that are often not considered 

with prescribed fire, including upland hardwoods and 

emergent wetlands. Fire sets back succession, consumes 

the litter layer and other dead plant material, and can 

improve nutrient availability for responding plant growth. 

Prescribed burning stimulates seed germination of many 

species and provides open conditions at ground level for 

travel, loafing, and feeding by game bird broods, rabbits, 

and ground-feeding songbirds. The responding groundcover 

provides forage, soft mast, and seed eaten by many birds, 

mammals, and reptiles. Prescribed burning also influences 

the composition and structure of cover available for wildlife. 

Timing and frequency of burning determines litter depth, the 

height and density of cover, as well as plant diversity. Thus, 

prescribed burning can be used to tailor habitat conditions 

for focal species.

Many game and non-game wildlife species benefit from prescribed fire.

MANAGE COMPETING vEGETATION—

Low-value, poor-quality, shade-tolerant hardwoods often 

occupy or encroach upon land best suited to growing 

pine. Unwanted species may crowd out or suppress pine 

seedlings. In soils with high clay content and in areas with 

low rainfall during parts of the growing season, competition 

for water, nutrients and growing space may significantly 

lower growth rates of the overstory. Furthermore, understory 

trees and shrubs draped with dead needles and leaves act 

as ladder fuels allowing a fire to climb into the overstory 

crowns. In most situations, total eradication of the 

understory is neither practical nor desirable. However, with 

the judicious use of prescribed fire, the understory can be 

managed to limit competition with desired species while at 

the same time providing browse for wildlife. Generally, a 

7

winter (dormant season) fire results in less root kill than a 

late spring or summer burn. One system recommended in 

the Mountains, Piedmont and Coastal Plain is a dormant 

season burn to reduce initial fuel mass, followed by two or 

more annual (if enough fuel is present) or biennial 

summer burns.

If not controlled, the hardwoods will form a midstory 

and capture the site once the pine is harvested. If a large 

pine component is wanted in the next rotation, these 

unmerchantable hardwoods must be removed during site 

preparation— an expensive proposition. Generally, fire is 

required in combination with other treatments involving 

heavy equipment, chemicals, or both. In many locations 

the preferred system is a combination summer burn and 

herbicide treatment. However, a relatively inexpensive 

alternative can be employed if site quality is moderate 

to poor; all residual hardwoods are felled and the area 

broadcast burned under exacting fuel and 

weather conditions.

In some cases, overstory pines or hardwoods are the 

competing vegetation that must be controlled. Restoration 

of open woodland conditions is a goal for landowners 

who prefer a diversity of sun-loving understory plants. 

Conversion of pine or hardwood forests with dense canopies 

requires removal of many trees by harvesting, chemicals, 

or, in limited cases, prescribed fire. Once the overstory 

is removed, frequent cool fires are required to maintain 

the open character of the forest and to allow desirable 

understory plants to become established. 

In upland hardwood stands, a predominantly woody 

Hardwood topkill after a winter burn.
Longleaf pine infected with brownspot needle blight. 

Photo by Ron Halstead, Halstead Forestry & Realty 

Inc., Bugwood.org

seedlings in unburned areas surrounding the burn unit. 

If reinfection occurs, additional burns may be needed. 

However, longleaf is most susceptible to fire immediately 

after it comes out of the grass stage. Therefore, a reburn 

will likely kill some seedlings, so such a decision should be 

made in consultation with experienced personnel. Your local 

State forestry office is a good place to begin.

Prescribed burning seems to reduce problems from fomes

annosus root rot. This fungal disease is less frequent 

where periodic burns have reduced the litter. Fire alters the 

microenvironment of the forest floor and perhaps destroys 

some fruiting bodies and cauterizes tree stumps.

Prescribed burning has not been shown to be effective at 

controlling disease in hardwood forests. Although little 

research has been conducted on this topic, one of the major 

diseases in hardwoods, a root-borne disease caused by 

Phytophthora cinnamomi, was not reduced by repeated 

fire in the southern Appalachian Mountains. This fungus is 

predominant in the soil and prescribed fires generally do not 

heat the soil sufficiently to lower the incidence of 

soil-borne diseases.

IMPROvE FORAGE FOR GRAzING—Prescribed 

burning improves grazing conditions by increasing the 

quality, palatability, and availability of grasses and forbs. 

Dead material low in nutrient value is removed, while new 

growth high in protein, phosphorus, and calcium becomes 

readily available. These benefits are manifested in increased 

seasonal cattle weight gains. Cattle congregate on recently 

burned areas; thus, burn location and size must be carefully 

selected to prevent overgrazing. 

understory and midstory often prevent adequate herbaceous 

groundcover to meet wildlife management objectives. In the 

Ridge and Valley of Tennessee, thinning has been shown to 

reduce canopy closure to approximately 60 percent. Lowintensity prescribed burning is then implemented during the 

early growing-season on a 2- to 3-year fire return interval 

to stimulate herbaceous understory growth and soft mast 

production, while controlling woody regeneration.

Prescribed fire is generally thought of as a silvicultural tool 

for controlling hardwoods in pine management. However, 

there is growing evidence that prescribed fire can be used 

in mature hardwood stands to control the composition 

of advanced regeneration, particularly to favor oak. Oak 

seedlings and sprouts are more resistant to topkill than 

other hardwoods and will sprout after numerous fires. This 

advantage is most important on good quality sites where 

other species, such as yellow-poplar, will grow quickly and 

outgrow the oaks. Prescribed burning can be conducted in 

these stands with little or no damage to overstory hardwoods 

but extreme caution must be used to maintain fires of 

low intensity.

In grasslands, prescribed fire in different seasons and 

at different frequencies is used as a tool to manipulate 

vegetation. Late-spring burning reduces the abundance of 

forbs and favors warm-season perennial grasses, whereas 

early-spring burning increases the abundance of many 

forbs and favors cool-season perennial grasses and sedges. 

Growing-season fires are occasionally used to increase 

species richness, with annual and perennial forbs and 

many cool-season graminoids the primary beneficiaries. 

Annual or biennial fires in any season are required to curtail 

encroachment of woody species, and infrequent burning 

(i.e., every three to four years) stimulates the expansion of 

most shrub species once they have become established 

in grassland.

CONTROl INSECTS AND DISEASE—Brownspot 

disease is a fungal infection that may seriously weaken and 

eventually kill longleaf pine seedlings. Diseased seedlings 

tend to remain in the grass stage. Control is recommended 

when more than 20 percent of the seedlings are infected 

or when some of the diseased seedlings are needed for 

satisfactory stocking. Once the seedlings become infected, 

burning is the most practical method of disease control. 

Any type of burning that kills the diseased needles without 

killing the terminal bud is satisfactory. Burning the infected 

needles reduces the number of spores available to infect 

the seedlings. Generally a winter heading fire under damp 

conditions, as exist after passage of a strong cold front, is 

best. Height growth of the seedlings often begins the first 

postfire-growing season after burning.

Reinfection usually occurs quickly if there are infected 

8
Patch-burn grazing is a system developed to reduce 

homogeneity in the pasture and create a mosaic grazing 

pattern. Under this system, approximately one-third of the 

pasture is burned each year, but cattle have access to the 

entire area. Because the animals preferentially graze in the 

burned section it is grazed intensively and the unburned 

areas are either grazed lightly or are ungrazed. At the end 

of the growing season, cattle are removed from the area. 

The following year another third of the area is burned 

and cattle are allowed back into the pasture. This pattern 

continues with the entire area burned on a 3-year rotation. 

Timing of burning should be adjusted based on vegetation 

composition. For example, bluestems, indiangrass, 

switchgrass, and eastern gamagrass respond best to 

early spring fire, while wiregrass responds best to midgrowing-season fire. The resultant grazing pattern creates 

a heterogeneous landscape, with one area heavily grazed, 

another area lightly grazed, and a third area that received 

little or no grazing.

9

Burning underbrush prior to the sale of forest products 

improves the efficiency of cruising, timber marking, 

and harvesting. Removing accumulated material before 

harvesting also provides greater safety for timber markers 

and loggers due to better visibility and less underbrush. 

The reduced amount of fuel helps offset the greater risk 

of wildfire during harvesting. Moreover, the improved 

visibility and accessibility often increase the stumpage value 

of the products. Hikers also benefit from easier travel and 

increased visibility and hunters are more likely to get a clear

shot at their quarry.

PERPETUATE SPECIES AND COMMUNITIES 

THAT REqUIRE FIRE—Many plants have structural 

adaptations, specialized tissues, or reproductive features 

that favor them in a fire-dominated environment. Such traits 

suggest a close association with fire over a very long period 

of time. Many endemics are only found the first 1 to 2 years 

after a fire. Changes in the “natural” fire pattern as a result 

of attempted fire exclusion have led to dramatic decreases in 

many of these fire-tolerant or fire-dependent species. 

Many plants, including picturesque orchids and coneflowers, 

are currently listed as threatened or endangered and are 

benefited by fire. Fire dependent and fire tolerant plants are 

found throughout the South in a variety of cover types and 

fire regimes ranging from pine forests that burn frequently 

to lowland bogs and north-facing mountain coves that burn 

very infrequently.

Early successional wildlife respond exceptionally well to 

patch-burn grazing. Game birds and songbirds nest in the 

unburned area, but raise broods and feed in the burned area 

where the structure is more favorable. 

Patch-burn grazing is applicable to areas dominated by 

native grasses as well as areas with considerable brushland 

and woodland. The entire area is fenced, quarter- or thirdsections burned each year, and cattle manage vegetation 

structure. Cattle producers who have an interest in wildlife 

should give this system serious consideration.

ENHANCE APPEARANCE AND ACCESS—

Prescribed burning improves recreation and aesthetic values. 

For example, burning maintains open stands, produces 

vegetative changes, and increases numbers and visibility 

of flowering annuals and biennials. Burning also maintains 

open spaces such as mountain balds and creates vistas. 

Unburned islands increase vegetative diversity which 

attracts a wider variety of birds and animals. A practical way 

to maintain many visually attractive vegetative communities 

and perpetuate many endangered plant species is through 

periodic use of prescribed fire.

Using fire to manage landscapes and enhance scenic values 

requires judiciously planned and executed burns, especially 

where there is considerable exposure to the public. Burning 

techniques can be modified along roads and in other heavily 

used areas to ensure low flame heights, which in turn will 

reduce visible damage to trees while still opening up the 

stand and giving an unrestricted view.

Table Mountain pine benefits from fire by opening serotinous cones and 

creating optimal seedbed habitat.
10

Prescribed burning, however, does not automatically help 

perpetuate plant and animal species because fires are not 

necessarily conducted during the same season in which the 

site historically burned. The interval between prescribed 

fires as well as fire intensity may also differ from those of 

Red-cockaded woodpeckers and smooth coneflower require the conditions created by frequent burning to survive.

the past. The individual requirements of a species must 

therefore be understood before a fire can be prescribed 

to benefit that species. In some cases, such as with Table 

Mountain pine, fire managers are only now learning the 

season and intensity of fire needed for 

successful regeneration.
Prescribed burning has direct and indirect effects on the 

environment. Proper use of prescribed fire and evaluation of 

the benefits and costs of a burn require knowledge of how 

fire affects vegetation, wildlife, soil, water, and air. Burning 

techniques and timing of burns can be varied to alter fire 

effects. 

vEGETATION

Fire effects on plants can vary considerably among fires 

and within the same fire. The degree of injury, mortality, 

and recovery of plants from fire is influenced by fire 

behavior, fire duration, season of burning, the pattern of fuel 

consumption, and the amount of subsurface heating. Postfire responses can vary by plant species because they differ 

in their ability to survive fire and their ability to regenerate

after fire. 

Most plant cells are killed if they are heated to 122—131 

o

F (50—55 oC) for a short time or they can be killed by 

exposure to lower temperatures for longer periods. Slowmoving cool fires can kill as many plants as faster-moving 

hot fires. Actively growing meristems, such as the cambium 

or buds of trees and basal meristems of grasses are most 

susceptible to heat and are easily damaged. The degree to 

which these tissues are protected by bark, scales, or soil 

determines if a plant will survive fire. Pines and some 

hardwoods have thick bark which insulates them from 

heat. Tall crowns protect buds and foliage from the heat of 

ground fires. Hardwood trees are generally more susceptible 

to fire injury than are pines because their bark is thinner. 

With the exception of Eastern white pine and Virginia pine, 

southern pines 3 inches or more in ground diameter have 

bark thick enough to protect the stems from damage by most 

prescribed fires. However, the crowns are quite vulnerable 

Most pine species are well adapted to 

frequent low-intensity fires.

Environmental Effects

11

Crown scorch can add fuels to the 

forest floor, reduce growth, or cause 

tree mortality.

Hardwood topkill.

Lethal time-temperature curve.
to temperatures above 135 °F. Pine needles will survive 

exposure to 130 °F for about 5 minutes, while similar 

needles exposed to 145 °F for only a few seconds will die. 

Crown scorch in pines does not always indicate that the 

trees will die but it usually slows growth for a year or more. 

If the duff layer is consumed, roots are frequently damaged 

which can lead to moisture stress and possibly mortality if a 

significant portion of the feeder roots die.

Larger plants are generally better protected from fire than 

smaller ones because their meristems are better protected 

by thicker bark, taller crowns, and thicker duff. Prescribed 

fires often topkill (mortality of all aboveground portions of 

the plant) hardwoods less than 6 inches dbh and pines less 

than 3 inches dbh. Prescribed burning has traditionally been 

avoided in hardwood stands because fire scars are prevalent 

and can reduce the value of crop trees. However, in recent 

years prescribed burning has been used in hardwood stands 

for site preparation, to favor establishment of oaks, enhance 

conditions for wildlife, and to restore stand structure to 

historical conditions.

Most southern pines, larger than sapling size, are able to 

tolerate a high degree of crown scorch, especially during 

the dormant season, with minimal effects on survival. Most 

pine species produce several flushes of needle growth 

during a growing season giving them the ability to leaf out 

soon after defoliation. Pines are most susceptible to scorch 

in spring when leaders are succulent but can survive after 

almost complete scorching at any other time although some 

mortality may occur. 

After prescribed fires, plants regenerate by sprouting, 

seeding, or both. Most hardwood trees and perennial 

forbs produce sprouts from buds located at or beneath 

ground level after their aboveground portions are killed by 

fire. Grasses vary by species but most sprout from basal 

meristems. Few pine species sprout. Wildfires that kill 

overstory pines and hardwoods commonly shift species 

composition from pine-dominated forests to a newly 

12

regenerated hardwood coppice forest. This can also be a 

concern when prescribed burning is used to reduce fuels in 

blow-down or beetle-killed areas. Regeneration by seed is 

also impacted by prescribed burning. Although many seeds 

on the forest floor are consumed by prescribed fire, others 

remain viable for years and are stimulated by fire. Natural 

regeneration of pines can be successful if prescribed burning 

is timed prior to a heavy seed crop. Some pines have 

serotinous cones which are stimulated to open by the heat 

of a fire. This can be successful with a properly executed 

prescribed fire. Other tree species have light or winged seeds 

which are carried by wind into burned areas. Germination 

and survival of seedlings are generally improved by 

prescribed burning due to a thinner duff layer, exposed soil, 

and increased available sunlight reaching the forest floor.

Fire affects not only individual plant species but also entire 

communities. Community structure can be managed by 

prescribed burning. For example, a single prescribed fire can 

be used to reduce the shrub layer and, if burning is frequent, 

a grass and forb layer will replace the shrubs. The absence 

of fire over time will favor more shade-tolerant and less firetolerant species.

Many benefits from prescribed fire, such as increased forage 

for grazing and improved conditions for wildlife, depend 

on changes in the vegetation. However, fire that is used 

unwisely may adversely alter plant species composition 

and structure.

SOIl

The interaction of many factors determines the impact of 

fire on soil but most evidence indicates that low-intensity 

prescribed fires have few, if any, adverse effects. Prescribed 

fires affect soil by both heat transfer and changes in soil 

physical properties. The most important soil physical 

characteristic affected by fire is soil structure because 

organic matter can be lost at relatively low temperatures. 

Loss of soil structure can increase bulk density and reduce 

porosity, thereby reducing soil productivity and making 

Burning under dry conditions can cause erosion, especially in hilly terrain.
the soil more vulnerable to post-fire runoff and erosion. 

Prescribed burning in the South normally causes little or no 

detectable change in amount of organic matter in surface 

soils. In fact, slight increases have been reported on some 

burned areas. However, burning piled or windrowed debris, 

or burning when fuel and/or soil moisture conditions are 

extremely low, may elevate temperatures long enough to 

ignite organic matter in the soil as well as alter the structure 

of soil clays.

Changes in soil fertility and nutrient content depend largely 

on organic matter because soil organic matter plays a 

key role in nutrient cycling, cation exchange, and water 

retention. When organic matter is combusted, the stored 

nutrients are either volatilized or quickly used by microbial 

organisms and vegetation. Those available nutrients not 

immobilized are easily lost by leaching or surface runoff 

and erosion. Nitrogen is the most important nutrient affected 

by fire, and it is easily volatilized and lost from the site at 

relatively low temperatures. With prescribed burning, duff 

layers should not be completely consumed, so that changes 

in soil pore space and infiltration rate are very slight. If 

mineral soil is repeatedly exposed, rain impact may clog fine 

pores with soil and carbon particles, decreasing infiltration 

rates and aeration of the soil. Soil microbial populations, 

important for decomposition and nutrient cycling, are 

resilient to fire, especially low-intensity prescribed 

fires. Recolonization to preburn levels is common when 

prescriptions that protect forest floor, humus layers, and soil 

humus are followed.

WATER qUAlITY

With prescribed burning, the principal concerns for water 

are runoff and increases in sediment, nitrate and heavy metal 

content. When surface runoff increases after burning, it may 

carry suspended soil particles, dissolved inorganic nutrients, 

and other materials into adjacent streams and lakes, thus 

reducing water quality. Prescribed fires are usually not 

severe so these effects seldom occur after Coastal Plain 

burns. On steep terrain, however, if post-fire storms deliver 

large amounts of precipitation or short-duration, highintensity rainfalls, accelerated erosion and runoff can occur 

even after a carefully planned prescribed fire. 

Rainwater leaches minerals out of the ash and into the soil. 

In sandy soils, leaching may also move minerals through 

the soil layer into the ground water. Generally, a properly 

planned prescribed burn will not adversely affect either the 

quality or quantity of ground or surface water.

A major concern of land managers is how fires affect 

surface runoff and soil erosion. On most Lower and Middle 

Coastal Plain sites, there is little danger of erosion. In the 

steeper topography of the Upper Coastal Plain, Piedmont, 

and Mountains, some soil movement is possible, but not 

typical. If the burn is under a timber stand and some duff 

remains, soil movement will be minor, much less than after 

site preparation with heavy machinery. Duff should be wet 

or damp at the time of burning to ensure that an organic 

layer will remain after a prescribed burn. Moisture not only 

protects the duff layer adjacent to the soil, but also prevents 

the fire from consuming soil humus. 

Backing fires produce less smoke than heading fires.

Protect streamside zones.

AIR

The Federal Wildland Fire Policy (U.S. Department of the 

Interior and U.S. Department of Agriculture 1995) and the 

Clean Air Act as Amended 1990 (PL 101-549) resulted 

13
in the need to significantly raise the level of knowledge 

about the effect of fire on air quality in order to meet 

regulatory and management requirements. For example, new 

information is needed to assess, monitor, predict, 

and manage:

• Emissions and air quality impacts from wildfires

• Acute health effects of human exposure to smoke

• Natural and anthropogenic sources of visibility reduction

• Cumulative air quality impacts from expanded fuel 

management programs

• Tradeoffs between air quality impacts from wildland fire 

and prescribed fire

Smoke adversely impacts air quality, particularly for two 

of the EPA’s pollutants covered by the National Ambient 

Air Quality Standards (NAAQS), PM2.5 (particulate matter 

smaller than 2.5 microns) and ozone. Wildland fires release 

significant amounts of PM2.5 and while fires do not release 

ozone, they do release various nitrogen oxides and volatile 

organic components that play a role in ozone formation. The 

EPA’s AirNow website (http://www.airnow.gov) provides 

daily estimates of the air quality as well as forecasts of 

expected changes in air quality. 

Smoke can be managed by burning on days when it will 

blow away from smoke-sensitive areas. Precautions must 

be taken when burning near populated areas, highways, 

hospitals, airports, and other smoke-sensitive areas. Weather 

and smoke management forecasts are available as a guide 

for wind speed and direction. Any smoke impact downwind 

must be mitigated before lighting the fire. All burning 

should be done in accordance with applicable smoke 

management guidelines and regulations. During a regional 

alert when high pollution potential exists, all prescribed 

burning should be postponed.

Nighttime burning should be done with additional care 

because a temperature inversion may trap smoke near the 

ground. This smoke can create a serious visibility hazard, 

especially in periods of high humidity (which occurs on 

most nights). In particular, smoke mixing with existing fog 

will drastically reduce visibility. In mountainous areas, cool 

air drainage at night will carry smoke down slopes, causing 

visibility problems in lowlands and valleys. On the Coastal 

Plain, nighttime air drainage often follows waterways. 

Conditions can be especially hazardous near bridge 

crossings because of the higher humidity there. Of course, 

the earlier in the day a fire is completed, the less likely it is 

to cause nighttime smoke problems.

HUMAN HEAlTH AND WElFARE

Occasional brief exposure of the general public to low 

concentrations of drift smoke is more a temporary 

inconvenience than a health problem. High smoke 

concentrations can, however, be a very serious matter. 

Health of all neighbors is of great concern but several 

subgroups within the population are more sensitive 

than others. Children are more likely to have decreased 

pulmonary function, while increased mortality has 

been reported in the elderly and in individuals with 

cardiopulmonary disease. Asthmatics are especially 

susceptible to smoke exposure. Great care must be taken 

with any management fire, particularly near homes of people 

with respiratory illnesses or near health-care facilities.

Prescribed burning can be used in a manner to avoid smoke 

sensitive areas. Smoke from wildfires cannot be controlled.

14

Prescribed fires may contribute to changes in air quality. 

Air quality of a regional scale is affected only when many 

acres are burned on the same day. Local problems are 

more frequent and occasionally acute because of the large 

quantities of smoke that can be produced in a given area 

during a short period of time.

Smoke consists of small particles (particulate) of ash, partly 

consumed fuel, and liquid droplets. Other combustion 

products include invisible gases such as carbon monoxide, 

carbon dioxide, hydrocarbons, and small quantities of 

nitrogen oxides. Oxides of nitrogen are usually produced at 

temperatures only reached in piled or windrowed slash or in 

very intense wildfires. In general, prescribed fires produce 

inconsequential amounts of these gases. Except for organic 

soils (which are not generally consumed during prescribed 

burns), forest fuels contain very little sulfur, so oxides of 

sulfur are rarely a problem.

Particulates, however, are of special concern to the 

prescribed burner because they reduce visibility and 

increase health risks. The amount of particulate put into 

the air depends on amount and type of fuel consumed, fuel 

moisture content, and rate of fire spread as determined by 

timing and type of firing technique used. Rate of smoke 

dispersal depends mainly on atmospheric stability and 

wind speed.
Smoke can have negative short-and long-term health effects. 

Fire management personnel who are exposed to high smoke 

concentrations often suffer eye and respiratory system 

irritation. Under some circumstances, continued exposure to 

high concentrations of carbon monoxide at the combustion 

zone can result in impaired alertness and judgment. Over 90 

percent of the particulate emissions from prescribed fire are 

small enough to enter the human respiratory system. These 

particulates can contain hundreds of chemical compounds, 

some of which are toxic. The repeated, lengthy exposure to 

relatively low smoke concentrations over many years can 

contribute to respiratory problems and cancer. But, the risk 

of developing cancer from exposure to prescribed fire has 

been estimated to be less than one in a million.

Although the use of herbicides in forest management 

has increased, all chemicals are now tested before being 

approved for use, and we are more careful than ever to 

minimize their potential danger. Many of them break down 

rapidly after being applied. Moreover, both theoretical 

calculations and field studies suggest prescribed fires are hot 

enough to destroy any chemical residues. Minute quantities 

that may end up in smoke are well within currently-accepted 

air quality standards. Threshold limit values (TLVs) are 

often used to measure the safety of herbicide residues in 

smoke. Expected exposure rates of workers to various 

brown-and-burn combinations have been compared with 

TLVs. They showed virtually no potential for harm to 

workers or the general public.

There is at least one group of compounds carried in smoke 

that can have an immediate acute impact on individuals. 

Smoke can cause skin rashes when noxious plants such as 

poison ivy burn. These rashes can be much more widespread 

on the body than those caused by direct contact with the 

plants. Wear respirators or avoid inhaling any smoke when 

burning areas where poison ivy grows.

WIlDlIFE

The major effects of prescribed burning on wildlife are 

indirect. However, a change in the structure and composition 

of vegetation impacts availability of food and cover, which 

directly influences the health, abundance, and diversity 

of wildlife. Direct mortality of wildlife from prescribed 

burning is rare. 

Prescribed burns can be scheduled during periods that are 

not critical to reproduction and survival of wildlife. For 

example, burning can be conducted outside the primary 

nesting season of focal species, and areas may be burned 

on a rotation and scale such that adequate cover is always 

available in the appropriate proximity for nesting, rearing 

young, feeding, escaping predators, and winter survival. 

Season and frequency of burning and the size of the area 

burned is crucial to the successful use of fire to improve 

wildlife habitat. A change in vegetation structure and 

composition can be good for some species and not so good 

for others. Prescriptions must recognize the biological 

requirements of focal wildlife species.

GRASSlAND BIRDS, SCRUBlAND BIRDS, 

FOREST BIRDS —Prescribed fire rejuvenates and 

maintains grassland habitat for eastern meadowlark, 

Henslow’s sparrow, grasshopper sparrow, dickcissel, field 

sparrow, and others. However, because a litter layer is 

important for some ground-nesting birds, a 2- to 3-year 

fire return interval at the end of the dormant season may be 

appropriate in such cases. Unburned habitat should always 

be present for nesting. Thus, it is important to not burn all 

available habitat in one year. 

Scrubland birds, such as indigo bunting, loggerhead shrike, 

blue grosbeak, song sparrow, common yellowthroat, 

yellow-breasted chat, and brown thrasher require some 

level of shrub component in their habitat. Dormant-season 

prescribed fire implemented on a 3- to 5-year fire return 

interval in areas that receive full sunlight will maintain a 

shrub component that attracts these birds.

Prescribed burning in a closed-canopy forest will not 

improve conditions for forest songbirds that require a welldeveloped understory, such as black-throated blue warbler, 

hooded warbler, worm-eating warbler, white-eyed vireo, and 

Kentucky warbler. However, forests with a broken canopy 

that allows more than 30 percent sunlight to reach the forest 

floor may be managed with fire to develop suitable structure. 

In these forests, dormant-season fire on a 3- to 5-year fire 

return interval will maintain a well-developed understory. 

In more open hardwood woodlands a 3- to 4-year fire 

return interval will maintain suitable habitat for northern 

flicker, red-headed woodpecker, prairie warbler, indigo 

bunting, eastern towhee, fox sparrow, chipping sparrow, and 

chestnut-sided warbler. Open pine woodlands and savannas 

should be maintained with a 2- to 3-year fire return interval 

for red-cockaded woodpecker, red-headed woodpecker, 

Bachman’s sparrow, and brown-headed nuthatch.

GAME BIRDS—The northern bobwhite is considered 

the “model” fire-adapted species. It requires frequent 

disturbance and prescribed fire is essential to promote and 

maintain suitable quail habitat. Burning in closed-canopy 

woods will not benefit northern bobwhite. Basal area of 

forested areas should not exceed 50 square feet per acre 

where the bobwhite is a focal species. Suitable cover may 

be promoted and maintained in woodlands, savannas, 

shrublands and grasslands by burning on a 2- to 5-year fire 

return interval. Alternating dormant- and growing-season 

fire will maintain structural diversity. A diverse composition 

15
of native grass, forb, and shrub cover is critical. Do not 

burn all available cover in one year, but burn on rotation so 

that cover for nesting, raising broods, and escape is always 

present in a given area.

A recently burned area is an immediate attraction for wild 

turkeys. Seeds, acorns, and invertebrates are exposed and 

made more available to foraging turkeys. Burning on a 2- to 

4-year fire return interval in pine and upland hardwoods 

that allow more than 30 percent sunlight to reach the forest 

floor will stimulate increased groundcover and soft mast 

production that will enhance conditions for nesting and 

raising broods. Early successional openings should be 

burned on a 2- to 3-year interval to provide open conditions 

at the ground level and facilitate brood use. Burning during 

the growing season in longleaf systems has been a concern 

because of potential nest destruction. However, wild turkeys 

readily re-nest, especially if the nest is disturbed during the

laying or early incubation period. Nonetheless, the overall 

benefit of habitat improvement to the population generally 

out-weighs the potential negative of losing a few nests.

Burning upland hardwoods on southern, western, and 

eastern exposures in the southern Appalachian Mountains 

can benefit ruffed grouse if adequate sunlight is available to 

stimulate understory development. Dormant-season fire on 

a 4- to 5-year fire return interval may be used to maintain 

woody stem density and brood cover. Fire consumes the 

litter layer and increases availability of mast, seed, and 

invertebrates. Early growing-season fire should not be used 

because ruffed grouse do not readily re-nest in the southern 

Appalachians.

Other game birds in the South that benefit from prescribed 

burning include the mourning dove, American woodcock, 

and Wilson’s snipe. Recently burned cut-overs and old fields 

are extremely attractive sites for doves to feed. Woodcock 

are also attracted to burned cut-overs in mid-winter as the 

mating season begins. Recently burned emergent wetlands 

are favorite spots for snipe to feed.

WHITE-TAIlED DEER—Burning in closed-canopy forest 

will do little to improve browse availability or fawning 

cover for white-tailed deer. However, pine and upland 

hardwood stands that allow >30 percent sunlight and early 

successional areas can be burned during the dormant- or 

early growing season on a 3- to 4-year fire return interval 

to increase/maintain browse, bramble, forb, and soft mast 

availability. Plants such as old-field aster, pokeweed, 

ragweed, beggar’s-lice, and blackberry are preferred foods 

for white-tails and respond well to periodic fire. Old-fields 

may be burned during the late growing season to control 

woody competition and increase forb coverage. Periodic 

prescribed fire will maintain browse species, such as 

greenbrier, blackgum, and winged elm, at a height available 

to white-tails and stimulate highly palatable and nutritious 

fresh growth. 

OTHER MAMMAlS—Prescribed burning can increase 

or maintain dense understory cover and production of soft 

mast (blackberries, blueberries, huckleberry, and pokeweed) 

that is critical for black bear. Gray and red fox, coyote, and 

bobcat are also attracted to these areas, either for soft mast 

or small mammal prey. Rabbits, groundhog, and several 

species of small mammals benefit from fresh vegetation 

arising postfire, especially where fields are adjacent to dense 

cover. Maintaining early successional openings with early 

growing-season fire on a 2- to 4-year fire return interval 

is highly recommended. Fox squirrels in pine-dominated 

systems along the Coastal Plain benefit from frequent 

growing-season fire that maintains an open understory 

and midstory.

REPTIlES AND AMPHIBIANS—Prescribed fire is 

critical to restore and maintain habitat for species endemic 

to fire prone systems, such as the indigo snake, pine snake, 

eastern diamondback rattlesnake, eastern coral snake, 

gopher tortoise, gopher frog, and pine barrens treefrog. 

In upland hardwoods, prescribed burning may lead to 

drier site conditions as the litter layer is consumed and 

overhead vegetation is removed; however, populations of 

Plethodontid salamanders have not been found adversely 

affected and lizards and other reptiles may benefit from the 

altered conditions. Infrequent burning of isolated wetlands 

or bogs helps limit encroachment by woody vegetation and 

maintains more open conditions favored by many species of 

reptiles and amphibians.

AqUATIC ORGANISMS—Prescribed fire does not 

necessarily benefit aquatic organisms, but it should not 

have adverse effects when implemented properly. Burning 

conditions are often unfavorable along riparian zones 

because of increased fuel moisture and humidity. However, 

Prescribed burning attracts wildlife. Photo by Dale Wade, Rx Fire Doctor, 

Bugwood.org

16
waterways are often used as firebreaks, and when fire 

creeps into a riparian zone, it should not cause alarm. If 

a waterway is not allowed to act as a firebreak, a plowed 

or disked firebreak should not be established adjacent to 

the waterway. An adequate buffer should be maintained 

between the firebreak and riparian zone to prevent possible 

sedimentation, which is much more likely to result from a 

plowed or disked firebreak than underburning in the riparian 

zone. Indeed, the positive effects of prescribed burning on 

vegetation and associated wildlife are just as applicable in a 

riparian zone as in the uplands.

AESTHETICS

Prescribed burning creates immediate and substantial 

changes to the appearance of Southern forests and 

grasslands, particularly if the area has not been burned in 

three years or more. Grasslands are blackened and plants 

are consumed. Forests have dead understory plants, char 

along the stems of trees, and possibly crown scorch. These 

short-term changes can be perceived as negative or positive 

depending on the values and experiences of the observer. 

Many prefer unmanaged forests and dislike widespread and 

sudden change, especially when large tracts are burned. 

Others appreciate the benefits of prescribed burning and 

are less concerned with blackened surfaces. Many people 

prefer the appearance of open forests created by repeated 

prescribed burning to forests with a dense understory that 

are burned infrequently or never.

Aesthetics and species diversity can be enhanced by 

prescribed fire.

Undesirable aesthetic impacts are relatively short term and 

can be minimized by considering scenic qualities when 

planning a burn. For example, the increased turbulence and 

updrafts along roads and other forest openings will cause 

more intense fire with resulting higher tree trunk char and 

needle scorch. 

Variety or diversity in vegetative cover can create a more 

pleasing, general visual character. Similarly, scenic qualities 

of the forest can be better appreciated if the stand can be 

made more transparent. An example is the reduction of an 

understory buildup along a forest road that will permit the 

traveler to see into the interior of the stand, perhaps to a 

landscape feature such as a pond or interesting rock outcrop. 

The smutty appearance of the ground will “green up” fairly 

quickly and burning during the growing season can help 

minimize the length of time before green-up. Any scorched 

needle will soon drop and not be noticeable. 

17

Weather and Fuel 

Considerations

INTRODUCTION

The choice of weather conditions under which a prescribed 

fire is conducted is key to controlling the fire and meeting 

the objectives of the burn. For a given site, the topography 

and fuel type/loading are generally fixed constraints, while 

the weather parameters that influence fire behavior and 

fuel moisture content are the variables that a manager can 

choose to obtain a fire of the desired intensity. The weather 

variables of primary interest for determining fire behavior 

are temperature, relative humidity, wind, rainfall and 

atmospheric stability (for smoke management considerations 

mixing height and transport winds are also relevant). Since 

weather is such a critical factor in successful prescribed 

burning one should become familiar with local weather 

patterns and develop an understanding of how the weather 

changes throughout the day for a given site. Experienced 

prescribed burners can utilize an understanding of how local 

weather and fuels interact to conduct successful prescribed 

burns even with one or more factors outside the desired 

range as long as other factors can compensate. The judicious 

burner will become familiar with the location of agency 

weather stations where data is collected so that differences 

between the agency site and the burn site can be 

mentally reconciled.

IMPORTANT WEATHER ElEMENTS

TEMPERATURE—Temperature needs to be considered for 

two reasons. First, high temperatures can damage overstory 

vegetation. The average instantaneous lethal temperature 

for living tissue is around 140 °F. Lower air temperatures 

are recommended for most prescribed burning because the 

lower the temperature, the more heat is required to raise 

foliage temperature to a lethal level. Air temperatures below 

60 °F are recommended for winter understory burning. 

If the burn objective is to control undesirable species (or 

preserving the overstory is not a concern) then growing 

season burns with ambient air temperatures of 

80 °F are recommended. How susceptible a stand is to 

temperature related damage is related to bark thickness, 

crown base height, and duration of the heat pulse.

Secondly, temperature plays a role in the moisture dynamics 

of forest fuels. For the same atmospheric moisture content, 

higher temperatures help to dry fuels more quickly. Fuels 

exposed to direct solar radiation become warmer than the 

ambient air which favors the movement of moisture from 

the warmed fuel to the atmosphere. When temperatures 

drop below freezing and liquid water in and on fuels turns 

to ice, fire intensity will be significantly lower as more heat 

is required to change ice to liquid water before it can be 

vaporized and driven off as steam. Consequently, it does 

not take much moisture at below freezing temperatures to 

produce a slow moving fire that tends to leave large 

areas unburned.

For debris burning, cleared areas are often burned with 

high ambient air temperatures as there is no overstory to 

protect. These high temperatures also frequently coincide 

with high mixing height values which can help with smoke 

dispersion. It is important to use an ignition pattern that will 

draw heat into the cleared area to help prevent heat damage 

to trees in adjacent stands. On fairly flat terrain a ring fire 

including center ignition is often used. On steep slopes, 

the upper control line is first ignited and when the fire has 

backed down hill far enough to create a substantial black 

line, the remainder is burned with strip headfires proceeding 

downhill (and igniting both flanks as you proceed) or by 

igniting the two flanks at the same time and then firing the 

bottom line. One should always bring fire down the flanks as 

the burn proceeds to help prevent slopeover. 

In mountainous terrain temperatures vary substantially with 

elevation. As a general rule the temperature decreases 

3.5 °F for every 1,000-foot increase in elevation. The 

primary exception to this rule being the occasional presence 

of a warm band part way the slope called a thermal belt. 

Most common at night, the thermal belt results when an 

inversion (a layer of air in which the temperature increases 

with height) intersects the slope. North facing slopes tend to 

be cooler than south facing slopes.

ATMOSPHERIC MOISTURE—Atmospheric moisture 

content plays a crucial role in wildland fire as it exerts the 

major influence on fine-fuel moisture content. The moisture 

content of the atmosphere can be expressed in a number 

of ways, but the most commonly used in prescribed fire is 

relative humidity. As the name implies, relative humidity 

is not an exact measure of the moisture content of the 

atmosphere, but rather a relative expression of the moisture 

content compared to the saturation value for a given 

temperature and pressure. The lower the relative humidity, 

the more rapidly fuels will dry.

19
20

The linkage of relative humidity and temperature causes 

the relative humidity to reach a daily minimum when the 

temperature peaks, generally early to mid-afternoon. As 

the temperature rises, the saturation moisture content of 

the atmosphere also increases which causes the relative 

humidity to decrease; providing the actual moisture content 

of the air stays the same. For every 20 °F increase in 

temperature, the relative humidity is decreased by half as 

long as the air mass is not replaced, such as with passage of 

a sea-breeze front. When the temperature drops by 20 °F, the 

relative humidity doubles.

This relationship holds as long as the moisture content of the 

air remains the same. When a cold front passes over an area, 

the air behind the front is cooler and drier than the old air 

mass it is replacing and both the temperature and the relative 

humidity drop. A common weather parameter useful for 

tracking such changes in moisture content is the dew point. 

The definition of dew point is the temperature to which air 

must be cooled to reach its saturation point. When the dew 

point is high there is much more water vapor in the air than 

when the dew point is low. In the case of the passing cold 

front, both the temperature and the dew point drop; and it is 

the drop in dew point that accounts for the drop in relative 

humidity behind a cold front. The dew point can provide 

additional useful information. As the definition states, when 

the air temperature approaches the dew point the air mass 

begins to saturate, leading to the formation of dew and fog. 

The preferred range in relative humidity for prescription 

burns is between 30 and 55 percent, although some 

uncommon objectives call for a relative humidity above or 

below this range. At the lower end of this range prescribed 

burning can become dangerous as fire intensities increase 

and fine dead fuels quickly dry to the point where embers 

landing outside the planned burn begin to ignite spot fires. 

In many southern states relative humidities below 30-35 

percent warrant a Red Flag Warning issued by the National 

Weather Service for potentially hazardous fire weather 

conditions. However, note that these low relative humidities 

are often measured and forecast for open areas and do 

not fully consider the presence of a tree canopy. In-stand 

humidities are often higher than in open areas due to lower 

temperatures and the tendency for fuels to dry more slowly 

under canopy. Be aware that the air above the canopy will 

have considerably lower relative humidity values which can 

be transported through the canopy by convective eddies and 

lead to erratic fire behavior. 

As relative humidity increases, less fuel will burn resulting 

in a lower fireline intensity and patchier burn; the end result 

may be a burn that did not accomplish the 

desired objective(s).

For debris burning one is normally concerned with fuels 

larger than the fine dead fuels that carry an understory 

fire. Relative humidity and temperature also influence the 

moisture content of these larger fuels but with a much 

longer time lag. Liquid moisture in the form of rainfall or 

dew can also influence fuel moisture depending upon the 

amount and duration. Recently cut pine tops have a drying 

rate that is somewhat independent of relative humidity while 

the moisture content is above 32 percent. Once the tops 

have dried past this threshold they respond to drying similar 

to other dead fuels and respond more readily to changes 

in relative humidity. The spatial arrangement of fuels is 

important in how fast they dry. Needles/leaves on elevated 

branches dry much more rapidly than those in contact with 

the litter as the damp litter layer acts as a source of moisture 

for the needles/leaves.

Daily cycle of temperature and relative humidity.
When burning debris piles, once the larger fuels ignite, 

increases in relative humidity have little impact on fire 

behavior during the active burning phase. Low humidities 

(below around 30 percent), however, will promote spotting 

and increase the likelihood of fire spreading between piles.

In mountainous areas, as with temperature, relative humidity 

is going to vary with elevation and aspect. Be aware of 

how conditions will likely change as a fire move across the 

terrain. Acceptable weather conditions/fire behavior on one 

part of the slope may lead to undesirable fire behavior 

on another.

WIND—Wind speed and direction along with topography 

control how fast and in which direction a fire will spread. 

In addition, winds play a critical role in limiting crown 

scorch by rapidly diluting the heat pulse from the fire before 

it rises through the canopy. When using backing fires, 

the combination of strong winds and cold temperatures 

protects overstory crowns from scorch; although any shift 

in wind direction is likely to produce a sudden increase in 

fire behavior. Limiting crown scorch with headfires is more 

complex as the advantage of stronger winds in reducing the 

heat pulse is offset by increases in rate of spread and 

flame length.

Two types of wind information are generally reported 

in fire weather forecasts, transport winds and surface 

winds. Transport winds are often reported as part of a 

smoke management section of a forecast and represent the 

average wind speed and direction from the ground up to the 

mixing height (more on this term later). Surface winds are 

measured 20 feet above the average height of surrounding 

obstructions, so unless burning open areas more than about 

200 feet on a side, these wind speeds have to be reduced to 

conform to in-stand conditions, the amount of the reduction 

dependent upon understory density and height and canopy 

tree density. 

some general rules of thumb are:

1) In well maintained open longleaf pine stands or other 

open stands, multiply surface wind speeds by 0.5; 

2) For more dense stands with minimal understory (those 

burned every 1-4 years), multiply surface wind speeds 

by 0.3; 

3) For more dense stands with thicker understory (those 

burned every 5-10 years), multiply by 0.2; 

4) For very dense stands and dense understory (dog hair 

stands), multiply surface wind speeds by 0.1.

Prescribed fires behave in a more predictable manner when 

the surface wind speed and direction are steady and are 

necessary to give the burner control over direction of fire 

spread on flat ground. In rough terrain, slope acts like wind 

to give a fire direction. Experienced burners sometimes 

use cross slope and down-slope surface wind directions to 

reduce fireline intensity of fires burning upslope, but this 

should not be attempted by the novice. In-stand winds of 

1 to 3 miles per hour (measured at eye level) are preferred 

for most fuel and topographic situations. For a fairly dense 

canopy this would require 20-foot wind speeds of at least 

10 miles per hour (for more open conditions a minimum 

wind speed of 6 miles per hour would be sufficient to move 

the fire). The maximum 20-foot wind speed generally 

recommended for prescribed burning is 20 miles per 

hour; although some stands can tolerate burning at higher 

wind speeds. The maximum 20 foot wind speed generally 

recommended when using a backing fire is 12-14 miles 

per hour because of fire control implications from an 

unexpected wind shift.

Winds that are consistent in direction make executing the 

burn easier and keep smoke moving as planned. Standard 

operating procedure for dormant season burns are to utilize 

west to northwest winds following passage of a cold front 

because they are generally strong and fairly consistent 

in direction as they slowly shift clockwise over the next 

few days. Prefrontal winds from the southwest are also 

reliable and are a good alternative when smoke sensitive 

areas preclude burning on northerly winds. The only caveat 

here is that the burn should be completed before the front 

passes because of the associated wind shift and likelihood 

of precipitation. If the burn is ongoing when the front 

arrives, fireline intensity will change, smoke will move 

in an unplanned direction, and precipitation will likely 

extinguish the fire thereby forcing you to return another day 

to finish the burn—not an efficient use of time and money. 

If, however, the burn is completed before precipitation 

begins, mopup is greatly facilitated. Prudent burners often 

ask for a spot weather forecast when contemplating a burn 

utilizing pre-frontal winds so ignition can be timed to ensure 

burn completion an hour or two before the precipitation is 

forecast to arrive. 

It is important to understand local factors that can lead to 

changes in wind direction such as sea and land breezes 

along the coast and winds driven by topography. The sea 

breeze is a mini front produced because land heats faster 

than nearby bodies of water, creating a thermal gradient 

that drives an onshore wind; the bigger the temperature 

difference, the stronger the wind and the farther it will 

move inland. As the sun goes down, the ground then cools 

faster than nearby water bodies and airflow reverses moving 

from land to water. Land breezes are weaker than sea 

breezes as the temperature differences are normally smaller. 

Sea breezes are typically strongest in spring when the 

temperature gradient is sharpest but they can occur any time 

of year. Sea breezes tend to cross the coast at a right angle to 

it and thunderstorms and lightning are often associated with 

the leading edge. A sea breeze can override gradient wind 

21
22

resulting in a different wind direction. Sea breeze pattern is 

consistent so local knowledge can provide the hour of the 

day it arrives at a given location; this information is used 

to determine whether a burn can be conducted before its 

arrival or to provide an ignition time if this phenomenon is 

to be used to move the smoke in that direction. In areas of 

complex topography, as the day progresses the sun warms 

different slopes/aspects at differing rates. This differential 

heating forces winds to flow upslope and up valley during 

the day with the strongest winds typically being on 

southwest facing aspects. A key feature of these locally 

driven winds is that they are just that, local phenomena. 

Local knowledge of an area will help one better understand 

these local wind patterns. Other local features to consider 

Wildfire burning under fairly steady conditions 

prior to sea breeze arrival. 

Convergence ahead of sea breeze fronts 

enhances vertical motion, making the plume 

more upright, inflows into fire increase in 

strength, feeding more oxygen into the fire. 

Potential for spotting increases. 

Small change in weather brought about just 

prior to the passage of the sea breeze front was 

enough to transition this fire from a wind driven 

fire to a plume dominated fire. 

Approach of sea breeze front can bring about rapid short term increases in fire intensity. 

Fire Smoke

Sea Breeze

Approach of sea breeze front can bring about rapid short term increases in fire intensity.
Thunderstorms are a major problem when a prescribed burn 

is in progress: 1) rain may dose the fire, 2) personnel face 

the threat of lightning and, 3) dramatic temporary changes 

in wind speed and direction will take place; thunderstorm 

downdrafts hit the ground and spread in all directions at 

speeds up to 60 miles per hour resulting in sudden changes 

in fireline intensity and direction of fire spread. Prudent 

burners try to schedule growing season burns so they will 

be completed before daily thunderstorm activity picks up. 

Thunderstorm outflows can travel long distances 

(30+ miles), particularly across the coastal plain of the 

southeast and can produce very abrupt wind shifts that can’t 

currently be forecast.

When broadcast burning heavy fuel loads in open areas 

such as logging debris, eye-level winds over about 4 miles 

per hour can create control problems if a head fire is used; 

experienced burners can often compensate for high wind 

speeds by altering planned ignition patterns. With piled 

debris, winds of 8-10 miles per hour can be tolerated, but 

relative humidities above 40 percent are desirable to reduce 

the spotting potential.

In mountainous terrain, winds typically increase with 

height in the atmosphere. Looking at a wind profile (or 

at least looking at the transport wind speed) will provide 

information on how strong the winds are above the surface. 

As elevation increases, the probability of exposure to these 

stronger winds aloft also increases.

How slope position and canopy closure influence wind speed.

ATMOSPHERIC STABIlITY AND DISPERSION—

Atmospheric stability is the resistance of the atmosphere to 

vertical motion and its primary importance for prescribed 

burning is related to fire behavior and smoke dispersion. 

A stable atmosphere typically results in poor burning 

conditions and limits formation of a well defined convective 

column thereby severely stifling vertical mixing of smoke 

through the lower atmosphere. In an unstable atmosphere, 

smoke and combustion products from a fire rapidly rise, 

forming a well defined convective column. The rising 

air strengthens indrafts into the fire which increase fire 

intensity, further strengthening the convective column. 

While these conditions are ideal for removing smoke from 

the burn site and dispersing it downwind, they often bring 

fire behavior and containment concerns such as erratic 

winds, enhanced spotting and an increased potential 

for crowning.

Inversions are very stable layers in the atmosphere that 

act as lids which severely limit vertical motion within that 

layer. The most common inversions in the southeastern 

United States are nocturnal inversions and the upper level 

inversions that often mark the top of the mixed layer. A 

nocturnal inversion forms at night as the ground cools. 

This surface cooling also cools the adjacent atmosphere 

and gradually builds an inversion at the surface. When 

the sun rises and begins heating the ground, the surface 

inversion is rapidly eroded. The mixed layer, that region 

of the atmosphere adjacent to the ground, where thermally 

driven eddies quickly mix atmospheric conditions towards 

a homogenous state, is often capped by an inversion. The 

mixing height is defined as the distance from the ground 

to the base of this inversion. Inversions act as barriers to 

23

for changing wind conditions include major changes in 

canopy density and land use, large lakes and rivers, urban 

areas, transmission line rights of way and roads.

WIND

20-FOOT WINDSPEED IS ADJUSTED TO 

MIDFLAME WINDSPEED BASED ON 

PARTIALLY 

SHELTERED 

FUELS

 UNSHELTERED 

FUELS

FULLY 

SHELTERED 

FUELS

PARTIALLY 

SHELTERED 

FUELS

 UNSHELTERED 

FUELS

 Fuel beneath 

patchy timber 

where it is not 

well sheltered

 Fuel beneath 

timber that has 

lost its foliage

 Fuel exposed 

to wind - no 

overstory or 

sparse 

overstory

 Fuel on high ridges 

where trees o!er little 

shelter from wind

 Fuel beneath standing timber at 

midslope or higher with wind 

blowing at slope

 Fuel sheltered beneath standing 

timber with foliage on at or gentle 

slope or near base of mountain with 

steeper slopes

 Fuel beneath timber near clearing 

or clearcuts
24

Smoke plume for a low intensity fire on a windy day with a stable atmosphere. Plume rises gradually and smoke is fairly 

evenly distributed between the ground and the mixing height downward of the fire.

vertical motion within the atmosphere and will therefore 

tend to limit the vertical mixing of smoke within the 

atmosphere. However, these barriers are not impenetrable. 

Smoke will continue to rise vertically as long as it is warmer 

than the surrounding air; therefore for smoke to be injected 

above the mixing height requires a fire with enough intensity 

that the ascending smoke column is warmer than the air at 

the top of the inversion. Injecting smoke above the mixed 

layer is often accomplished through aerial ignition as large 

areas can be ignited simultaneously to produce well defined 

convective columns.

The Haines Index is a stability index specifically designed 

for fire weather that ranks both the lapse rate and the 

presence of dry air aloft on scales of 1-3 and then combines 

these values to give an index value from 2 (stable and moist) 

through 6 (unstable and dry). The Haines Index is primarily 

used on wildfires to evaluate the potential for large fire 

growth (index values >=5). For prescribed fires, the Haines 

Index provides a means to evaluate the stability with an eye 

towards possible control problems as the index increases. 

For smoke management purposes the primary tools for 

understanding atmospheric stability center around the 

mixing height, transport winds and various indices derived 

from these them. Mixing height, as stated previously, is 

the height to which vigorous mixing of the atmosphere 

occurs and is often marked by the presence of an inversion. 

Transport wind is the vertically averaged wind from 

the ground up to the mixing height. A variety of indices 

(ventilation index, atmospheric dispersion index and low 

visibility risk occurrence index) combines mixing height and 

transport wind to provide an estimate of the atmosphere’s Change in temperature structure between 0700 and 1500. Strong surface 

inversion at 0700 is eroded throughout the day by surface heating 

producing an unstable layer at the surface.

ability to transport smoke. Note that the availability of the 

indices in fire weather forecasts varies as different states 

may require the use of different indices.

The Ventilation Index (VI) expresses the lower atmosphere’s 

ability to diffuse and disperse smoke and is calculated by 

multiplying the mixing height and transport wind speed. 

Care should be taken in choosing acceptable ranges for 

mixing height and transport winds. Do not consider these 

parameters independently. The VI is a handy tool to show 

whether your selected values provide an acceptable level 

of ventilation. Note that the VI is really only applicable 

far downwind of the source, once atmospheric eddies have 

mixed the smoke throughout the mixed layer.

The Atmospheric Dispersion Index (ADI) developed 

by Lavdas (1986) improves upon the VI by including 

atmospheric stability in the calculation through the use of 
Smoke plume for a high intensity fire on a windy day with an unstable atmosphere. Plume rises rapidly and penetrates 

above the mixing height. Most of the smoke is at or above the mixing height and will gradually mix back down toward the 

ground later in the day. 

Exercise caution for cases with high transport winds and 

low mixing heights as this can prevent smoke from rising 

vertically due to the plume being bent over, which can result 

in much higher than expected surface smoke concentrations. 

At the other end of the scale, be cautious of conditions with 

low transport wind speeds and high mixing heights as these 

conditions usually coincide with a very unstable 

atmosphere which can lead to erratic fire behavior and 

containment problems.

25

a surface-based climatological dispersion model. The ADI 

rates the potential impact of a pollutant source at one end 

of a 50-km rectangular control volume. Low values of ADI 

indicate poor dispersion. A doubling of the ADI implies 

a doubling of the of dispersion effectiveness. During the 

daytime, good values for prescribed burning range from 40 

to 60. Values exceeding 60 while producing good dispersion 

can be accompanied by erratic fire behavior; therefore, 

caution should be used when burning with ADI values over 

60. At night, dispersion is normally much poorer than during 

the day and is therefore generally evaluated on a separate 

scale from daytime conditions. Nighttime ADI values rarely 

exceed a value of 10.

Keep in mind that forecast mixing height and transport wind 

values are the values expected for mid-afternoon, not all 

day. The mixing height increases with heating during the 

day and as the mixing height grows a deeper layer of the 

atmosphere is considered in the calculation of the transport 

winds. After sunset the mixing height decreases fairly 

quickly. If you are starting a burn before noon, it may be a 

good idea to ask for a spot weather forecast that includes 

information on expected mixing height and transport wind 

information for mid-morning from the National Weather 

Service or other weather provider.

A special note needs to be made for evaluating nighttime 

conditions with regard to stability and the potential for fog 

(or a mixture of smoke and fog). A separate index, the Low 

Visibility Occurrence Risk Index or LVORI, combines the 

ADI with maximum nighttime relative humidity to estimate 

the likelihood of smoke or fog being reported at a roadway 

accident site (Lavdas and Achtemeier, 1995). The index 

ranges from 1 (few smoke/fog related accident occurred 

under these conditions) to 10 (majority of smoke/fog related 

accidents occurred under these conditions). It should be 

noted that the LVORI was developed using accident records 

from Florida; therefore its applicability in other regions 

may be questioned. From a meteorological perspective the 

LVORI as developed should apply for the coastal plain of 

the southeast but may not be applicable in the mountains. 

Other criteria to consider when evaluating the potential for 

fog or nighttime smoke problems include: clear skies, moist 

ground, light winds, and dew point and low temperature 

within 2 °F of each other.
26

Mixing Height (ft) 

Transport Wind Speed (mph) 

 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3500 4000 4500

4 7040 8214 9387 10560 11734 12907 14080 15254 16427 17600 20534 23467 26401

5 8800 10267 11734 13200 14667 16134 17600 19067 20534 22001 25667 29334 33001

6 10560 12320 14080 15840 17600 19360 21120 22881 24641 26401 30801 35201 39601

7 12320 14374 16427 18480 20534 22587 24641 26694 28747 30801 35934 41068 46201

8 14080 16427 18774 21120 23467 25814 28161 30507 32854 35201 41068 46934 52801

9 15840 18480 21120 23761 26401 29041 31681 34321 36961 39601 46201 52801 59401

10 17600 20534 23467 26401 29334 32267 35201 38134 41068 44001 51335 58668 66002

11 19360 22587 25814 29041 32267 35494 38721 41948 45174 48401 56468 64535 72602

12 21120 24641 28161 31681 35201 38721 42241 45761 49281 52801 61601 70402 79202

13 22881 26694 30507 34321 38134 41948 45761 49574 53388 57201 66735 76268 85802

14 24641 28747 32854 36961 41068 45174 49281 53388 57495 61601 71868 82135 92402

15 26401 30801 35201 39601 44001 48401 52801 57201 61601 66002 77002 88002 99002

16 28161 32854 37548 42241 46934 51628 56321 61015 65708 70402 82135 93869 105602

17 29921 34907 39894 44881 49868 54855 59841 64828 69815 74802 87269 99736 112203

18 31681 36961 42241 47521 52801 58081 63361 68642 73922 79202 92402 105602 118803

19 33441 39014 44588 50161 55735 61308 66882 72455 78028 83602 97536 111469 125403

Table of Ventilation Index values, red values represent poor ventilation (<25,800 sq ft per 

second), yellow values are fair levels of ventilation (25,800-38,750 sq ft per second) and green 

values are good ventilation (>38,750 sq ft per second). 

Table of Ventilation Index values, red values represent poor ventilation (<25,800 sq ft per second), yellow values are fair levels of ventilation 

(25,800-38,750 sq ft per second), and green values are good ventilation (>38,750 sq ft per second).

Mixing Height (ft) 

Transport Wind Speed (mph) 

 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3500 4000 4500

4 6 7 8 9 10 11 12 13 14 15 18 20 23

5 8 9 10 11 13 14 15 16 18 19 22 25 28

6 9 11 12 14 15 17 18 20 21 23 26 30 34

7 11 13 14 16 18 19 21 23 25 26 31 35 39

8 13 14 16 18 20 22 24 26 28 30 35 40 45

9 14 16 18 20 23 25 27 29 32 34 39 45 51

10 16 18 20 23 25 28 30 33 35 38 44 50 56

11 17 20 23 25 28 31 33 36 39 41 48 55 62

12 19 22 25 27 30 33 36 39 42 45 53 60 68

13 20 23 27 30 33 36 39 42 46 49 57 65 73

14 22 25 29 32 35 39 42 46 49 53 61 70 79

15 23 27 31 34 38 42 45 49 53 56 66 75 84

16 25 29 33 37 41 44 48 52 56 60 70 80 90

17 27 31 35 39 43 47 51 56 60 64 74 85 96

18 28 33 37 41 46 50 54 59 63 68 79 90 101

19 30 34 39 44 48 53 57 62 67 71 83 95 107

Table of average ADI values for moderately unstable conditions, red values represent poor 

dispersion (<=20), yellow values are fair dispersion (21-40) and green values are good dispersion 

(>40). The ADI is a function of stability and this table only shows ADI values assuming a 

moderately unstable atmosphere. If actual conditions are more stable (or unstable) the actual 

ADI values would be lower (or higher) than those in the table. If available fuel load exceeds 

about 3 tons/acre and burn unit size is more than a couple of acres, only burn when the forecast 

ADI is in the green zone 

Table of average ADI values for moderately unstable conditions, red values represent poor dispersion (<=20), yellow values are fair dispersion 

(21-40), and green values are good dispersion (>40). The ADI is a function of stability and this table only shows ADI values assuming a 

moderately unstable atmosphere. If actual conditions are more stable (or unstable) the actual ADI values would be lower (or higher) than those 

in the table. If available fuel load exceeds about 3 tons/acre and burn unit size is more than a couple of acres, only burn when the forescast 

ADI is in the green zone.

For debris burning, strong convection over cleared areas 

burned for site preparation of slash disposal helps vent 

smoke into the upper atmosphere. A convection column 

will continue to rise until it cools to the temperature of the 

surrounding air or encounters a sufficiently strong inversion 

layer. A strong convection column also forms surface 

level indrafts that help confine the fire to its prescribed 

area and allow burn crew to clearly see along control lines 

and quickly attack any slopovers. Be on the alert for large 

pieces of burning fuel sucked into the column that are still 

smoldering when they drop to the ground at some distance 

downwind; burning with relative humidity above 45 percent 

will virtually eliminate this potential problem unless the 

material is still flaming.
Atmospheric Dispersion Index (ADI)

RH 1 2 3-4 5-6 7-8 9-10 11-12 13-16 17-25 26-30 31-40 > 40

< 55 2 2 2 2 2 2 2 2 2 2 1 1 

55-59 3 3 3 3 3 2 2 2 2 2 1 1 

60-64 3 3 3 3 3 3 2 2 2 2 1 1 

65-69 4 3 3 3 3 3 3 3 3 3 3 1 

70-74 4 3 3 3 3 3 3 3 3 3 3 3 

75-79 4 4 4 4 4 4 4 4 3 3 3 3 

80-82 6 5 5 4 4 4 4 4 3 3 3 3 

83-85 6 5 5 5 4 4 4 4 4 4 4 4 

86-88 6 6 6 5 5 5 5 4 4 4 4 4 

89-91 7 7 6 6 5 5 5 5 4 4 4 4 

92-94 8 7 6 6 6 6 5 5 5 4 4 4 

95-97 9 8 8 7 6 6 6 5 5 4 4 4 

> 97 10 10 9 9 8 8 7 5 5 4 4 4 

Table of LVORI values as a function of Atmospheric Dispersion Index and Relative Humidity. Green = conditions 

with lowest proportion of accidents. White = proportion of accidents increased by a factor of 2-10 over green. 

Yellow= proportion of accidents increased by a factor of 10-40 over green. Orange = proportion of accidents 

increased by a factor of 40-150 over green.

Whenever a burn is conducted in mountainous terrain, 

diurnal slope winds must be considered. As soon as the 

slope is heated by the morning sun, an upslope breeze 

results which will increase in strength into the early 

afternoon. Igniting a fire at the base of the slope during the 

day will allow the heat of the fire to work with the heated 

slope to provide extra lift to the smoke, increasing chances 

of venting smoke above the mixed layer but be exceeding 

cautious when contemplating this tactic because fireline 

intensity will continue to rapidly increase until the crest/

ridgeline is reached generally resulting in crown scorch, 

bole damage and containment problems unless the control 

line is located 50-100 feet downhill over the ridge. At night 

surface cooling drives wind and residual smoke downslope 

as mentioned above, concentrating smoke in low 

lying areas.

Visual Indicators of Atmospheric Stability

Stable Unstable

Clouds in layers, stratus type clouds Clouds grow vertically, cumulus type clouds

Smoke columns drift apart after limited rise Smoke columns rise to great heights

Poor visibility due to haze or smoke Good visibility

Fog Dust devils and firewhirls form

Steady winds Gusty surface winds

When using aerial ignition techniques at the high end of 

the prescription window it is possible to ignite too much 

area too quickly; which can combine with an unstable 

atmosphere to enhance spotting, crowning and other 

indicators of erratic fire behavior. The prudent burn boss 

will temporarily halt ignition and assess behavior of the first 

row or two of spot fires before deciding whether to adjust 

ignition pattern, change firing technique, terminate the burn, 

or continue as planned.

RAINFAll AND DROUGHT—Rainfall prior to a 

prescribed burn is extremely important as it affects both 

fuel moisture and soil moisture. Damp soil protects tree 

roots and microorganisms. Even when burning to expose a 

mineral soil seedbed, it is desirable to leave a thin layer of 

organic material. Burning should cease during periods of 

27
28

KBDI and Prescribed Fire Guidelines 

KBDI 

Range 

Notes 

0-100 Conditions generally so wet fires will go out 

Too wet to accomplish most prescribed burn objectives 

100-

200 

Marginal conditions for most understory burns. 

100- and 1000-hour fuels do not contribute to fire intensity. 

Most soil organic material, duff and lower litter layers left intact. 

Some re-ignition likely needed for burns to meet objectives. 

Good range for re-introductory fires after long periods of exclusion. Minimal mopup 

required. 

Smoke management focused on the period of the burn as little smoldering is expected. 

Any depression likely to stop fire spread resulting in patchy burns. 

Natural features such as creeks are effective control lines. 

Fires can still be quite intense as KBDI is not an indicator of 1- and 10-hour fuel 

moisture contents. 

200-

400 

Lower litter and duff layers begin to show signs of water loss and contribute to fire 

intensity. 

Expect an overall increase in fuel consumption. 

Smoldering more of a concern for smoke management as larger fuels are more likely to 

ignite and duff/litter layers may also contribute to residual smoke. 

Evaluate all line conditions, especially any natural barriers. Ensure that lines are clear of 

debris that would allow the fire to creep across. 

400-

500 

Most likely in late summer/early fall (Florida with its summer rainy season being one 

exception). 

Very intense fires are likely in this range. 

Most duff and litter will be consumed, exposing mineral soil in many cases. 

Where duff is colonized by feeder roots expect increasing damage. 

Consider postponing burns where a duff layer is present. 

Mortality should be expected from fire as Index approaches 500. 

Less residual smoke because less moisture in fuel allows more flaming consumption 

and thus 

 less smoldering after passage of flame front. 

All but the largest dead fuels will be consumed. 

Long term smoldering will contribute to smoke management problems. 

Control problems from spotting are likely. 

Live fuel moistures will drop making ignition of understory vegetation easier. 

500-

600 

Transition to extreme fire behavior conditions 

Significant tree mortality should be expected where duff is present. 

Most components of the fuel bed will burn intensely 

Stop all prescribed fire activity 

Expect all fires to harm the ecosystem 

Rest crews for wildfire suppression. 

Limit annual leave to family emergencies 

600- Expect extensive overstory mortality in all species except pond pine & Melaleuca. 
prolonged drought (KBDI [see below] above 450 on all but 

sandy sites with well-maintained longleaf where cutoff is 

around 550 – consult with local forestry agency for more 

area specific thresholds) and resume only after a soaking 

rain of at least 1 inch. When the KBDI is below these 

threshold levels a quarter to half inch of rain followed by 

sunny skies, brisk winds and low humidity will generally 

result in several days of good prescribed fire conditions with 

adequate soil and feeder-root protection.

On clay soils, such as found in the piedmont, much of 

the rainfall is lost through runoff, and duration is more 

important than amount. An inch of rain occurring in half 

an hour will not produce the same soil moisture benefits as 

a half inch of rain over a two hour period. Even on sandy 

Coastal Plain sites, small diameter fuels less than 1⁄2 inch 

in diameter will become saturated after just a few minutes 

of rain, but logs larger than 3 inches in diameter require a 

soaking rain lasting several hours to approach saturation.

DEBRIS BURNING—Generally rain has a greater impact 

on fuel moisture in cleared areas than under a canopy as no 

rain is lost to interception by the canopy. However, fuels 

in the open also tend to dry faster due to direct exposure to 

sunlight and higher wind speeds. Burn cleared areas after 

a hard rain while fuels in surrounding forested areas are 

still damp. Mountain burners often ignite open areas while 

adjacent timbered areas still have a blanket of snow. When 

burning cleared areas, soil damage is as much a function 

of fire intensity and duration as it is soil moisture. Intense, 

long duration fires will bake the soil regardless of the 

moisture present at ignition. Both the chemical and physical 

properties of the soil can be altered. Undesirable fire effects 

are often produced when burning windrowed or piled debris 

which is one reason that windrowing slash prior to burning 

is not recommended; piles, if constructed, should be less 

than 10-12 feet in diameter and piled using a root rake when 

both soil and fuel are dry.

The Keetch-Byram Drought Index (KBDI) is one tool 

available for assessing soil/duff moisture conditions. The 

KBDI is based on the notion that the upper soil and duff 

layer have a moisture capacity of eight inches at saturation. 

At saturation the KBDI has a value of zero, reflecting zero 

moisture deficit. A KBDI of 800 reflects a moisture deficit 

of 8 inches or a complete lack of moisture in the theoretical 

soil layer. The KBDI is designed to be easily calculated and 

only requires information on mean annual rainfall, daily 

rainfall and maximum daily temperature. 

Care should be taken in interpreting KBDI values as fire 

behavior can differ for a given value of the index. For 

example, a value of 400 can indicate a prolonged period of 

drying during which the Index has steadily increased which 

indicates that an intense burn may cause some feeder-root 

damage. However, a value of 400 can also be achieved by 

having received over an inch of rain when the KBDI was 

around 500. In the case where a KBDI of 400 was achieved 

through a rapid drop due to heavy rains, a brief window 

of adequate soil moisture for burning may occur, provided 

there are only 1-2 large (3+ inches in diameter) down logs 

or stumps per acre. These larger fuels may appear wet on 

the surface, but they are dry in the middle and if the fire gets

through this moist layer, the fuels will ignite and smolder for 

days creating horrendous smoke management problems.

Information on the KBDI can be obtained from local state 

forestry agencies. Note that since the KBDI depends on 

rainfall information there can be a great deal of spatial 

variability in the value over short distances when areas have 

been experiencing isolated to scattered shower activity.

Precipitation and drought conditions after the burn should be 

considered as well as conditions leading up to the burn. Fire 

is a stress on the stand and additional stress in the form of 

drought after a burn can seriously damage a stand. Consult 

long range (seasonal) weather forecasts available from the 

National Weather Service or state forestry agency to assess 

the potential for below normal rainfall over the next 

few months.

FUEl CONSIDERATIONS—Fine fuel moisture is 

strongly influenced by rainfall, relative humidity and 

temperature. The preferred range in fine fuel moisture of 

the upper litter layer (the surface layer of freshly fallen 

needles and leaves) is from 8 to 15 percent. This range 

is deliberately conservative and broad to encompass a 

wide range of ecosystems. When fine fuel moisture levels 

reach around 7 percent damage to plant roots and soil is a 

possibility and postponing the burn should be considered 

as spot fires will become problematic and fire control will 

be a major issue. Moisture levels exceeding 16 percent in 

hardwood stands and 20 percent for conifers can result in 

overly patchy, incomplete burns that do not accomplish the 

desired objectives. However, such high fuel moisture levels 

can be desirable for heavy fuel loads to keep fire intensity 

manageable, especially if aerial ignition is to be used. Note 

that fine fuel moisture levels obtained from the National Fire 

Danger Rating System (NFDRS) or fire behavior tables tend 

to be lower than actual values as they reflect worst 

case conditions.

Some experienced practitioners can accurately estimate fuel 

moisture by examining a handful of litter or bending pine 

needles into loops to see if they snap, but the only accurate 

means of getting at the fuel moisture content is by oven 

drying samples (though this is not operationally practical). 

Fuel moisture sticks that respond to weather changes like 

29
30

Source: http://weather.gfc.state.ga.us/Info/FineFuelMoistureTable.pdf

ten hour fuels are also a viable option provided they are 

placed correctly and properly maintained. Digital lumber 

moisture probes (available from most forestry suppliers) 

may be used to estimate the moisture content of fuels; 

however, it is important to test the instrument before hand 

by comparing its estimates to fuel sticks, NFDRS values or 

oven dried samples. NFDRS values can be used as long as 

their underestimation is taken into account.

The lumber probe is recommended as it is fairly accurate 

and can be used to determine the moisture content of various 

fuels. Litter moisture content can be estimated collecting a 

handful of surface litter (wear a glove), crumple it to get 

Errata: Due to errors, this table was replaced on July 1, 2013. 

FINE-FUEL MOISTURE CONTENT TABLE

REFERENCE FUEL MOISTURE

DAY TIME 8:00 AM - 8:00 PM NIGHT TIME 8:00 PM - 8:00 AM

RELATIVE HUMIDITY % RELATIVE HUMIDITY %

Dry Bulb 

Temperature 

(

o

F)

30

|

34

35

|

39

40

|

44

45

|

49

50

|

54

55

|

59 

60

|

64

65

|

69

70

|

74

75

|

79

80

|

84

85

|

89

30

|

34

35

|

39

40

|

44

45

|

49

50

|

54

55

|

59 

60

|

64

65

|

69

70

|

74

75

|

79

80

|

84

85

|

89

30-49 5 6 7 7 7 8 9 9 10 10 11 12 7 8 9 9 11 11 12 13 14 16 18 21

50-69 5 6 6 7 7 8 8 9 9 10 11 12 6 8 8 9 10 11 11 12 14 16 17 20

70-89 5 5 6 7 7 8 8 8 9 10 10 11 6 7 8 9 10 10 11 12 13 15 17 20

90-109 4 5 6 7 7 8 8 8 9 10 10 11 6 7 8 9 9 10 10 11 13 14 16 19

NOV. DEC. JAN. FEB. MAR. APR

 AUG. SEP. OCT.

MAY JUNE JULY ALL MONTHS

Daytime 8AM - 8PM Daytime 8AM - 8PM Daytime 8AM - 8PM NIGHTTIME

8→ 10→ 12→ 2→ 4→ 6→ 8→10→ 12→ 2→ 4→ 6→ 8→ 10→ 12→ 2→ 4→ 6→ No adjustment needed 

Exposed – < 50 percent shading of surface fuel

5 4 3 2 4 5 4 2 1 1 2 4 3 1 0 0 1 3

Shaded – ≥50 percent shading of surface fuel

5 5 5 5 5 5 5 4 4 4 4 5 4 4 3 3 4 5

These content tables will provide a close estimate of the fine dead fuel moisture on your burn unit 

based on RH and temperature with adjustments based on season, time of day, shading, and a southern 

correction factor. Simply take on-site temperature and RH observations and use the top part of the 

content table to find the reference moisture and record it. Then go to the next heading and select the 

month, time of day, and amount of shading to find the adjustment value and add this number to the 

reference moisture you recorded. These content tables are based on Rothermel, R. 1983. How to 

predict the spread and intensity of forest and range fires. U.S. Department of Agriculture Forest 

Service Gen. Tech. Rep. INT-141, with adjustment values for South aspect, 0 slope. 

In the southern United States, add 2 to the adjusted value if that number is 10 or more and add 1 if 

the adjusted value is less than 10 to arrive at a more accurate estimation.

Example: It is 11:30 am on December 16th and you just took on-site observations of 69 percent RH 

and 72°

F temperature in open flatwoods with 30 percent canopy cover on a cloudless day. Your 

reference moisture is thus 8. The adjustment value for 11:30 am in December is 4, which gives you 8 

+ 4 = 12. Then add the southern correction value of 2 because the adjusted value is more than 10 to 

arrive at a fine fuel moisture content of 14 percent. 
rid of air spaces and stick it with the probe; take several 

samples including lower litter/upper duff. Use the probe 

consistently to build a mental database of the affect that 

estimated fuel moisture content (using the probe) has on

fire behavior.

Do not just check the moisture condition of the upper litter/

duff but also check lower layers as well. Dry conditions 

in the lower litter/duff often follow prolonged drought 

periods (high KBDI values). Fires following prolonged dry 

periods can often burn with unexpected intensity. When 

burning on organic soils, this phenomenon can have drastic 

consequences. If the fire dries the moist surface layer of 

litter/duff, the underlying organic layer can ignite; leading 

to a fire with the potential to smolder for weeks is spite of 

control efforts, causing extensive smoke problems.

The prudent burner checks the moisture condition of the 

upper litter in sun and shade as well as the duff layer if 

present, and dead logs of various sizes. Dry conditions in 

the lower litter/duff often follow prolonged drought periods 

(high KBDI values); and once the damper surface litter is 

ablaze, these lower layers will likely burn with unexpected 

intensity and undesirable results such as feeder root damage. 

When burning on organic soils, this phenomenon can have 

drastic consequences. If the fire dries the moist surface 

layer of litter/duff, the underlying organic layer can ignite; 

leading to a fire with the potential to smolder for weeks is 

spite of control efforts, causing extensive smoke problems. 

Once ignited, organic soil requires vast amounts of water to 

extinguish. These soils are consumed through smoldering, 

not flaming, combustion and often show little evidence that 

they are burning at first as the horizontal rate of spread for 

organic soil fires is measured in inches per hour. Extensive 

smoke problems are almost guaranteed when organic soils 

are involved; therefore burning in areas with organic soils is 

not recommended for the novice burner; consult with your 

local forestry agency.

How fuels respond to changes in relative humidity is a 

complex process that depends on fuelbed characteristics 

and recent weather conditions. Different fuel types can 

reach different fine fuel moisture levels under the same 

humidity conditions. Because of these complexities and 

natural variability across a landscape, recommended 

fine fuel moisture values are only guidelines. On-theground knowledge of fuels must be incorporated into the 

prescription.

Fuel moisture influences smoke production. Damp fuels 

release large amounts of dense white smoke, which is 

mostly condensed water vapor. These water droplets are 

very efficient at scattering light and thereby 

reducing visibility.

For most prescribed fires the preferred fine fuel moisture 

8 to 15 percent.

Harvested areas should be burned when dry as the object 

is to consume large fuels. They will ignite easier, burn 

more quickly and completely, shortening the time needed 

to complete the burn. Aggressive firing techniques such 

as aerial ignition or ground ignition using a ring fire with 

center ignition as well should be strongly considered. 

Often less mopup is required and the impact on air quality 

is reduced. Short but severe drought periods common 

during the summer in the southeast provide ideal burning 

conditions on cleared areas, provided soil moisture levels do 

not get too low and the fire can be confined to the burn unit. 

To avoid damage to the site, do not windrow harvest debris. 

Consider burning debris as it lies (broadcast burned), 

although constructing small circular piles with a root rake 

when the debris has had time to cure (it won’t dry well when 

Moisture of 10-hour fuels can be measured with fuel 

moisture sticks.

31

Effects of humidity and days since rain on fine-fuel moisture.
32

piled) and when the fuel and ground is dry to minimize soil 

in the piles, will result in much better consumption of larger 

fuels. It takes a month or two after cutting for the severed 

tops to cure. Once the needles turn a greenish-yellow and 

hardwood leaves have withered, the debris is ready to burn.

Because fuels on logged areas receive full solar radiation, 

they dry more quickly than the surrounding forested area 

so once fully cured, burning can be safely done shortly 

after a rain. For slash fuels, ten hour fuel moisture values 

(fuels 1⁄4 to 1 inch in diameter, such as small branches and 

stems) are a better indicator of burning conditions than 

fine fuel moisture. Fuel moisture sticks will generally give 

excellent results. Place one set of sticks in the area to be 

burned and another in the adjacent forested area. Allow the 

sticks to acclimate for at least two weeks. The logged area 

is considered ready to burn when the moisture content is 

around 10 percent, provided the forest area is still above 

15 percent.

If larger fuels need to be consumed (those over 2 to 3 

inches), piling will probably be necessary. Piling in wet 

weather should be avoided. Keep the piles small and free of 

dirt. Allow fresh logging debris to cure for several weeks 

before piling because drying conditions within the piles are 

extremely poor. Much of the smoke problems associated 

with burning piled debris is caused by the inefficient 

combustion of damp, soil-laden piles. These piles can 

smolder for weeks.

Fine fuel moisture values can be used to estimate the 

probability ignition to help the practitioner better understand 

the potential for embers igniting spot fires outside of the 

burn unit. Probability of ignition is determined using 

the table above which requires the fine fuel moisture, 

temperature and percent shading of the fuels (shading 

includes shade from both canopy and clouds).

Probability of Ignition 

Shading Fine Dead Fuel Moisture (percent)

(percent)

Temp

° F 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

110+ 100 100 80 70 60 60 50 40 40 30 30 20 20 20 20 10

100-

109 100 90 80 70 60 60 50 40 40 30 30 20 20 20 10 10

90-

99 100 90 80 70 60 60 40 40 30 30 30 20 20 20 10 10

80-

89 100 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10

70-

79 100 80 70 60 60 50 40 40 30 30 20 20 20 10 10 10

60-

69 90 80 70 60 50 50 40 30 30 20 20 20 20 10 10 10

50-

59 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10

40-

49 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10

Unshaded

< 50%

30-

39 80 70 60 50 50 40 30 30 20 20 20 10 10 10 10 10

110+ 100 90 80 70 60 50 50 40 40 30 30 20 20 20 10 10

100-

109 100 90 80 70 60 50 50 40 30 30 30 20 20 20 10 10

90-

99 100 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10

80-

89 100 80 70 60 60 50 40 40 30 30 20 20 20 10 10 10

70-

79 90 80 70 60 50 50 40 30 30 30 20 20 20 10 10 10

60-

69 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10

50-

59 90 80 70 60 50 40 40 30 30 20 20 20 10 10 10 10

40-

49 90 80 60 50 50 40 30 30 30 20 20 20 10 10 10 10

Shaded

> 50%

30-

39 80 80 60 50 50 40 30 30 20 20 20 10 10 10 10 10
DUFF MOISTURE —Owing to the potential for prolonged 

emissions and severe fire effects from the smoldering 

combustion of organic soils and mineral soils with thick 

organic horizons, organic soil moisture is an important 

management concern for fire practitioners. The Estimated 

Smoldering Potential provides fire practitioners a means 

to assess the likelihood of sustained smoldering in organic 

soils that possess mineral content less than 10 percent.

Burning in areas with organic soils is beyond the skills/

experience of the novice burner; consult with local forestry 

agency in both the planning and execution of the burn 

to help insure that these soils do not ignite. Estimated 

smoldering probabilities should be 30 percent or less and the 

water table should be at the surface.

COllECTING AND USING WEATHER 

INFORMATION ON THE BURN

Knowledge of the weather is the key to successful 

prescribed burning, and is mandatory for proper smoke 

management. Weather information is included in the 

prescription to help define the fire behavior best suited for 

accomplishing the burn’s objectives. In preparing for the 

burn it is vital to monitor weather forecasts to ensure that 

weather elements will be within prescription and during 

the burn weather conditions should be monitored to verify 

that conditions remain within prescription. Remember to 

document all weather observations as an important part 

of the burn process as this information can be valuable in 

evaluating burn objectives and fire effects. These records 

can also aid in refining future prescriptions. They should be 

stored along with the unit prescription as vital documents. 

Routine weather observations should be made at the burn 

site before, during and after the fire. Such observations are 

important as they serve as a check on the applicability of 

the weather forecast and help keep the burn crew apprised 

of any local weather influences or changes. Also, keeping 

good weather observations during the fire is essential to 

understanding the fire impacts during post-fire monitoring. 

Make observations at hourly intervals and whenever 

changes in fire behavior are noticed. Take measurements 

in the burn unit or in fuels adjacent to the unit if heat from 

the fire may influence the readings. Measurements taken 

in open areas and within a stand are likely to be different. 

Observations can be made using a belt weather kit, digital 

handheld instruments (Kestrels as an example) or a portable 

weather station. If using a handheld digital instrument or 

portable weather station it is critical that the instruments be

calibrated on a regular basis as prescribed by 

the manufacturer.

Estimated Smoldering Potential (ESP) of root mat soils expressed as a 

percent based on soil moisture and mineral content.

Standard belt weather kit.

Kestrel pocket weather meter.

Weather forecasts are a critical part of the prescribed 

burning process and can be obtained from the National 

Weather Service (NWS), State forestry agencies, or private 

weather forecasting services. It is important to get a fire 

weather forecast and not the common public forecast 

provided through the local media as the public forecast will 

lack the detailed information needed for a prescribed burn, 

particularly smoke management information such as mixing 

height and transport winds. The contents of fire weather 

NWS forecasts can vary by office as the contents of the 

forecast are typically agreed upon by local land management 

agencies and NWS as part of a fire weather operating plan. 

This plan will contain information on the types of forecasts 

33
34

issued and their contents as well as criteria for issuing fire 

weather watches and red flag warnings.

The basic types of fire weather forecast products issued by 

NWS include a general fire weather forecast, site specific or 

spot forecasts, smoke management forecasts and fire danger 

forecasts. The general fire weather forecast is issued each 

morning and will be your primary source of information. A 

spot forecast is a special forecast issued for a specific burn 

location and requires contacting the local NWS office. This 

forecast will contain more detail than the general forecast; 

but this level of detail requires more work by the forecaster 

and should only be used when the general forecast indicates 

borderline conditions for your burn that could present a 

safety hazard or your local observations/knowledge have 

shown you that the general forecast is typically a poor fit 

for your location. Smoke management forecasts provide 

additional information on mixing height, transport winds 

and other indices such as ventilation index, dispersion index 

and low visibility occurrence risk index. 

Fire weather watches and redflag warnings are also products 

geared toward wildfire preparedness and are issued when 

high winds and low relatively humidity are both in the 

forecast. Land management agencies respond by having 

extra suppression resources on standby, and by being extra 

alert for extreme fire behavior while making initial attacks.

Document all weather observations and fire behavior at the 

time of the reading as this information can be valuable in 

evaluating burn objectives and fire effects. These records 

can also aid in refining future prescriptions.

Smoke column showing winds changing with height, which can indicate a 

potential wind shift.
BACkING FIRE

A backing fire is started along a baseline (anchor point), 

such as a road, plow line, or other barrier, and allowed to 

back into the wind. Variations in wind speed have little 

effect on the rate of spread of a fire burning into the wind, 

although some wind is necessary. Such fires proceed at a 

speed of 1 to 3 chains per hour. Backing fire is the easiest 

and safest type of prescribed fire to use, provided wind 

speed and direction are steady. It produces minimum scorch 

and lends itself to use in heavy fuels and young pine stands.

Major disadvantages of a backing fire are the slow progress 

of the fire and the increased potential for feeder-root damage 

Flame dimensions for a wind driven fire.

Backing fire technique.

GENERAl

Various firing techniques can be used to accomplish a 

burn objective. The technique chosen must be correlated 

closely with burning objectives, fuels, topography, and 

weather factors to prevent damage to forest resources. The 

proper technique to use can change as these factors change. 

Atmospheric conditions should be favorable for smoke to 

rise into the upper air and away from smoke-sensitive areas 

such as highways, airports and urban areas.

Based on behavior and spread, fires either move with the 

wind (heading fire), against the wind (backing fire), or at 

right angles to the wind (flanking fire). The movement of 

any fire can be described by these terms. For example, a spot 

fire would exhibit all three types. Heading fire is the most 

intense because of its faster spread rate, wider flaming zone, 

and longer flames. Backing fire is the least intense, having a 

slow spread rate regardless of wind speed. This type of fire 

has a narrow flaming zone, and short flames. Flanking fire 

intensity is intermediate. The slope of the land has an effect 

on rate of spread similar to that of wind. Fires behave as 

heading fires as they travel up slopes and as backing fires as 

they travel down slopes.

If you encounter slight variations in fuel volumes or 

weather conditions, consider combining two or more firing 

techniques to achieve the desired result. A solid line of 

fire always spreads faster and thus builds intensity quicker 

than does a series of spot ignitions spaced along the same 

line. Intensity increases abruptly when two fires burn 

together. The magnitude of this increase is greater when 

fires converge along a line rather than along a moving point. 

The line of crown scorch often seen paralleling a downwind 

control line delineates the zone where a heading fire and a 

backing fire meet. Fires build in intensity for a period after 

being set, particularly when moving upslope. Intensity can 

be controlled, to some degree, by setting spots or lines next 

to heavy fuels before the fire gathers intensity. However, 

safety of the ignition crew is of primary concern.

Residence time is the time it takes the flaming zone to 

move past a given point. The residence time of heading and 

backing prescribed fires is often about the same because 

the deeper flame depth of a heading fire compensates for 

its faster movement. Generally, backing fires consume 

more forest floor fuels than do heading fires. The total heat 

applied to a site may be roughly equal for both heading and 

backing fires, as long as additional fuels are not involved. 

This result can be expected even though the fireline intensity 

of the heading fire would be greater. In a backing fire, the 

released heat energy is concentrated closer to the ground.

FIRING TECHNIqUES

35
36

with increased exposure to heat if the lower litter is not 

moist. When a large area is to be burned, it often must 

be divided into smaller blocks with interior control lines 

usually every 5 to 15 chains (hand or harrowed lines). All 

blocks must be ignited at about the same time to complete 

the burn in a timely manner. In-stand winds of 1 to 3 miles 

per hour at eye level are desirable with backing fires. These 

conditions dissipate the smoke and prevent heat from rising 

directly into tree crowns.

When the relative humidity is low, a steady wind is 

blowing, and fuels are continuous, an excellent burn can be 

anticipated once the fire backs away from the downwind 

control line. Under such conditions, however, extra care 

must be taken to make sure the initial fire does not spot 

across the line.

factors associated with backing fires:

• Must be ignited along the downwind control line. 

• Use in heavy roughs.

• Use in young stands (minimum basal diameter of 3 inches 

for pine) when air temperature is below 45 °F. 

• Normally result in little scorch.

• Costs are relatively high because of additional interior 

plow lines and extended burning period resulting from 

slower movement of the fire. 

• Not flexible to changes in wind direction once interior 

lines are plowed. 

• Requires steady in-stand winds (optimum: 1-3 miles 

per hour). 

• Will not burn well if actual fine-fuel moisture is above 

20 percent. 

• Requires good fuel continuity to carry well. 

• A single torch person can progressively ignite lines. 

STRIP-HEADING FIRE

In strip-headfiring, a series of lines of fire are set 

progressively upwind of a firebreak in such a manner that 

no individual line of fire can develop to a high energy level 

before it reaches either a firebreak or another line of fire. A 

backing fire is generally used to secure the base line and the 

remainder of the area then treated with strip-heading fires. 

Strips are often set 1 to 3 chains apart. The distance between 

ignition lines is determined by the desired flame length. 

Much experience is required to predict the relationship 

between strip width and flame length.

This distance can be varied within a fire to adjust for slight 

changes in topography, stand density, weather, or the type, 

amount or distribution of fuel.

Strip-heading fire technique.

Ignition can be done with a helicopter on large areas or with drip torches on smaller areas.
FlANkING FIRE

The flanking-fire technique consists of treating an area 

with lines of fire set directly into the wind. The lines 

spread at right angles to the wind. This technique requires 

considerable knowledge of fire behavior, particularly if used 

by itself. It is used quite often to secure the flanks of a stripheading fire or backing fire as it progresses. It is sometimes 

used to supplement a backing fire in areas of light fuel or 

under more humid weather conditions. It is useful on a small 

area or to facilitate burning a large area in a relatively short 

time when a strip-heading fire would be too intense.

Flanking fire technique.

Compensation for minor wind direction changes can be 

made by altering the angle of strip fire with the base line. 

Treat major changes in fuel type separately.

An effective method of reducing fire intensity is to use a 

series of spots or short 1- to 2-foot-long strips instead of a 

solid line of fire. An added advantage of these short strips or 

spots is that driptorches will not have to be filled as often. 

Strip-heading fires permit quick ignition and burnout, and 

provide for smoke dispersal under optimum conditions. 

However, higher intensities will occur wherever lines of fire 

burn together, increasing the likelihood of crown scorch.

Occasionally, on areas with light and even fuel distribution, 

a heading fire may be allowed to move over the entire area 

without stripping to better accomplish the objective(s). 

This method reduces the number of areas of increased fire 

intensity that occur each time two fires burn together. 

Caution: Be sure the fire will not escape control. First set 

a backing fire along the downwind control line and allow 

it to burn a strip wide enough to control the heading fire.

factors associated with strip-heading fires: 

• Secure the downwind base line before igniting a 

heading fire. 

• Cost is lower than other line-firing techniques because fire 

progress is rapid and few plow lines are required. 

• Needs just enough wind to give direction (1 to 2 miles per 

hour in-stand). 

• Do not use in heavy roughs. Consider backing or flanking 

techniques if fire-free interval exceeds 3 years or if 

understory vegetation is taller than 3 to 4 feet.

• The technique can accommodate wind shifts up to about 

45 degrees. 

• Winter use is best because cool weather (below 60 °F) 

helps avoid crown scorch. 

• Flame lengths can be high whenever heading fire 

converges with a backing fire, thereby increasing the 

possibility of crown scorch. 

• Can be used in a wide range of forest types depending on 

management objectives.

• A single torch person can progressively ignite strips. 

• Do not force a burn on a marginal day at the low end of the 

prescription window. The fire may burn slowly until after 

the crew leaves, then pick up intensity and escape. 

• Can be used in “flat” fuels such as hardwood leaves. 

• Because fire movement is fast, large blocks can be burned. 

• Can be used with high relative humidity (50 to 60 percent) 

and high actual fine-fuel moisture (20 to 25 percent). 

37

This method of firing can stand little variation in wind 

direction and requires expert crew coordination and 

timing. For safety, all lines of flank fire should be ignited 

simultaneously and all torch people should keep abreast of 

one another.

If only one or two torch people are available, this technique 

is usually altered to set the ignition lines 45 degrees into 

the wind.

In hilly or mountainous terrain, any ignition line that drops 

perpendicularly off a ridge creates a flanking fire under nowind conditions. If several lines are ignited off the end of a 

ridge or knoll, the pattern looks like a chevron or maple leaf.

factors associated with flanking fires:

• Always secure downwind base line first. 

• Fuel loading should be light to medium-less than 8 tons 

per acre. 
38

• Wind direction must be steady. 

• Best used in medium-to-large sawtimber or if crown 

scorch is not a concern (e.g. hardwoods in winter). 

• Allows fast area ignition. 

• Needs few control lines. 

• In areas with a high understory, multiple torch people 

are needed and coordination is very important. Use radio 

communications whenever torch people cannot see 

one another. 

• Useful in securing flanks of other fire types. 

POINT SOURCE FIRES

A prudent burning boss will often switch from strip-heading 

fires to point source fires as the day progresses, relative 

humidity drops, and continuous lines of fire become too 

intense. When properly executed, a grid of spot ignitions 

will produce a fire with intensity much greater than that 

of a line-backing fire but somewhat less than that of a 

line-heading fire. Timing and spacing of the individual 

ignition spots are the keys to the successful application 

of this method. First a line backing fire is ignited across 

the downwind side of the block and allowed to back 10 

to 20 feet into the block to increase the effective width 

of successive ignition lines thus takes place along a moving 

point rather than along a whole line at the same time. 

Merger along a moving point can be ensured by beginning 

with a closely spaced square grid (2 chains by 2 chains is 

recommended).

Close spacing between lines helps the individual spots 

develop, but ensures that the head of one spot will burn 

into the rear of the downwind spot before the heading fire’s 

potential flame length and intensity are reached. With close 

spacing there will be more merging points; but a large 

number of small fires burning simultaneously can produce 

the same kind of explosive convective energy as a single 

large fire because too much heat energy is released too 

rapidly. This situation is discussed under the Aerial 

Ignition section.

Rectangular grids with wider spacing between lines than 

within a line should not be used initially because such a 

pattern may allow the spots along a line to merge into a line 

of heading fire before running into the rear of the downwind 

spots. Once the first few lines have been ignited and fire 

behavior has been assessed, intensity can be regulated to 

some extent by changing the time between ignition points 

within a line, the distance between points, and the distance 

between lines. Thus the balancing act between spacing and 

timing has to be continually adjusted as fire behavior reacts 

to both temporal and spatial changes in fuel and weather.

Intensity is decreased by widening the interval between 

ignition points along a line. If fireline intensity is still too 

high after doubling this interval while maintaining a 2-chain 

Grid, or point source ignition technique.

of the control line. A line of spots is then ignited at some 

specified distance upwind of the backing fire and the process 

continued until the whole block has been ignited.

To reduce flame length, ignition-grid spacing is selected to 

allow the spots along a line to head into the rear of the spots

along the downwind line before the flanks of the individual 

spots merge to form a continuous flame front. The merger 

Point source ignitions.
column ahead of the fire. The indraft, which tends to slow 

heading fires, does not occur on slopes. Fires traveling down 

slopes resemble those backing into the wind. Flame tips are 

tilted away from unburned fuel, so drying is not as rapid and 

fire intensity remains low.

Wind patterns on sloping terrain must also be considered. 

As the earth’s surface warms during daylight hours, air rises 

causing a prevailing upslope wind. Wind speed increases 

with elevation because greater volumes are moving upslope. 

The combination of upslope effects and upslope winds will 

cause heading fires to travel much more quickly than on flat 

terrain. Prevailing upslope winds are most common under 

clear skies and weak pressure gradients. Strong pressure 

systems create heavy winds that may completely offset 

convection effects. In rugged terrain, particularly in the 

steep southern Appalachian Mountains, deep cuts between 

toe slopes, known as draws, can impact fire behavior. 

Upslope winds are funneled into these draws, creating the 

effect of a chimney. Fires set at the bottom of a draw can 

be especially fast moving because of the combination of a 

heading fire, upslope wind, and the chimney effect.

Fuel moisture content varies by aspect in sloping terrain. 

Ridges and slopes with a southern exposure receive more 

radiation than those with a northern aspect. Therefore, fuel 

drying is much slower on north-facing slopes and prescribed 

burning is more difficult. In many cases, a backing fire can 

readily be used on the southern side of a mountain whose 

northern side cannot support even a heading fire because 

fuel moisture content is too high. 

39

distance between lines, firing should be halted. Allow the 

area to burn with a backing fire or plow it out. Although 

intensity at the head of an individual spot is increased by 

widening the distance between lines, the average intensity 

of the burn as a whole is usually somewhat lower. Check to 

see that convergence-zone flame lengths are within tolerable 

limits and that other fire behavior parameters appear 

satisfactory. If everything is within prescription, you can 

increase both between- and within-line distances. This step 

will reduce ignition time and decrease the number of people 

on the ignition crew. The number of convergence areas with 

their higher intensities will also be decreased.

Experience to date shows grids up to 4 chains by 4 chains 

(one ignition point every 1.6 acres) can produce excellent 

results. The time needed to complete the burn can be 

reduced by offsetting successive ignition lines by one half of 

the within-line spacing. The heading fires from one line will 

then come up between the backing fires on the next line.

factors associated with Point source fires:

• Assume much of the area will be burned by heading and 

flanking fires and very little by backing fires. 

• If conditions are ideal for traditional line-backing fires, 

point source fires may be too intense. 

• Preferred burning conditions include low (1-2 miles per 

hour) in-stand wind speeds. Wind direction can be variable. 

Actual fine-fuel moisture should be above 15 percent. 

• When underburning, start with a square ignition grid 

(equal distance between spots within a line and between 

lines). Two chains by 2 chains is often used. 

• Always secure the downwind base line first. 

• Be careful when underburning stands with a flammable 

understory or a heavy rough. 

• Severe crown scorch is likely if fuel is too dry. 

• The usual changes in weather during a typical winter day 

may require modification of ignition patterns throughout the 

day. Burn until fires verge on getting “too hot.” Then either 

quit burning or resort to backing fires only. 

• Continually modify the ignition grid to take advantage of 

topography and changes in understory fuels. 

• Costs are low because firing is rapid and no interior control 

lines need to be constructed. 

PRESCRIBED BURNING ON SlOPES

Sloping terrain, which is common throughout the Piedmont 

and Mountain regions of the South, can complicate 

prescribed burning. Effects of slope on fire are similar in 

some way to those of wind. A fire traveling up a steep slope 

resembles one being pushed by a steady wind. The hot tip 

of the flame is tilted toward unburned fuels promoting fuel 

drying and increasing fire intensity. However, fires burning 

on level terrain produce an indraft caused by a convection Fires burning up a slope behave like a heading fire.
40

Differences in species composition between north- and 

south-facing slopes can also impact fire behavior. At 

elevations less than 4,000 feet, south-facing slopes and 

ridges may have a higher component of pines and ericaceous 

shrubs than north-facing slopes which are dominated by 

hardwoods. Pine needles and leaves of ericaceous shrubs 

ignite more easily than do the leaves of hardwoods. Also, 

shrubs can act as a vertical fuel creating intense fires when 

they are dense.

AERIAl IGNITION

When ground ignition techniques are used, the downwind 

spots will usually coalesce and burn out before the whole 

block has been ignited. In contrast, aerial firing permits 

ignition of a block to be completed before the downwind 

spots have burned out. This does not present a problem 

at the damp end of the prescribed burning window when 

actual fine-fuel moisture is near 20 percent. Rapid ignition 

of a block reduces both flying time and the time needed to 

complete the burn. However, when using aerial ignition 

techniques under “traditional” ideal burning conditions for 

line-backing fires, rapid ignition of the entire area can result

in fire intensity increasing to unacceptable levels. In this 

situation, there is little recourse except to let the area 

burn out.

Some experienced burners start firing early in the day, 

before the fuel is dry enough to carry fire well. They reduce 

the distance between spots within a line to less than 2 chains 

by 2 chains. The increased number of ignitions creates 

more heat and helps dry the surface fuels. The distance 

between spots must be expanded as the morning progresses 

and burning conditions improve. Otherwise, the spots will 

merge laterally forming lines of heading fire that get too 

intense before reaching the next downwind line of ignition 

points. The distance between lines can also be increased as 

necessary to maintain a square ignition grid.

The most common aerial ignition device used today is the 

DAID (Delayed Aerial Ignition Device) or ping-pong ball 

system. Small plastic spheres, similar in size and appearance 

to ping-pong balls, contain potassium permanganate and 

are injected with ethylene glycol by the DAIDS machine. 

Spheres are jettisoned before the chemicals react thermally 

to produce a flame that consumes the ball. The dispensing 

machine can be mounted in small airplanes or helicopters. 

The ping-pong ball system works best in continuous fuels or 

in areas where a mosaic burn pattern is desired.

Aerial ignition dramatically reduces the time needed for 

an area to burn out. Although roughly the same amount of 

smoke is produced, it is emitted over a shorter period and 

more of it is entrained in the convection column. Thus, the 

impact of any adverse air quality effects is much reduced.

factors associated with aerial Ignition: 

• Rapid firing and burnout allows use of a much smaller 

prescription window. 

• Damp, fine fuels are of critical importance. Actual fine-fuel 

moistures of 15 to 25 percent are preferable. 

• Requires an experienced burn boss to make ignition grid 

adjustments and to determine when to halt ignition due 

to conditions. 

• Although not likely under prescribed fire conditions, too 

much heat energy released over too short a period will result 

in a sudden, dangerous increase in fire intensity. 

• Large acreages can be safely burned in a single 

burning period. 

• Many widely dispersed tracts can be burned during a 

single day. 

• A contingency plan is essential in the event the aircraft is 

reassigned or equipment breaks down during operation. 

• Best suited for continuous fuels or when a mosaic pattern 

is desired. 

• Ignition spacing within and between flight lines can be 

easily adjusted. 

• Make sure no DAIDs are mistakenly dropped outside the 

burn as the helicopter turns at the end of each line.

Delayed Aerial Ignition Device (DAID) mounted in a 

helicopter, Bugwood.org.
CENTER AND CIRCUlAR (RING) FIRING

This technique is useful on cutover areas where a hot fire 

is needed to reduce or eliminate logging debris prior to 

seeding or planting. It works best when winds, if any, are 

light and variable. This procedure should never be used for 

underburning because of the likelihood of severe fire effects 

as the flame fronts merge.

As with other burning techniques, the downwind control 

line is the first line to be ignited. Once the base line is 

secured, the entire perimeter of the area is ignited and the 

flame fronts are allowed to converge. One or more spot fires 

are often ignited near the center of the area and allowed to 

develop before the perimeter of the block is ignited. The 

convection generated by these interior fires creates indrafts 

that help pull the outer circle of fire toward the center. This 

firing method can generally be used in any season, and 

weather conditions are not as critical. However, caution is 

in order, particularly when the atmosphere is unstable. This 

type of fire tends to develop a strong convection column 

which can cause spotting a considerable distance downwind.

PIlE AND WINDROW BURNING

The objective of piling logging debris before burning it is 

to prolong fire residence time on a restricted area so that 

larger materials have time to be consumed. Some areas will 

contain an unacceptable amount of large, scattered debris 

that must be concentrated to ensure consumption. This 

material should be piled and not windrowed. Windrowing 

can reduce site quality by removing topsoil. Full exposure of 

the soil to the sun and rain bakes the top layer. Furthermore, 

the direct force of raindrops will clog soil pores and often 

results in erosion on steep slopes. The area beneath the 

41

Center firing technique.

Piles burn more efficiently than windrows.

windrows is lost to production because the debris is rarely 

consumed completely and what remains makes planting 

difficult or impossible. Even when windrows contain breaks 

spaced every couple of chains, they still present a barrier to 

firefighting equipment and wildlife.

The biggest deterrent to windrow burning, however, is that 

it causes a high percentage of all smoke incidents. Large 

volumes of fuel, including large pieces that contain a lot 

of moisture, are consumed. However, oxygen for good 

combustion is lacking, especially in large piles and wide 

windrows. Large amounts of soil are often mixed in, further 

compounding the problem. The result is a fire that continues 

to smolder for days or weeks, creating air quality problems 

because the smoke produced by smoldering combustion 

is not hot enough to rise into the atmosphere. The smoke 

stays near the ground where it cools even more, drifting and 

concentrating in low areas because of cool air drainage. To 

make matters worse, the smoke often mixes with humid air 

to produce fog which further reduces visibility. For these 

reasons, air quality regulations prohibit pile and windrow 

burning in some areas.

Although it generally costs more to pile than to windrow, 

piles are preferable to windrows because access within the 

area is not a problem, planting is easier, burning is safer and, 

most important, smoke problems are significantly reduced 

since piles burn out much quicker.

Generally, piles contain less dirt and dry faster. Burning 

piles can be “bumped” with heavy equipment to remove any 

dirt and compressed to increase consumption. 
42

Keep piles small and minimize the amount of soil in them 

so surface water can pass through, and the debris can dry 

quickly. Always pile when the ground surface is dry; less 

soil compaction will take place, and considerably less soil 

will end up in the piles. Allow fresh logging debris to cure 

first and to dry after rain. Then “shake” the debris while 

piling to remove as much soil as possible. If material is 

piled while green or wet, the centers of the piles take an 

exceedingly long time to dry. Piles that contain little soil 

and are constructed to allow some air movement will result 

in a burn that consumes significantly more of the debris 

and produces less smoke. More efficient burning and 

greater heat output will lift smoke higher, reducing smoke 

concentrations near the ground. Burn when the atmosphere 

is neutral to slightly unstable, but not unstable enough to 

create control problems.

Techniques used in burning piled debris are somewhat 

fixed because of the character and placement of fuel. 

Traditionally, each pile is ignited along its perimeter, but 

burnout can be speeded up considerably by igniting the pile 

center by tossing one or more fusees into the pile. 

factors associated with Pile and Windrow burning:

• A large majority of all smoke-related incidents are caused 

by this type of burning. 

• Produces the most smoke of all firing techniques. 

• Burns can continue to smolder for many weeks. 

• Smoke produced at night tends to stay near the ground. 

• Cannot be readily extinguished after ignition. If 

extinguished, even more effort is required to reignite them 

the next day. 

• Can burn in light or variable winds. 

• Usually safe and easy to control, provided piles are not 

next to the edge of the area and are not left unattended, 

particularly when burning during periods of high fire danger. 

• Piles should be as free of soil as possible. 

• Fuel should be dry. 

• Burn area should be as small as economically practical. 

• Need neutral to unstable conditions for good smoke 

dispersion -which generally do not occur after sunset. 

• Need good mixing heights and transport winds.

• Use of heavy equipment to bump piles expedites burning.
Smoke Management

INTRODUCTION

Prescribed burning helps achieve many desired resource 

benefits, but it nevertheless pollutes the air. We therefore 

have an obligation to minimize adverse environmental 

effects. If this obligation is disregarded, prescribed burners 

can be held liable for damages from accidents or other 

problems resulting from their actions.

Smoke management can be broken down into three primary 

tasks: knowing how much smoke will be produced, knowing 

where the smoke will go, and understanding the potential 

impacts the smoke will have. The amount of smoke 

produced is directly related to the amount and moisture 

content of the fuel that is to be burned, fireline intensity and 

combustion rate. Where the smoke will go is controlled by 

the prevailing weather, particularly the transport winds and 

mixing height during the day. At night, topography becomes 

an important factor as smoke tends to drift and collect in 

drainages. The impact smoke will have is dependent upon 

the smoke concentration and who/what is impacted.

Mitigating the adverse impacts of smoke is the key to 

effective smoke management. Impacts range from simple 

nuisance levels and regional haze to more severe health 

impacts and visibility reductions that pose a threat to 

Table 1: Listing of Class I Areas in the South 

State Class I Area Acres 

Alabama Sipsey Wilderness Area 24,922 

Arkansas Caney Creek Wilderness Area 14,460 

Upper Buffalo Wilderness Area 12,035 

Florida Everglades National Park 1,506,499 

Chassahowitzka National Wildlife Refuge 23,580 

St Marks National Wildlife Refuge 17,350 

Bradwell Bay Wilderness Area 24,602 

Georgia Cohutta Wilderness Area 36,977 

Okefenokee National Wildlife Refuge 353,981 

Wolf Island National Wildlife Refuge 5,126 

Kentucky Mammoth Cave National Park 52,707 

Louisiana Breton National Wildlife Refuge 5,000 

North Carolina Linville Gorge Wilderness Area 12,002 

Shining Rock Wilderness Area 16,133 

Swanquarter National Wildlife Refuge 8,785 

South Carolina Cape Romain National Wildlife Refuge 29,000 

Tennessee/North 

Carolina 

Great Smoky Mountains National Park 520,269 

Joyce Kilmer – Slickrock Wilderness Area 17,394 

Texas Big Bend National Park 801,163 

Guadalupe Mountains National Park 46,850 

Virginia Shenandoah National Park 79,579 

James River Face Wilderness Area 8,903 

public safety. A State’s Smoke Management Program 

(SMP) is designed to help limit potential smoke problems 

by establishing a basic framework of procedures and 

requirements for managing prescribed fires with the goal 

of successfully balancing the use of prescribed fire with the 

constraint of maintaining clean air. Consult with your local 

forestry agency to learn more about your State’s SMP.

SMOkE MANAGEMENT PlANNING

This section describes the development of a rather extensive 

but flexible smoke management planning process. The 

planning process is divided into two components: a daytime 

smoke evaluation and a nighttime smoke evaluation. This 

process is designed to fulfill the following objectives:

• Minimize exposure of populated areas to smoke.

• Minimize public health and safety hazards (impacts to 

sensitive sites such as schools, hospitals and nursing homes 

and visual impairment of roadways and airports). 

• Avoid violations of National Ambient Air Quality 

Standards (NAAQS).

• Protect visibility of Class I areas (Table 1).

• Make certain that you fully comply with your State’s 

mandatory or voluntary Smoke Management 

Program (SMP).

43
44

DAYTIME SMOkE EvAlUATION

Estimating the potential smoke impacts from a fire can 

be complicated. This process is designed such that the 

complexity of the smoke management process should not 

exceed the scale/complexity of the prescribed fire. Elements 

that increase the complexity of a prescribed burn (from a 

smoke management standpoint) are:

SIzE–not just total acres, but also the number of acres in 

the active fire phase at any given time.

DURATION—the longer the duration, the more likely 

weather conditions are to change during the burn. Primary 

focus is the duration of the flaming phase of combustion.

FUEl lOAD—the more fuel consumed in the flaming 

phase, the more heat released during that phase, and the 

stronger the convective column. While a well-developed 

convective column is good for smoke management as it 

gets the smoke up and away from the surface; it typically 

requires more planning as winds above the mixed layer can 

be quite different from surface or transport winds.

The amount of smoke produced by a fire depends upon the 

amount of fuel consumed which in turn depends on the 

amount of available fuel and its moisture content. A number 

of tools are available to assist in estimating the fuel load on 

Table 2: Fire Behavior Fuel Models, Fuel Load and Consumption Estimates. 

Estimated Fuel Consumption 

(tons per acre) 

Number Description Fuel Load 

(tons per 

acre) Moist Moderate Dry 

Grass dominated 

1 Short grass (<= 1 ft) 0.74 0.5 0.6 0.7 

2 Timber with grass 

understory 

4.00 1.8 2.6 3.2 

3 Tall grass (>2.5 ft) 3.00 2.0 2.3 2.4 

Chaparral and shrubs 

4 Chaparral 16.00 10.0 12.1 13.0 

5 Brush 3.50 2.2 2.6 2.9 

6 Dormant brush 6.00 3.8 4.5 5.0 

7 Southern rough 4.87 2.6 3.4 4.0 

Timber litter 

8 Closed timber litter 5.00 2.6 3.0 3.3 

9 Timber litter 3.48 2.0 2.4 2.7 

10 Timber (litter and 

understory) 

12.00 5.2 6.5 7.1 

Slash 

11 Light logging slash 11.50 8.0 9.7 10.5 

12 Medium logging slash 34.00 23.6 28.8 31.0 

13 Heavy logging slash 58.00 40.0 49.0 52.8 

Consumption estimates calculated using FEPS v 1.1.0 and default fuel moisture scenarios as 

named above. These numbers are provided as a rough estimate and may not match a particular 

site or fuel moisture conditions.

Consumption estimates calculated using FEPS v 1.1.0 and default fuel moisture scenarios as named above. These numbers are provided as a 

rough estimate and may not match a particular site or fuel moisture conditions.

a site (often expressed in tons of fuel per acre). The basic 

fire behavior fuel models (Anderson, 1982; http://www.

fs.fed.us/rm/pubs/rmrs_gtr153.pdf) can provide a rough 

estimate. In many cases digital maps are available that show 

the spatial distribution of the fire behavior fuel models or 

other fuel modeling tools such as the fuels characteristics 

classification system (FCCS; http://www.fs.fed.us/pnw/fera/

fccs). Digital photo series are also available for a variety of

ecosystems that allow for fairly rapid characterization of the 

fuels at a site (http://www.fs.fed.us/pnw/fera/research/fuels/

photo_series). Multiplying a fuel load estimate by the area 

of the burn provides an estimate of the total fuel available.

The amount of fuel consumed by the fire will depend on the 

moisture content of the fuels. Moisture in the fuels acts as 

a heat sink to the fire as energy must be expended to drive 

the moisture out of the fuels, leaving less energy available 

for combustion. Fuel moisture content can be estimated 

as described in the weather chapter. A rough estimate of 

fuel consumption is provided in Table 2 and more detailed 

estimates can be obtained from a number of computer 

programs (e.g., CONSUME, FOFEM, or FEPS). A good 

rule of thumb is to assume most prescribed underburns 

conducted under the range of acceptable conditions used 

in this guide will consume less than 5 tons of fuel per acre. 

Fuel consumption in a number of grass dominated systems 

such as tall-grass prairies and salt and fresh water marshes 

can approach 10 tons per acre. Consumption of broadcast 
DAYTIME SMOkE MANAGEMENT COMPlExITY WORkSHEET

The following worksheet is provided as a guide to determining the complexity of a smoke management situation. Knowing 

the complexity can help determine the appropriate level of smoke screening required for a burn. Note this worksheet is only 

dealing with the daytime, active burning portion of the burn, not residual burning/smoldering or nighttime conditions.

45

Acres in Flaming Combustion Stage per Hour

(1) Size in acres ________acres

(2) Expected duration of flaming combustion stage for burn _______hours

(3) Divide (1) by (2) ______ acres/hour

(4) Select values based on (3)

 < 150 acres/hr = 0

 150-300 acres/hr = 1

 > 300 acres/hr = 2 Score _______________ 

Fuel Load Consumed

 < 4 tons per acre = 0

 4-8 tons per acre = 1

 > 8 tons per acre = 2 Score _______________

Topography

Flat terrain with no significant topography within 30 miles downwind of the burn unit = 0

Flat terrain with significant topography within 30 miles downwind of the burn unit = 1

Burn unit is in significant topography = 2 Score _______________ 

Ambient Air Quality (based on AQI from http://www.airnow.gov)

 Good = 0

 Moderate = 2

 Other = Do not burn Score _______________ 

Atmospheric Dispersion (as determined from tables in weather section)

 Good dispersion = 0

 Acceptable dispersion = 1

 Poor dispersion = DO NOT BURN Score _______________ 

WuI

 No urban areas with in 60 miles downwind of burn site = 0

 Burn unit not in an urban area, but urban areas are within 60 mile downwind = 1

 Burn unit is in a WUI area = See Wade and Mobley (2007)

 Score _______________ 

 Total _______________

Scores 

0-2 (with no individual elements receiving a score of 2) = Low complexity smoke situation

3-6 (with no more than two elements receiving a score of 2) = Moderate complexity smoke situation

7+ = High complexity smoke situation

Low complexity burns – simple smoke screening
46

Table 3: Downwind Screening Distance

 Consumption (tons per acre) Distance (miles)

< 0.5 0.25

0.5-1.0 0.50

1.0-2.0 4.00

2.0-3.0 12.00

3.0-4.0 25.00

4.0-6.0 60.00

6.0-8.0 100.00

lOW COMPlExITY BURNS—use simple smoke 

screening.

Step 1: Determine the screening distance based on the 

expected fuel consumption (table 3).

Step 2: Using a map on which smoke sensitive areas can be 

identified, locate the burn unit and mark its center.

Step 3: Draw a line through the center point along the 

preferred wind direction for this burn that extends out the 

distance calculated in Step 1 (fig. A).

Step 4: Draw a line through the center point perpendicular 

to the line drawn in Step 3 that extends the width of the burn 

unit (fig. B). At each end of this line, draw lines parallel to 

the line drawn in Step 3. This is your anticipated 

smoke path.

burned heavy debris generally ranges between 6 and 8 tons 

per acre although when jackstrawed and deep (can’t walk 

on ground), consumption can exceed 20 tons per acre. If 

debris is piled in roughly circular piles less than about 15 

feet in diameter when cured and dry, burned when dry, and 

“bumped” during burning expect more than 85 percent to 

be consumed.

TOPOGRAPHY—topography adds to the complexity of 

daytime burns by altering wind patterns and channeling 

smoke under stable conditions. At night down drainage 

flow tends to dominate most of the time and will control the 

movement of smoke at night.

BACkGROUND AIR qUAlITY—the ambient 

atmosphere always has some level of particulate matter. 

The Air Quality Index (AQI) provided by the EPA through 

http://www.airnow.gov provides guidance on how air quality 

may impact human health and considers impacts from both 

particulate matter and ozone. 

ATMOSPHERIC DISPERSION—the atmosphere’s 

ability to disperse pollutants changes with the weather as 

this ability is a function of the mixing height, transport 

wind, and atmospheric stability. Dispersion is normally 

characterized by an index such as the Ventilation Index (VI) 

or Atmospheric Dispersion Index (ADI). See the chapter on 

weather for tables of acceptable values of these indices.

WIlDlAND URBAN INTERFACE—close proximity to 

urban areas is a complicating factor as it provides less time 

for the atmosphere to disperse smoke to levels low enough 

to prevent adverse impacts. Urban areas downwind of burn 

units can also present a complicating factor as the mixed 

layer can often be deeper over the urban area due to the 

urban heat island effect. This deeper mixed layer can take 

smoke that was injected above the mixed layer and mix it 

back down to the surface over the populated area. 

Figure A

Figure B
Examples of Mitigation Techniques

Contact people known to be sensitive to air pollution prior to the ignition of the prescribed fire if they 

could be impacted by smoke. This could include hospitals, nursing homes, isolated residences, etc. 

News releases in newspapers and by radio or TV may be appropriate. Notification to local law enforcement and government agencies prior to burning can save much time in answering citizen concerns.

Temporarily relocate affected people by providing hotel rooms for the day/night of the burn. Encourage 

people to close all windows and doors during the day and night of the burn to reduce their exposure to 

smoke.

Notify public safety agencies such as State Highway Patrol, County Sheriff, Local Law Enforcement, 

Highway Departments. State Forestry and Air Quality offices should also be included.

Post smoke-warning signs to warn the public of areas where smoke may create a hazard to driving. 

Patrol potentially affected areas (especially at night and during early morning hours) to ensure residual 

smoke is not causing safety concerns. Be prepared to move smoke signs as needed.

Temporarily closing roads to traffic until smoke clears. Obtain assistance of appropriate jurisdictional 

authorities (Department of Transportation (DOT), Sheriff, State Highway Patrol) when traffic control is 

necessary to reduce the risk of accident from smoke on public roads.

If you anticipate a road visibility problem ask for assistance of appropriate jurisdictional authorities 

(Department of Transportation (DOT), Sheriff, State Highway Patrol) several days before planned 

burn day. Consider public service announcement asking people to use alternative route for a given time 

period. For sudden unexpected serious reductions in road visibility, call 911 and stop traffic until smoke 

clears. You don’t want any traffic accidents on your conscience

Clearly document any measures to be taken in dealing with 

smoke sensitive targets and note who is responsible for each 

mitigation measure.

If results from the simple smoke screening appear too 

restrictive, try the more detailed planning approach 

recommended for moderate complexity burns.

To allow for horizontal dispersion of the smoke as well as 

wind shifts draw two lines at 30 degree angles from the 

anticipated smoke path. The result is the probable daytime 

smoke impact area. Note that you will need to repeat this 

process if the wind direction is expected to change during 

the burn. On many maps, one can manipulate placement 

of the center line intersection because of map scale or unit 

shape—be conservative and err on “do not burn” side.

Locate all smoke sensitive targets within or immediately 

adjacent to the area of potential smoke impacts. Smoke 

sensitive targets include, but are not limited to areas of 

existing air pollution/visibility problems, non-attainment 

areas, airports, communities, schools, highways, hospitals/

nursing homes, Class I areas, and metropolitan areas.

Determine what adjustments to the prescription or 

mitigation steps are necessary to achieve the smoke 

management objectives.

47

MODERATE COMPlExITY BURNS—By definition 

moderate complexity burns are more likely to cause 

smoke problems than those of low complexity, and they 

therefore require a greater level of precision in assessing 

their potential impacts. The Southern Forestry Smoke 

Management Guidebook (see Mobley and others, 1976 

in Suggested Reading) presents a system for estimating 

particulate matter concentrations at various distances 

downwind of a burn. VSMOKE is a computer program 

that provides an alternative means of estimating smoke 

concentrations from a burn (Georgia Forestry Commission 

has implemented a web-based version of VSMOKE, http://

vsmoke.gfc.state.ga.us/Vsmoke/index.aspx, as has the 

Southern High Resolution Modeling Consortium, SHRMC, 

http://shrmc.ggy.uga.edu/maps/vsmoke.html).

As with the simple smoke screening for the low complexity 

burns, VSMOKE assumes a constant wind direction 

throughout the burn. If weather conditions are expected to 

be changing throughout the course of the burn (sea breeze 

or approaching frontal system as examples) then a more 

complex smoke dispersion model such as HYSPLIT or 

BlueSky should be used as both of these models utilize 

detailed, time varying weather information to predict smoke 

movement in three dimensions.
The HYSPLIT (HYbrid Single-Particle Lagrangian 

Integrated Trajectory) model developed by NOAA is a 

complete system for computing simple air parcel trajectories 

and conducting complex dispersion simulations. The model 

can be run either interactively on the Web through the 

READY system or run on a Windows PC. HYSPLIT can be 

48

Hysplit trajectories showing possible plume paths over a 12 hour period.

accessed online at http://www.arl.noaa.gov/ready/hysplit4.

html. HYSPLIT provides a pair of useful tools for smoke 

management: trajectories and concentration predictions. 

Trajectories show the path that the smoke will follow 

through time and can be useful in cases where the winds 

are expected to shift somewhat during the day. While these 
Sample output from Bluesky showing surface PM 2.5 concentrations.

HIGH COMPlExITY BURNS—Smoke modeling for 

this class of burn is no different than for the moderate 

complexity burns presented above; the real difference comes 

in the level of coordination/communication required with 

local air quality and forestry agencies as well as the public. 

At this level of complexity adverse smoke impacts are 

probable and the goal for smoke management becomes one 

of trying to maintain the impact as no more than a nuisance 

while preventing the impact from threatening public health 

and safety. Review the prescription and determine which 

aspects of the prescription can possibly be altered to offer 

improvements for smoke management such as changing the 

amount and/or rate of fuel consumption, better ventilation 

values, or use of a firing technique more likely to loft smoke 

above the mixed layer such as aerial ignition.

BURNING AT THE WIlDlAND URBAN 

INTERFACE—Few WUI prescribed fire projects can 

pass any of the smoke screening systems currently in 

49

paths do not provide information on how much smoke will 

reach a location, they do help in determining the potential 

smoke impact area. The surface concentration output 

from HYSPLIT provides information on expected smoke 

concentrations every hour which can help to further refine 

estimates of potential smoke impact.

BlueSky is not a smoke model, but rather a modeling 

framework that integrates a number of the tools mentioned 

previously in this chapter to predict cumulative impacts 

of smoke from forest, agricultural, and range fires across 

the landscape. BlueSky includes tools for estimating 

fuel loading, fuel consumption, emissions calculation, 

trajectories (using HYSPLIT) and dispersion using a model 

known as CalPUFF. Utilizing predictions from a weather 

forecast model and fire information, BlueSky creates 

forecasts of ground concentrations of smoke. See http://

www.getbluesky.org and http://www.fcamms.org for

more information.
50

smoke dispersion conditions typically begin to develop 

around one hour before sunset and continue until one hour 

after sunrise. These conditions are normally characterized 

by a surface temperature inversion which acts as a lid to 

limit the vertical dispersion of the smoke. The primary nonfire factors that need to be evaluated for nocturnal smoke 

dispersion are topography, winds and relative humidity.

Winds at night are often weaker than during the day. The 

inversion which acts to trap smoke near the ground also 

acts to decouple the surface winds from larger scale wind 

patterns which allows local features such as topography to 

play a greater role in shaping smoke dispersion conditions. 

As the air cools, it tends to flow down drainages. The 

steeper the slope of the drainage, the faster these winds 

will be. The cold air will pool in valleys at the base of the 

drainage. Smoke will also follow this pattern, most of 

the time.

As the wind speed at night gets stronger, the role of 

topography decreases. This can cause smoke at night to 

instead move upslope/upvalley. Key factors to look at for 

assessing the potential for wind to alter the anticipated down 

drainage flow are orientation of the wind direction to the 

topography and the depth of the drainages/valleys. The more 

the wind direction parallels the axis of the drainage/valley, 

the greater its potential influence on smoke dispersion. 

Deeper drainages tend to be more resistant to influence from 

larger scale winds.

Table of LVORI values as a function of Atmospheric Dispersion Index and Relative Humidity. Green = Conditions with lowest 

proportion of accidents. White = proportion of accidents increased by a factor of 2-10 over green. Yellow = proportion of accidents 

increased by a factor of 10-40 over green. Orange = proportion of accidents increased by a factor of 40-150 over green. 

use, but prescribed burning is none-the-less necessary to 

perpetuate fire-dependent plant communities in the WUI 

and help reduce hazardous fuel accumulations. For these 

reasons, the Southern Smoke Screening System originally 

described in the Southern Forestry Smoke Management 

Guidebook has been modified to facilitate successful smoke 

management when burning is conducted at the WUI. The 

resulting system, the WUI Smoke Screening System, is 

largely based on extensive fieldwork conducted by Hugh 

Mobley, which he used to modify the original version of the 

Southern Forestry Smoke Management Guide. (To see the 

guide as modified by Mobley, go to https://fp.auburn.edu/

fire/, click on “Fire Management,” then click on “Smoke 

Management.”) Wade and Mobley (2007) further modified 

the Southern Forestry Smoke Management Guide screening 

system for application in the WUI as part of a training 

course developed by the Florida Division of Forestry; 

the resulting WUI Smoke Screening System is a five step 

system intended specifically for WUI burns smaller than 50 

acres and is available online at http://www.treesearch.fs.fed.

us/pubs/28550.

NIGHTTIME SMOkE EvAlUATION

Evaluation of nighttime smoke dispersion conditions is 

important for any burn that is still expected to have flaming 

combustion one hour before sunset or when significant 

smoldering is expected to continue into the night. Nighttime 

Atmospheric Dispersion Index (ADI)

RH 1 2 3-4 5-6 7-8 9-10 11-12 13-16 17-25 26-30 31-40 > 40

< 55 2 2 2 2 2 2 2 2 2 2 1 1 

55-59 3 3 3 3 3 2 2 2 2 2 1 1 

60-64 3 3 3 3 3 3 2 2 2 2 1 1 

65-69 4 3 3 3 3 3 3 3 3 3 3 1 

70-74 4 3 3 3 3 3 3 3 3 3 3 3 

75-79 4 4 4 4 4 4 4 4 3 3 3 3 

80-82 6 5 5 4 4 4 4 4 3 3 3 3 

83-85 6 5 5 5 4 4 4 4 4 4 4 4 

86-88 6 6 6 5 5 5 5 4 4 4 4 4 

89-91 7 7 6 6 5 5 5 5 4 4 4 4 

92-94 8 7 6 6 6 6 5 5 5 4 4 4 

95-97 9 8 8 7 6 6 6 5 5 4 4 4 

> 97 10 10 9 9 8 8 7 5 5 4 4 4 
Residual smoke from a daytime burn and smoke released 

during a nighttime burn typically flows down drainages 

and through gaps (such as power lines, streams and roads). 

However, smoke will also tend to pool in open areas such 

as pastures and if smoke is being produced faster than it is 

flowing down slope, then the smoke may find other means 

of escaping the area and may even move up drainage. If 

down drainage smoke encounters dense vegetation, as it 

well might in a swamp or bottomland forest, it will dam up 

and spread across open areas even if uphill. The following is 

a basic screening process for nighttime smoke management. 

Keep in mind that a screening process is designed to give 

you an idea of where the smoke is likely to go. It is not a 

substitute for monitoring where your smoke is 

actually going.

51

Relative humidity is a complicating factor for smoke 

management at night. Conditions that favor poor smoke 

dispersion, light winds and a strong temperature inversion, 

also favor the formation of fog when the relative humidity 

nears 100 percent. Since the primary smoke concern at 

night is visibility reduction, the added possibility of another

factor capable of reducing visibility increases the potential 

threat to public safety. Further complicating the situation is 

the fact that combustion releases additional moisture in the 

air which can raise the relative humidity evens further, in 

rare instances resulting in supersaturation (relative humidity 

values that exceed 100 percent!).

The Low Visibility Occurrence Risk Index (LVORI) is 

designed to provide burners with an indicator for the 

potential for visibility related accidents to occur under a 

certain set of meteorological conditions (relative humidity 

and atmospheric dispersion index). The LVORI was 

develop by examining vehicle accident reports from the 

Florida Highway Patrol and examining the portion of these 

accidents that cited fog, smoke or both as a contributing 

factor along with the meteorological conditions. This is 

a conservative estimator because one can smell minute 

concentrations of smoke, long before it can be seen. The 

LVORI estimates the likelihood of smoke or fog being a 

contributing factor in an accident and is expressed on a 

scale of 1-10 (with 10 representing the highest likelihood of 

smoke/fog contributing to an accident).

The first step is to figure out how far the smoke is likely to 

travel over the course of the night. Use a screening distance 

of 10 miles for the coastal plain, 15 miles for the piedmont, 

or 30 miles for the mountains. If surface wind speed exceeds 

5 miles per hour, extend the radius an additional 5 miles in 

the coastal plain and piedmont and 10 miles in 

the mountains. 

If winds are over 5 miles per hour, the problem is much 

more complicated as the winds can overpower the drainage 

flows which can move smoke up drainage in some cases. 

Examine the relationship between the forecast wind 

direction and the drainages. If the winds are forecast to be 

parallel to the drainage then the winds will either enhance 

or reverse the flow in the drainage. If the wind direction is 

perpendicular to the drainage then the wind might have little 

impact on the drainage flow. Deep, narrow drainages are less 

likely to be impacted by cross flows.

Draw a circle on a topographic map with a radius equal to 

the screening distance.

Determine which drainages pass through or are adjacent 

to the burn unit. Use the topographic map to find nearby 

streams and drainages as well as local knowledge of forest 

gaps such as roads and power lines to identify where smoke 

is likely to move. Do not neglect open areas such as pastures 

in which smoke can pool and possibly connect with other 

drainages. Follow down these drainages out to the screening 

distance.

Identify smoke sensitive features in the marked drainages.

Describe in the prescribed burn plan what will be done to 

mitigate potential smoke impacts (especially for roads).

As an alternative to this screening process, a predictive 

model is available. Planned Burn-Piedmont, or PBPiedmont is a weather/smoke dispersion model specifically 

designed for nocturnal smoke movement. PB-Piedmont 

requires digital elevation data and forecast weather 

information as inputs. Additional information on PBPiedmont is available through the Southern High Resolution 

Modeling Consortium (http://www.shrmc.org).
52

OTHER POINTS TO CONSIDER

When using mass ignition or other techniques that favor the 

development of a vertical convective column, a portion of 

the smoke (30 percent or more typically) is likely to disperse 

ABOVE the mixing height where dispersion is generally 

poor. The wind above the mixing height is often from a 

different direction than the transport wind.

The mixing height is generally deeper over urban areas than 

over the forest. Smoke lofted above the mixing height while 

not impacting rural areas is likely to mix back down to the 

ground over urban areas.

Plumes from multiple prescribed fires can merge and cause 

a much larger air quality impact than one might expect. 

Thus the prudent burner will ask the agency issuing the 

burn permit/authorization if any other units over about 750 

acres in size have received a go-ahead on that day. If the 

answer is yes, one should spend some time ruminating over 

the information including the distance and direction from 

his/her planned burn before deciding whether to proceed or 

postpone the burn. It is often worthwhile to call the other 

burner and discuss the situation as you might be able to 

stagger the timing of the burns if using aerial ignition, or 

one or both of you might be willing to burn less acreage 

that day. 

Avoid igniting organic soils as they are difficult to 

suppress and can smolder for long periods of time, creating 

significant residual smoke problems. A good rule of thumb 

is not to burn such areas when the water table is below 

the surface.

Verify that the smoke is behaving as expected. Document 

smoke behavior with photographs when possible, 

particularly in cases where smoke may impact a road.

If smoke sensitive targets are likely to be adversely 

impacted, explore possible mitigation strategies. Managing 

emissions revolves around manipulating the amount of fuel 

consumed. This can be accomplished by burning a smaller 

area, burning under higher moisture conditions, or applying 

a preburn herbicide or mechanical treatment.

Have a contingency plan if things go wrong. If smoke 

begins reducing visibility on a roadway know who to 

call and be prepared to take whatever steps necessary to 

minimize the threat—road closure, posting signs, traffic 

control, suppressing the fire if needed.

When nighttime residual smoke is expected within a mile 

or so of an urban area or paved road, or when it is obvious 

that there is considerable smoldering after the flame front 

Sample output from PB-Piedmont showing smoke (yellow particles) moving down drainages and crossing roads at points A, 

B, and C. 
passes, begin mopup ASAP and continue until dark, then 

patrol throughout the night. Be advised that visibility can 

deteriorate from clear to less than a few feet in less than 10 

minutes at night so constantly patrol nearby paved roads.

ExECUTING A SMOkE MANAGEMENT 

PlAN

OBTAIN AND USE FIRE WEATHER FORECASTS—

Fire weather forecasts contain information that is not 

commonly part of the general forecast provided in the 

radio/TV forecast. Smoke management information such 

as mixing height, transport winds, ventilation index and/

or dispersion index should be part of the forecast you use. 

Don’t rely on yesterday’s forecast, get an updated one the 

day of the burn. Do not routinely ask for a spot-weather 

forecast as they require significant effort to produce, but 

don’t hesitate to ask for one when you believe it is necessary 

for a successful burn.

DON’T BURN DURING POllUTION AlERTS 

OR STAGNATION CONDITIONS—Do not add to 

the problem. Such conditions are often reported in the 

discussion section of the fire weather forecast.

COMPlY WITH All AIR POllUTION CONTROl 

REGUlATIONS– Know the rules that apply at the 

proposed burn site. Check with the State fire control agency 

if unsure.

NOTIFY YOUR lOCAl FIRE CONTROl OFFICE, 

NEARBY RESIDENTS AND ADjACENT lAND 

OWNERS—This is common courtesy and can go a long 

way in reducing complaints, in addition it is required in 

most areas. People need to know that your fire is not 

a wildfire.

USE TEST FIRES TO CONFIRM BEHAvIOR OF 

BOTH THE FIRE AND ITS SMOkE—Test fires are 

often used to make certain that the fire behavior is within 

acceptable limits. Use these fires to make sure the smoke 

is doing what you expect which means a two minute 100 

square foot fire is not acceptable. The test fire should ideally 

be located within the burn unit, but if not, in similar fuels.

CONSIDER BACkING FIRES WHEN SMOkE IS 

AN ISSUE—Backing fires consume dead fuels more 

completely and produce less smoke. However, backing fires 

are not always the answer. 

• Backing fires are slow, which is a concern as this spreads 

the smoke out over a longer period thus making prediction 

more difficult as the weather is more likely to change 

(particularly the mixing height). Using a backing fire may 

require you to start your burn earlier, before the mixing 

height attains its predicted early afternoon value, thereby 

restricting combustion products to a shallower layer. A 

backing fire may also cause the burn to continue late into 

the afternoon when mixing heights will drop and trap smoke 

near the surface.

• Backing fires are lower intensity and therefore do not 

develop as strong of a convection column. The weak 

convection column limits smoke plume rise which keeps 

all of the smoke within the mixed layer. Other burning 

techniques can be used to produce more heat and loft smoke 

over nearby smoke sensitive targets.

TRY TO BURN DURING THE MIDDlE OF THE DAY

AND BE DONE WEll BEFORE SUNSET—Dispersion 

conditions are generally best at this time.

MOPUP AlONG ROADS—Start mopup along roads 

as soon as possible to reduce any impact on visibility. 

Extinguish all stumps, snags and logs. Be particularly 

aggressive when roads are in or near drainages that may 

channel smoke at night.

MONITOR YOUR SMOkE—Patrol the burn perimeter 

after burn and document where the smoke is/is not going.

HAvE AN EMERGENCY PlAN—Be prepared to 

extinguish the fire if the weather, fire behavior or smoke 

conditions are not within the ranges specified in the 

burn plan. Have warning signs available. Have contact 

information for local law enforcement.

kEEP IN MIND THAT THIS IS YOUR FIRE, AND THE 

SMOkE IS YOUR PROBlEM.

53

Planning the Prescribed 

Burn

The first step to a successful prescribed burn is a stand by 

stand analysis of your forest lands. Determine the needs of 

each stand and what actions should be taken to meet these 

needs. Prescribed fire as well as other alternatives should 

be addressed here and a decision reached regarding the 

preferred treatment. 

Prescription burning is a highly technical job requiring 

knowledge of fire behavior, suppression techniques and 

environmental effects of fire. Well in advance of the burning 

season, scout stands that may need a fire treatment and 

choose those to burn. The number of suitable burning days 

varies widely from year to year. Aerial ignition can be used 

to maximize the number of acres burned on each suitable 

burn day. Set priorities if you have several blocks to burn. 

Specifically designate any planned burns that require 

exacting weather conditions. Considerations include heavy 

fuels, small trees, potential smoke problems etc. Indicate 

all blocks to be burned on an administrative map. When the 

burns are completed, record the dates on the map.

A written prescribed burn plan prepared by a knowledgeable 

person is needed for each area to be burned. Complete the 

plan before the burning season and be prepared to burn 

when the prescribed weather conditions occur. Some of the 

plans may be quite short and simple while others will be 

long and complex. Individual blocks can vary from a few 

acres to over a thousand, but topography and amount/type 

of fuel should be similar in a unit. Your plan can consist of 

a series of blocks in the same compartment or management 

unit as long as the same objectives apply and the fuel 

is similar.

THE WRITTEN PlAN

A prepared form with space for all needed information is 

best. The form will serve as a checklist to be sure you have 

not overlooked some aspect or potential impact. Sample 

forms for both understory burns and post-harvest burns can 

be found at the end of this chapter. Contents of the written 

plan should include:

REqUIRED SIGNATURES—Provide spaces for 

signature(s) of person(s) who prepared the plan. This 

identifies the people who know the most about the plan.

PURPOSE AND OBjECTIvES—Include in the written 

plan the reason for prescribing fire as a treatment for this 

piece of land. Examples include: prepare seedbed, control 

insects or disease, reduce hazardous fuels, improve wildlife 

habitat, control understory, improve forage, increase 

accessibility and enhance aesthetics. In addition, include 

one or more specific, quantifiable objectives. State exactly 

what the fire will do—what it should kill or consume, how 

much litter/duff should be left, etc. Also, concisely describe 

the expected fire behavior, including desired range of flame 

lengths and fireline intensities. In case prescribed weather 

conditions do not materialize, this description may allow 

the objective(s) to still be achieved by varying the firing 

technique. This information will also be useful in evaluating 

the success of a burn.

MAP OF THE BURNING UNIT—A detailed map of each 

burn unit is an important part of the burn plan. The map 

should show the boundaries of the planned burn, adjacent 

land owners, topography, control lines (both existing and 

those needing construction), anticipated direction of the 

smoke plume, smoke-sensitive features, holding details 

and other essential information. Plowed control lines are 

often not necessary. Consider expanding the planned burn 

to employ existing fire breaks and natural barriers. For 

example, use fuel type boundaries such as occur near creek 

bottoms where the fire will go out as it encounters fuels with 

higher moisture content. Show areas that should be excluded 

Burning unit map

55
56

EqUIPMENT AND PERSONNEl—List equipment 

and personnel needed onsite and on standby with assigned 

duties.

FIRE PRESCRIPTION—The amount of fuel, weather 

conditions and desired intensity of the burn will determine 

the firing technique and ignition pattern to use to meet the 

burn’s objectives. Species involved and height of overstory 

will determine the maximum intensity that can be tolerated. 

Where large amounts of fuel are present, cooler burns can be 

accomplished by burning when humidity and fuel moisture 

are near the high end of the range so a smaller fraction of 

the fuel will be consumed. Lower temperatures are desirable 

with more intense fires, especially when understory fuels are 

tall, to limit the potential for crown scorch.

Behave-plus (http://www.firemodels.org/content/

view/30/39/) is a useful program for predicting fire behavior 

values to include in a burn plan. The calculations are based 

on data about fuels, weather, and topography. Important 

to look at potential fire behavior in the burn unit and in 

surrounding areas to aid in contingency planning for a 

possible escaped fire.

SEASON

WINTER—Most understory burning is done during the 

winter dormant season when acceptable fuel/weather 

conditions are most frequent. Good for high fuel loads.

SPRING—Weather and fuel conditions are more variable 

and often fire danger is higher, particularly in late spring. 

Also must consider potential impact on nesting wildlife. 

Vegetation can be more susceptible to heat damage 

(pine buds).

SUMMER—Hot weather during the summer means that 

less heat is required to raise the temperature of plant tissue 

to lethal levels. For this reason summer burns are often used 

to kill undesirable hardwoods. Care must be taken to avoid 

damaging overstory crowns. Late summer is a good time for 

post-harvest burns as the high temperatures help dry out the 

larger material.

FAll—Exercise care when burning in early fall just prior 

to the dormant season. Both loblolly and slash pine are more 

likely to die if severely scorched or root damaged at 

this time.

TIME OF DAY—Normally, plan prescribed burn operation 

so that the entire job can be completed within a standard 

workday. Prescribed fires are typically ignited between 10 

a.m. and noon, after any morning dew has had a chance to 

evaporate and any surface inversion from the previous night 

has lifted. If the forecast is for poor nighttime dispersion, 

halt ground ignition before 3 p.m. Halt aerial ignition before 

4 p.m. to allow adequate time for the fire to burn out before 

atmospheric dispersion conditions deteriorate.

Burning conditions are usually better during the day than 

at night because wind speeds are higher, wind directions 

are more steady, and an unstable atmosphere favors the 

vertical dispersion of smoke. These conditions make smoke 

management much easier during the day. At night smoke 

tends to stay near the ground and collects in depressions. 

Also, relative humidity is higher at night, resulting in spotty 

burning and an increased likelihood of fog formation.

However, on some winter nights when a strong cold front is 

moving through the area, winds remain strong and persistent 

and relative humidity does not rise greatly. These conditions 

can provide good prescribed burning conditions especially 

when cooler temperatures are needed. Whenever night 

burning is done, keep a close watch on the weather and 

smoke drift.

FIRING PlAN—Key parts for a successful prescribed burn 

are plans for firing and holding the burn. This plan should 

consist of a narrative section and a detailed map (the burn 

unit map is ideal for this). Important information to include:

• Firing technique, ignition pattern and planned 

ignition time.

• Manpower and equipment needed and planned distribution 

for setting, holding, patrolling and mopping up the fire and 

managing the smoke.

• Location and number of reinforcements and equipment 

that can be mobilized rapidly in the event that the fire 

escapes. Also include location of water sources.

• Instructions for all supervisory personnel, including 

complete description or illustration of assignment, and 

forces needed to fire, hold and mop up the fire.

AlTERNATIvE PRESCRIPTION—Consider alternative 

sets of weather and fuel conditions, along with firing 

techniques that will produce a fire of roughly the same 

intensity and accomplish the desired objectives. Sometimes 

this alternative may require two separate burns when dealing 

with heavy fuel loads.

or protected such as improvements, young reproduction, 

threatened and endangered species, etc. Subdivide areas 

into logical, 1-day burning blocks or smaller areas if smoke 

management dictates.
PREPARATION WORk AND PROTECTION OF 

SENSITIvE FEATURES—Include the fire lines to be 

constructed, snags to be lined or felled, special features to be 

protected and the installation of any monitoring equipment. 

Give instructions for the protection of sensitive areas. 

Consider historical and archeological sites, streams, habitats 

of threatened and endangered species, and fragile soils.

NOTIFICATION OF INTENT TO BURN—List the names 

and telephone numbers of the local State fire protection 

officer and other officials who should be contacted prior to 

the burn. Make direct contact with all homes and businesses 

in the area likely to be impacted by the burn. Consider 

written notification explaining the reasons for the burn and 

encouraging those with respiratory problems to contact 

you – include a telephone number for them to use. Offer to 

evacuate anyone with respiratory problems during the burn 

(consider putting them up in a hotel if necessary). Establish 

responsibility for burn-day contacts and how they will be 

made. Consider a newspaper article describing the reasons 

for the burn if you expect to produce lots of smoke and 

anticipate negative reactions.

IMPACT OF SMOkE—List any sensitive areas near to, 

downwind, or down drainage of the burn unit. Include 

smoke management strategies (avoidance, emissions 

reduction, dispersal) used to minimize adverse impacts 

at these sites. Attach the smoke management plan (e.g. 

screening system calculations) as part of the burn plan.

lEGAl REqUIREMENTS—List any legal requirements 

that might apply and what the prescribed burner must do to 

comply. Remember, the person conducting the prescribed 

burn may not be the one who conducted the analysis and 

wrote the prescription. Follow all applicable statutes, 

regulations and agency procedures. The need for a written 

prescribed burning plan, documentation of deviations from 

the plan, and good judgment cannot be overemphasized. 

Erroneous forecasts, unforeseen local influences, and 

accidents occur despite our best efforts to prevent them. 

Proper documentation will help establish that the prescribed 

fire was conducted in a prudent and professional manner. If 

a prescribed fire results in damage or bodily harm and you 

cut corners, neglected any mandatory requirements, or acted 

with disregard to the welfare of others, you are likely to be 

held responsible, regardless of whether compliance would 

have changed the outcome. For more information see the 

summary article, Legal Implications of Prescribed Burning 

in the South by William C. Seigal, listed in the Suggested 

Reading section.

ESCAPED FIRE PlAN—Identify potential fire escapes 

and specify actions to take in the event such an escape 

occurs. Designate who will be in charge of suppression 

action and what personnel and equipment will be available. 

Using Behave-plus to estimate potential fire behavior in 

areas adjacent to the burn unit can help in determining 

suppression needs.

CONTROl AND MOP UP—The plan must include 

necessary safeguards to confine the fire to the prescribed 

area and reduce smoke impact. Mop up promptly and 

completely when practical. Consider and make plans for any 

variation in forecasted weather that may change a prescribed 

fire into a damaging wildfire, increase the pollution in 

smoke-sensitive areas, or create a visibility problem on 

adjacent roads.

EvAlUATION—Include space for a written evaluation 

of the prescribed burn. A record of actual and forecasted 

weather conditions, fire behavior, and total environmental 

effects of the burn is essential. This information is used to 

determine if the objectives of the burn were achieved and 

can help in planning future burns.

At the beginning of the prescribed burn, record the 

forecasted weather and current conditions (wind speed and 

direction, temperature, relative humidity, fuel moisture, days 

since and amount of last rain and the dampness of the litter 

and duff). Documenting that weather conditions are within 

the acceptable ranges specified in the prescription is critical 

to supporting ones decision to burn. Also, fire behavior 

information such as the firing technique, flame length and 

forward rate of spread should be recorded to document that 

the fire behavior matches expectations. Continue to record 

this weather and fire information periodically throughout 

the burn. After the burn record the amount of crown scorch, 

consumption of brush, litter and duff, and any 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 include a short narrative on the success 

of the burn.

57
58

Simple Understory Prescribed Burning Unit Plan

Landowner Permit no. 

Address Phone no. 

S T R County Acres to burn Previous burn date 

Purpose of burn 

(Draw map on back or attach)

 

Stand Description

Overstory type & Size Height to bottom of crown 

Understory type & height 

Dead fuels: description and amount 

Preburn Factors 

Manpower & equipment needs 

List smoke-sensitive areas & locate on map 

Special precautions 

Estimated no. hours to complete Passed smoke screening system 

Adjacent landowners to notify 

 

Weather Factors: Desired Range Predicted Actual

Surface winds (speed & dir.) _______________________ ____________________________

Transport winds (speed & dir.) _______________________ ____________________________

Minimum mixing height _______________________ ____________________________

Dispersion/stagnation index _______________________ ____________________________

Minimum relative humidity _______________________ ____________________________

Maximum temperature _______________________ ____________________________

Fine-fuel moisture (%) _______________________ ____________________________

Days since rain Amount _______________________ ____________________________

 

Fire Behavior: Desired Range Actual

Type fire 

Best month to burn Date burned 

Flame length 

Rate of spread 

Inches of litter to leave 

Evaluation: Immediate Future

Any escapes? Acreage Evaluation by 

Objective met Date 

Smoke problems Insect/disease dam. 

% of area with crown discoloration of Crop Tree Mortality 

5-25% 26-50% 51-75% 76%+ % understory kill 

Live crown consumption Soil movement 

% understory veg. consumed Other adverse effects 

Adverse publicity 

Technique used OK Remarks 

Remarks 

 

 

 

 

 

 

 

Prescription made by 

Title Date / / 
Understory Prescribed Burning Unit Plan

Prepared by Signature Date Permit no. 

State County District Comp’t 

Burning unit no. S T R Gross acres Net acres 

Landowner Address & phone no. 

Person responsible & how to contact day & night 

(Draw map on back or attach)

A. Record of Previous Burning: Date Fire type Results 

B. Description of Stand:

1. Overstory: Type, density, size Height to bottom of crown 

2. Understory: Type, density, height 

3. Dead fuels: Type, density, age, volume 

4. Soil type and topography 

C. Purpose(s) of Burn: 

D. Specific Objectives: 

E. Preburn Factors:

1. Chains to plow (see map): Exterior Interior Total 

2. Chains to fire (see map): Exterior Interior Total 

3. Crew size: Equip. needs 

4. Estimated tons/acre Total tons to be burned 

5. Ignition procedure (see map) 

6. Passed screening system? Special precautions 

7. Notify: 

8. Regulations that apply 

9. List smoke-sensitive areas & critical targets (see map): 

F. Weather Factors: Desired Range Predicted Actual

1. Surface wind (speed & dir.) 

2. Transport wind (speed & dir.) 

3. Stability/stagnation index 

4. Minimum mixing height 

5. Dispersion index 

6. Minimum relative humidity 

7. Maximum temperature 

8. Fine-fuel moisture 

9. Days since rain Amount 

10. Burning index Drought index 

G. Fire Behavior: Desired Range Actual Range

1. Type fire 

2. Best month to burn Date burned 

3. Time of day to start Time set 

4. No. of hours to complete Completed 

5. Flame length 

6. Rate of spread 

7. Fireline intensity 

8. Inches of litter to leave Litter left 

H. Evaluation Immediately After Burn: Future Evaluations:

1. Acres burned Evaluation by 

2. Spotting Distance Date made 

3. Any escapes Insect/disease dam. 

4. Objectives met 

5. Smoke problems Crop tree morality 

6. % understory veg. consumed 

7. % of area with crown discoloration of % Understory kill 

0 5-25% 26-50% 51-75% 76%+ Soil movement 

8. Live crown consumption Other adverse effects 

9. Adverse publicity 

10. Remarks Remarks 

59
60

Postharvest Prescribed Burning Unit Plan

Prepared by Signature Date Permit no. 

State County District Comp’t

Burning unit no. S T R Gross acres Net acres 

Landowner Address & phone no. 

Person responsible & how to contact day & night 

(Draw map on back or attach)

A. Description of Area:

1. Natural stand or plantation Stand age Harvest date 

2. Clearcut Harvest method Pine basal area removal 

3. Organic soil Hardwood basal area Hardwoods utilized 

4. Unmerchantable trees felled Snags felled Debris evenly distributed 

5. Debris (light, medium or heavy) Brush (light, medium or heavy) 

6. Herbaceous fuels (light, medium, heavy Herbaceous fuels continuous 

7. Herbicide used Date applied / / 

8. Drum chopped Single or double pass Date completed / / 

9. Windrowed and/or piled Date piled / / Piled when wet 

10. Pile of windrow dimensions: Ht. Width (dia.) 

11. Windrow break interval 

B. Preburn Factors and Desired Fire Intensity:

1. Areas to exclude 

2. Chains to plow (see map): Exterior Interior Total 

3. Chains to fire (see map): Exterior Interior Total 

4. Equipment needs 

5. Crew size Type of fire Type of ignition 

6. Ignition procedure (see map): 

7. No. of hours to complete Tons/acre to consume Litter to leave (in.) 

8. Special precautions: 

9. Notify: 

10. Regulations that apply 

11. Passed screening system? List smoke sensitive areas, critical targets & locate on map 

C. Weather Factors Desired Range Predicted Actual

1. Surface wind (speed & dir.) 

2. Transport wind (speed & dir.) 

3. Mixing height 

4. Dispersion Index (or comparable) 

5. Relative humidity (%) 

6. Temperature (°F) 

7. Fine-fuel moisture (%) 

8. 10-hr. fuel moisture (%) 

9. Days since rain Amount 

10. Burning index Drought index 

11. Best month to burn Dates burned 

12. Time of day to start Time set 

D. Summary of Burn:

1. Type fire & ignition 

2. All piles, windrows & logging decks ignited 

3. % of area burned Did area between piles burn? 

4. Spotting frequency Distance Firebrand material 

E. Evaluation Immediately After Burn:

1. Any escapes: Number Adjacent to burn area? Acres involved 

2. Hours to burnout: Active flaming Smoldering Total hours 

3. % understory veg. consumed Depth of litter remaining (in.) 

4. % material < 3” dia. consumed Did piled debris burn down? 

5. Objectives met 

6. Adverse publicity 

7. Smoke problems 

8. Remarks 

F. Future Evaluation (date, signature, and remarks) 
61

Preparing for the Prescribed 

Burn

Good preparation and a clear objective are the keys to 

successful burning and are essential in realizing maximum 

net benefits at acceptable costs. Preparation consists of all 

activities necessary to make an area ready for firing and 

having all needed tools equipment and information ready 

to go. Much of this work is conducted by the burn boss. To 

do this job skillfully, the burn boss should have personal 

knowledge or information available about:

• Weather elements involved

• Fire behavior

• Smoke management

• Amount and type of fuel on the area

• Location of natural and man-made fire barriers

• Degree of risk and hazard present

• Burning technique and intensity of fire to be used

• Burning objectives for the particular area

• Restrictive measures dictated by law or local custom

• Fire suppression safety

• Location of any improvements which could be endangered

• Areas within the prescribed unit that may need to be 

excluded from fire such as:

areas with extreme mop up or breakover potential 

 (sawdust piles, muck soils, snags, etc.)

 highly scenic areas

 highly erodible areas

 areas harboring special-quality wildlife or plant 

 communities that would be damaged by fire

 desirable hardwood areas

 timber and grass areas susceptible to fire damage

All site-specific information should be included in the 

written prescription. Before starting work, the burn boss 

should inspect the area by walking over it and should give 

safety instruction to all work crews.

ESTABlISHING CONTROl lINES

• Construct lines in advance of burning, preferably after 

leaf fall to reduce effect of fallen material on prepared 

lines. Control lines should reach mineral soil and can be 

constructed by plowing, disking, tilling or raking.

• Use existing barriers such as streams, logging roads, or 

cultivated fields whenever possible.

• Hold plow lines to a minimum, keeping them shallow and 

on the contour as much as possible in hilly terrain. Consider 

igniting from wet lines. Use skid trails and logging roads 

where feasible.

• Keep control lines as straight as possible. Bend them 

around excluded areas, avoiding abrupt changes in direction.

• Avoid rock outcrops and boggy ground.

• Double or widen control lines in hazardous places.

• Subdivide large areas into logical 1-day burning jobs.

• Avoid leaving dense timber stands or heavy fuel pockets 

near lines.

• Mow problem fuel spots near control lines to reduce 

potential spotovers.

AFTER CONTROl lINES ARE 

ESTABlISHED

• Remove any material above the line that could carry fire 

across the control line such as vines and overhanging brush.

• Fall snags near line (inside and outside) – this should be 

done judiciously and in consideration of the value to wildlife 

of the snag.

• Construct water bars and leadoff ditches in steeper terrain 

to prevent soil erosion.

• Seed and fertilize exposed soil with native or non-invasive 

species on control lines in steep topography to prevent 

soil erosion.

BURN UNIT MAP

• Locate all control lines on the map noting changes from the original plan.

• Note on the map any danger spots along control lines having potential for fire escape.
62

Eddies caused by forest openings.

Convections and eddies for open areas.
63

Post warning signs on public roads.

For any particular burn prescription there are only so many 

days in a year that will meet all of the burn’s criteria so 

the burn crew must be prepared for these opportunities. A 

typical burn crew consists of a burn boss and three to six 

crew members. The burn boss should be an experienced 

prescribed burner with an understanding of fire behavior. 

The other members of the crew will typically be divided 

into ignition and holding groups. If aerial ignition is used, a

minimal ignition crew consists of the pilot and an ignition 

specialist who is responsible for operating the ping-pong 

ball system. Good communication is essential for all 

prescribed burns, but especially for aerial ignition burns.

The burn boss should have the crew ready to fire the areas 

as early in the day as conditions permit, leaving maximum 

time for mop up and patrol of lines and to reduce chances 

of nighttime smoke problems. The burn boss must make 

sure that crew members are fit and have proper clothing and 

safety equipment. Proper clothing includes long-sleeve fire 

resistant or cotton shirts, pants without cuffs, leather boots 

with non-skid soles, safety glasses, hardhat, gloves and 

plenty of drinking water. During the summer, the possibility 

of heat exhaustion and heat stroke must be considered.

Executing the Burn

Conduct a test burn.
 Make sure all equipment is in working order 

and that it is safe to use

 Carry burn plans and maps to the site

 Have a means of instant communication 

with all crew members. Portable radios are 

very useful as are cellphones, but make sure 

that all sections of the burn unit have good 

reception.

 Check the weather before starting to burn 

and keep updated throughout the day

 Check all control lines, clean out needles 

and leaves and reinforce if necessary

 Notify adjoining property owners and local 

fire control organizations before starting fire

 Instruct crew on procedures, including 

safety precautions and the proper operation 

of equipment and use of hand tools

 Inform the crew of starting point and firing 

plan. Give each member a map.

CHECklIST

 Post signs on public roads and be prepared 

to control traffic if potential exists for smoke to 

reduce visibility

 Check duff and soil for dampness

 Test burn with a small fire before firing off 

the unit; check fire and smoke behavior and 

make sure they match expectations. If not, 

decide whether the observed fire /smoke 

behavior are acceptable. This is the time to 

cancel the burn if you are not comfortable 

with the observed behavior. Note on the plan 

the results of the test burn and your decision 

to burn or not.

 Be alert to changing conditions and be 

prepared to change burning techniques or 

plow the fire out if an emergency arises

 Burn so the wind will carry the smoke away 

from sensitive targets

 Mop up and patrol perimeters constantly 

during the operation and thereafter until there 

is no further danger of fire escape or smoke 

problems.

64
Burn evaluations are an important means for determining 

how well the the stated objectives of the burn were met as 

well as gaining information to be used in future burns. An 

initial evaluation should be made immediately after the 

burn, perhaps the following morning. A second evaluation 

should be made during or after the first postfire growing 

season.

GENERAl POINTS TO BE CONSIDERED

• Was preburn preparation properly done and adequate for 

the burn?

• Were objectives met?

• Was the burn plan followed? Were changes made 

and documented?

• Were weather conditions, fuel conditions, fire behavior 

and smoke dispersion within planned limits? Were any 

deviations documented?

• What were the effects on soil, air, vegetation, water 

and wildlife?

• Was the fire confined to the intended area; any escapes?

• Was the burning technique correct?

• Were costs commensurate with benefits derived?

• What could be done to improve similar burns next time?

POINTS IN FIRST EvAlUATION

• Amount of overstory foliage discoloration

• Amount of consumption and top-kill of 

understory vegetation

• Amount of litter/duff remaining on forest floor

• Amount of mineral soil exposed

• Impacts to non-target species

• Degree of success in avoiding smoke-sensitive features

• Protection of areas not to be burned; any escapes?

Evaluating the Burn

• Any adverse public comment or reaction prior to, during or 

immediately after the burn

POINTS FOR SECOND EvAlUATION

• Resin exuding from pine trees, an indicator of cambrium 

damage or insect attack

• Signs of disease or insect damage

• Mortality of timber or other desirable vegetation

• Sprouting vigor of undesired vegetation

• Remaining duff layer, mineral soil exposed, and any 

soil movement

• Public expression for or against the burning program

• Ground cover response

• Invasive species

• Impacts to target species

INDICATIONS AND GUIDElINES

Needle SCorCh—The best indicator of crop tree 

damage is percent of foliage discoloration. Assuming that 

buds and branchlets are not heat-killed, even crown scorch 

approaching 100 percent generally will not kill trees unless 

secondary factors such as insect attacks, disease or drought 

materialize. However, loblolly pine stands burned in the fall 

after their last needle flush prior to dormancy, are likely to 

be killed by 100 percent crown scorch. Slash pine appears to 

be more tolerant of severe crown scorch during the fall.

If more than 15 percent of a southern pine tree’s needles are 

actually consumed by flames, the tree’s chances of survival 

would be poor even if very little of the rest of the crown is 

scorched. Young vigorous trees are more likely to survive 

severe crown damage than are older individuals.

Percent Crown Scorch Damage 

0 to 33 Some volume growth loss may occur the first postfire growing 

season but it will be minor. 

34 to 66 Volume growth loss usually less than 40 percent and confined to the 

first postfire growing season. 

67 to 100 Reduction may be as high as a full year's volume growth spread 

over 3 years. 

65
66

Magnitude and duration of growth responses in southern 

pines due to various levels and seasons of defoliation are not 

well documented. Both negative and positive responses have 

been observed, but the preponderance of evidence shows a 

direct relationship between diameter and height growth loss 

and crown scorch. Providing no crown consumption occurs, 

the following table will help estimate potential growth loss 

in loblolly and slash pines over 3 inches dbh. These “ball 

park” estimates can be used for other southern pines as well, 

until more specific results become available.

A good indicator of hardwood control is a series of bark 

cracks extending into the cambrium near ground level. This 

indicates sufficient heat was applied to penetrate the bark 

and kill the cambrium. Although large hardwoods can be 

damaged by periodic fires, they are hard to kill.

Judge the success of burning for brownspot control by 

the number of longleaf seedlings with all infected needles 

burned off, but still having a protective sheath of green 

needles around an unharmed terminal bud.

SOIl AND ROOT DAMAGE—Burning under prescribed 

conditions in the South generally does not expose much bare 

soil. If duff remains after a burn, the physical properties 

of the soil were probably not harmed. If mineral soil is 

exposed, especially on steep slopes, soil movement and 

deterioration of site quality may occur.

Root damage is likely whenever the organic layer is 

completely consumed. It should also be expected whenever 

Post-burn evaluation helps to determine if the objectives of the fire 

were met.

burns are conducted over dry soils (drought conditions) 

or when a deep litter layer is present. New root growth in 

vigorously growing pines can usually offset losses, but older 

trees, having survived such fires without crown damage, 

often die six months to a year later for no apparent reason.

AIR qUAlITY—Smoke behavior must be continually 

monitored from the time the fire is ignited until smoldering 

ceases. Unusual or unexpected smoke plume behavior 

should be noted and correlated with other parameters of the 

burn for future reference. Any public complaints should be 

recorded as part of the evaluation. 
Coordination of 

Burning These guidelines are general and will not fit all situations.

PURPOSE TIME OF BURN SIZE OF BURN TYPE OF FIRE FREQUENCY REMARKS

REDUCE FUELS Winter Large enough to 

break fuel continuity

Not critical. Do 

not ring fire

2 to 4 years Use line-backing fire, or point 

source fires under moist 

conditions for initial burn. Gridfiring technique excellent for 

maintenance burns. 

IMPROVE 

WILDLIFE 

HABITAT

General—Protect transitional or 

fringe areas. Do not burn stream 

bottoms.

Deer Winter preferred Small or leave 

unburned areas

Backing fire or 

point-source 

fires

2 to 4 years Want to promote sprouting and 

keep browse within reach. Repeat 

summer fires may kill some 

rootstocks.

Turkey Winter preferred; 

summer burns in 

July - August

Small or leave 

unburned areas

Backing fire or 

point-source 

fires 

2 to 4 years Avoid April through June nesting 

season.

Quail Late winter 25+ acres Not critical. Do 

not ring fire

1 to 2 years Avoid April through June nesting 

season. Leave unburned patches 

and thickets.

Dove Winter Not critical Not critical. Do 

not ring fire

Not critical Leave unburned patches and 

thickets.

Waterfowl Late fall or winter Not critical Heading fire 2+ years Marshland only. Do not burn in 

hardwood swamps.

CONTROL 

COMPETING 

VEGETATION

Heavy roughs in 

winter, otherwise 

not critical

Not critical Not critical. Do 

not ring fire

2 to 8 years Summer burns result in higher 

rootstock kill and affect larger 

stems. Exclude fire from desirable 

hardwoods in pine-hardwood type.

IMPROVE 

FORAGE FOR 

GRAZING

Winter through late 

spring for most 

situations

Not critical but will 

be damaged by 

overuse if too small 

for herd.

Not critical. Do 

not ring fire

3 years Split range and burn one-third 

each year. Individual herbs and 

grasses respond differently to fire 

and season of burn. Consult 

expert.

IMPROVE 

ACCESSIBILITY

Will vary with 

understory and 

desired use

Varies with 

individual situation

Depends on 

amount of fuel 

present

As needed Coordinate with other resource 

objectives. They will dictate size, 

timing and frequency of burn. 

CONTROL 

DISEASE

Brownspot, winter Depends on size of 

infected area. 

Include a buffer strip

Strip-heading or 

heading fire

2 to 3 years Burn when humidity is above 50%. 

Avoid leaving unburned pockets of 

infected seedlings within of 

adjacent to burn.

67
68

PURPOSE TIME OF BURN SIZE OF BURN TYPE OF FIRE FREQUENCY REMARKS

ENHANCE 

APPERANCE

Late fall through 

late winter

Varies with each 

situation

Backing fire or 

Point-source fire

1 + years Requires precise prescription to protect 

vegetative type changes. Know effect of 

fire frequency and season of burn on 

both annual and biennial flowering 

plants. Provide pleasing visual lines.

PERPETUATE 

FIRE 

DEPENDENT 

SPECIES

Will vary with 

species

Will vary with 

species

Will vary with 

fuel conditions 

and species 

requirements.

Will vary with

species

Fire intensity, timing and frequency all 

dictated by species requirements.

YOUNG PINE 

STANDS

Winter Varies with size of 

stand

Backing fire 2 to 4 years Pine diameter 3 inches or more at 

ground. Pine height above 10 ft. Burn 

only after a strong cold front with rain.

DISPOSE OF 

LOGGING 

DEBRIS

Not critical Small areas mean 

fewer nighttime 

smoke problems

Center firing with 

helicopter

preferred

__ Smoke management is a must! Take 

care not to damage soil or water 

resources with these hot fires. If a 

broadcast burn will not meet objectives, 

pile–do not windrow debris. 

PREPARE 

SITES FOR 

SEEDING

Natural seeding, 

summer to early 

fall prior to seed 

fall.

Large enough to 

prevent 

concentrations of 

birds & rodents 

(usually 10 acres 

or more). 

Not critical. Do 

not ring fire

__ 

Be careful not to kill seed trees. If 

logging debris present, manage your 

smoke.

Direct seeding, 

fall to late winter 

for spring sowing. 

Previous winter 

for fall sowing of 

longleaf.

Large enough to 

prevent 

concentrations of 

birds & rodents 

(usually 10 acres 

or more). 

Not critical. 

Center firing with 

helicopter 

preferred if slash 

present.

__ 

If logging debris present, smoke 

management is a must! Take care not 

to damage soil or water resources with 

these hot fires

PREPARE 

SITES FOR 

PLANTING

Growing season 

for hardwood

Large enough to 

prevent 

concentrations of 

birds & rodents 

(usually 10 acres 

of more). 

Not critical. 

Center firing with 

helicopter

preferred if slash 

present.

__ 

If logging debris present, smoke 

management is a must! Take care not to 

damage soil or water resources with 

these hot fires
69

1. Observe and follow all local laws and guidelines.

2. Obtain and use latest weather and smoke 

management forecasts. 

3. Relative humidity will roughly halve with each 20° F 

increase in temperature in a given air mass. 

4. Expect increased spotting when relative humidity drops 

below 30 percent. 

5. Burn when mixing height is above 1,650 feet 

(500 m). 

6. Do not burn under temperature inversions. 

7. Never underburn during a drought. Soil moisture is 

needed to protect tree roots and lower litter. 

8. Don’t burn on organic soils unless the water table is very 

close to the surface. 

9. Heading fires produce about three times more particulate 

than backing fires. 

10. Burn when fuels are dry, but not too dry. Wet fuels 

produce substantially more particulate than do dry fuels. 

11. Start burning logging debris by midmorning. 

12. Site prep burning behind chopping or other mechanical 

treatment gives best results if done 10 to 15 days 

after treatment. 

General Rules

13. Windrows are the most polluting of all southern 

fuel types. 

14. Broadcast burn scattered debris if possible. 

15. Do not pile debris when either ground or debris is wet. 

16. Dirt in piled debris will increase the amount of smoke 

produced by up to four times. Shake out dirt while piling; 

“bump” piles while burning, and re-pile as necessary. 

17. Use a smoke management plan. Consider smoke 

sensitive areas. Look several miles downwind and downdrainage for potential targets. 

18. If nighttime Dispersion Index forecast is very poor (less 

than 6), try to have burning complete two hours before 

sunset to limit the amount of smoke trapped under the 

nocturnal inversion. 

19. Doubling the Dispersion Index implies a doubling 

of the atmospheric capacity to disperse smoke within a 

1,000-square-mile area. 

20. Assuming 1 ton of fuel per acre is being consumed by 

smoldering combustion during poor nighttime dispersion 

conditions, expect visibility in the smoke to be less than 1/2

mile within 1 1/2 miles of the fire. 

21. Be familiar with all topographic features in the burn unit 

to understand how wind direction and fire behavior 

may change.

22. A fire escape contingency plan is an important part of the 

prescription process.
If any of the following conditions exist, analyze further 

before burnings.

UNDERBURNING:

• No written plan 

• No map 

• No safety briefing 

• Heavy fuels 

• Dry duff and soil 

• Extended drought 

• Inadequate control lines 

• No updated weather forecast for area 

• Forecast does not agree with prescription 

• Poor visibility 

• Inadequate personnel or equipment 

• Burning large areas using aerial ignition

• Communications for all crew members not available 

• No backup plan or forces available 

• No one notified of plans to burn 

• Behavior of test fire not as prescribed 

• No smoke management plan

• Smoke-sensitive area downwind or down drainage 

• Organic soil present 

• Daytime Dispersion Index below 40 

• Not enough personnel or equipment available to control an 

escaped fire 

• Personnel on fire not qualified to take action on 

escaped fire

DEBRIS BURNING - IN ADDITION TO THE ABOvE:

• Area contains windrows 

• A lot of dirt in piles 

• Poor nighttime smoke dispersion forecast 

• Have not looked down drainage 

• Mixing height is below 1,650 feet (500 m) 

• Debris was piled when wet 

• Pile exteriors are wet 

IF ANY OF THE FOllOWING CONDITIONS ExIT, 

STOP BURNING AND SUPPRESS ExISTING FIRE.

• Fire behavior erratic 

• Spot fire or slop-over occurs and is difficult to control 

• Wind shifting or other unforeseen change in weather 

• Smoke not dispersing as predicted

• Smoke impacting a public road or other sensitive area 

• Burn does not comply with all laws, regulations, 

and standards 

• Large fuels igniting and burning, not enough personnel to 

mopup before dark and likely to smoke in a smoke 

sensitive area. 

Red Flag Situations

70
71

Aerial Fuels - Standing and supported live and dead 

forest combustibles not in direct contact with the ground 

consisting mainly of foliage, twigs, branches, cones, bark, 

stems, and vines (See Draped Fuels, Ladder Fuels)

Aerial Ignition - Ignition of fuels by dropping incendiary 

devices or materials from aircraft.

Age of rough - Time in years since the forest floor was last 

reduced by fire.

Air Stagnation Advisory (ASA) - A statement issued 

by a National Weather Service office when atmospheric 

conditions are stable enough that the potential exists for 

pollutants to accumulate in a given area.

Anemometer - General name for instruments designed to 

measure windspeed.

Area Ignition - Igniting, throughout an area to be burned, 

a number of individual fires either simultaneously or in 

rapid succession and so spaced that they soon influence 

and support each other to produce a hot, fast-spreading fire 

throughout the area.

Aspect - Direction toward which a slope faces.

Atmospheric Stability - A measure of the degree to which 

the atmosphere resists turbulence and vertical motion. In 

prescribed fire activities the atmosphere is usually described 

as stable, neutral, or unstable.

Available Fuel - That portion of the total fuel that will be 

consumed under a specific set of burning conditions.

Backing Fire - A fire spreading or set to spread into 

(against) the wind, or downhill. (See Flanking Fire, 

Heading Fire).

BehAVe PlUS - A user friendly computer system to 

predict fire bevavior.

Belt Weather Kit - Belt mounted canvas case with fitted 

pockets for anemometer, compass, sling psychrometer, slide 

rule, water bottle, pencils, and book of weather report forms.

Blackline - Preburning of fuels, either adjacent to a control 

line before igniting the main prescribed fire, or along a 

roadway as a deterrent to human-caused fires. Blackline 

denotes a condition in which there is no unburned fine fuel.

Glossary

Broadcast Burn - Prescribed fire that burns over a 

designated area, generally in the absence of a merchantable 

overstory, to consume debris that has not been piled 

or windrowed.

Brown and Burn - Application of herbicide to desiccate 

living vegetation prior to burning.

Brownspot Control - A prescribed burn to control a fungal 

infection (brownspot disease) of longleaf pine in the “grass” 

(small seedling) stage.

Buildup - Cumulative effects of long-term drying on current 

fire danger.

Buildup Index (BUI) - A relative number expressing the 

cumulative effect of daily drying factors and precipitation 

on fuels with a 10-day timelag constant.

Burn Boss - Person responsible for managing a prescribed 

fire from ignition through mopup.

Burning Index (BI) - A relative number related to the 

contribution fire behavior makes to the amount of effort 

needed to contain a fire within a given fuel type. A doubling 

of the BI indicates twice the effort will be needed to contain 

a fire in that fuel type as was previously required.

Category day - A numerical index related to the ability of 

the atmosphere to disperse smoke. For example, in South 

Carolina the current scale, based on Ventilation Factor, 

ranges from 1 (poor) to 5 (excellent).

Center Firing - A method of broadcast burning in which 

fire(s) are set in the center of the area to create a convection 

column with strong surface indrafts. Usually additional fires 

are then set progressively nearer the outer control lines as 

the indraft builds up, to draw the flames and smoke toward 

the center of the burn.

Chain - Unit of measure in land survey equal to 66 feet; 80 

chains equal 1 mile.

Clearcutting - Removal of the entire standing, 

merchantable timber crop.

Cold Front - The leading edge of a mass of air that is colder 

and drier than the air mass being replaced.
Control line - Comprehensive term for all constructed or 

natural fire barriers and treated fire edges used to control 

a fire. 

Convection Column - The rising column of gases, smoke 

and debris produced by a fire. The column has a strong 

vertical component indicating that buoyant forces override 

the ambient surface wind (See Smoke Plume).

Convergence Zone - The area of increased flame heights 

and fire intensity produced when two or more flame fronts 

burn together.

Crown Scorch - Browning of needles or leaves in the crown 

of a tree or shrub caused by heat from a fire.

Cured - Debris or herbaceous vegetation that has dried and 

lost its green color.

dAId (delayed Aerial Ignition device) - See Ping-pong 

Ball System.

debris Burning - In this publication, defined as any 

prescribed fire used to dispose of scattered, piled, or 

windrowed dead woody fuel in the absence of an overstory. 

Such a burn often accomplishes the objectives of a Site Prep 

Burn as well.

dew Point - Temperature to which air must be cooled to 

reach saturation at a constant atmospheric pressure. The 

dew point is always lower than the wet-bulb temperature, 

which in turn is always lower than the dry-bulb temperature. 

The only exception to this is when the air is saturated (i.e., 

relative humidity is 100 percent), in which case all three 

values are equal.

dispersion - The decrease in concentration of airborne 

pollutants as they spread throughout an increasing volume 

of atmosphere.

dispersion Index - A numerical index to estimate the 

atmosphere’s capacity to disperse smoke from prescribed 

burns over a thousand square mile area. It is related to 

the Ventilation Factor, but also considers the impact of 

atmospheric stability on pollutant dispersal.

draped Fuels - Needles, leaves, twigs, etc., that have fallen 

from above and have lodged on lower branches and brush. 

Part of aerial fuels.

drift Smoke - Smoke that has been transported from its 

point of origin and in which convective motion no longer 

dominates.

drip Torch - Hand-held apparatus used to ignite fires by 

dripping flaming liquid fuel, at an adjustable rate, on the 

materials to be burned. The fuel is generally a mixture of 65 

to 80 percent diesel and 20 to 35 percent gasoline.

drought Index (Keetch-Byram drought Index) - A 

numerical rating of the net effect of evapotranspiration and 

precipitation in producing cumulative moisture depletion in 

deep duff or upper soil layers.

dry-bulb Temperature - The temperature of the air.

duff - The layer of decomposing organic materials lying 

below the litter layer and immediately above the mineral 

soil. It is comprised of the Fermentation (F) and Humus (H) 

layers of the forest floor.

edge - As used in this manual, the boundary between two 

fairly distinct fuel types.

emission Factor - The amount of pollution (pounds per 

ton) released to the atmosphere per unit weight of dry fuel 

consumed during combustion.

emission rate - The quantity of pollutant released to the 

atmosphere per unit length of fire front per unit time.

equilibrium Moisture Content (eMC) - The moisture 

content that a fuel would eventually attain if exposed for 

an infinite period to specified constant values of dry-bulb 

temperature and relative humidity.

Fine Fuels (Flash fuels) - Fast-drying, dead fuels which 

have a timelag constant of 1 hour or less. These fuels ignite 

readily and are consumed rapidly when dry. Included are 

grass, leaves, draped pine needles, and small twigs.

Fire Behavior - A general term that refers to the combined 

effect of fuel, weather and topography on a fire.

Firebrand - Any flaming or smoldering material such as 

leaves, pine cones, or glowing charcoal that could start 

another fire.

Firebreak - Any natural or constructed discontinuity in a 

fuelbed used to segregate, stop, or control the spread of fire 

or to provide a control line from which to suppress a fire.

Fire effects - Physical, biological and ecological impacts of 

fire on the environment.

Fire Front - The strip within which continuous flaming 

occurs along the fire perimeter (See Flame Depth).

72
73

Fireline Intensity (Byram’s Intensity) - The rate of 

heat release per unit time per unit length of fire front. 

Numerically, it is the product of the heat yield, the quantity 

of fuel consumed in the fire front, and the rate of spread.

Fire Plow - Heavy-duty share or disk plow designed to be 

pulled by a tractor to construct firebreaks.

Fire rake - A long-handled combination rake and cutting 

tool, the blade of which is usually constructed of a single 

row of 4 sharpened teeth.

Firing Technique - The type(s) of fire resulting from one or 

more ignition(s), e.g., backing fire, flanking fire, heading fire 

(See Grid Ignition, Ignition Pattern).

Flame depth - The depth of the fire front at the fuel surface.

Flame length - The distance between the flame tip and 

the midpoint of the flame depth at the base of the flame 

(generally at the ground surface).

Flanking Fire - A fire front spreading, or set to spread at 

roughly right angles to the prevailing wind.

Flash Fuels - See fine fuels. 

Fuel Moisture Content - Water content of a fuel expressed 

as a percentage of the oven-dry weight of the fuel.

Fuel Moisture Indicator Sticks - A specially manufactured 

set of sticks of known dry weight continuously exposed to 

the weather and periodically weighed to determine changes 

in moisture content. The changes are an indication of 

changes in the moisture status and relative flammability of 

dead fuels that roughly correspond to Ten-hour 

Timelag Fuels.

Grid Ignitions - Method of igniting fires in which ignition 

points are set individually at predetermined spacing with 

predetermined timing throughout the area to be burned (see 

Ping-pong Ball System).

hazard reduction - Treatment of living and dead forest 

fuels to reduce the likelihood of a fire starting and to lessen 

its damage potential and resistance to control.

heading Fire - A fire front spreading or set to spread with 

the wind or upslope.

herbaceous Fuels - Grasses and other plants that contain 

little woody tissue.

humus - The layer of decomposed organic matter on the 

forest floor beneath the partially decomposed litter layer (F 

layer) and directly above the soil.

hygrothermograph - An instrument that continuously 

records dry-bulb temperature and relative humidity.

Ignition Pattern - The manner in which a prescribed fire 

is ignited. The distance between ignition lines or points 

and the sequence of igniting them, as determined by fuel, 

topography, weather, ignition system, firing technique, and 

other factors influencing fire behavior and the objectives of 

the burn (See Firing Technique).

In-stand Wind (Midflame Wind) - Windspeed within a 

stand at about eye level.

Inversion - In this publication, defined as a layer of the 

atmosphere through which the temperature increases with 

increasing height.

Keetch-Byram drought Index - See Drought Index.

ladder Fuels - Fuels that provide vertical continuity 

between the ground and tree crowns, thus creating a 

pathway for a surface fire to move into the overstory tree 

crowns.

line Ignition - Setting a line of fire as opposed to

individual spots.

litter - The top layer (L layer) of the forest floor directly 

above the fermentation layer (F layer), composed mainly 

of recently fallen leaves and pine needles, but also includes 

dead twigs, bark fragments, etc. (See Duff).

logging debris - Unwanted tree parts remaining after 

harvest, including tree crowns, unutilized logs, and 

uprooted stumps.

low-level Jet - A rapid increase with height to a maximum 

wind speed within 1,000 feet above ground and then a slow 

decrease above that peak. One form of adverse wind profile.

Midflame Wind - See In-stand wind. 

Mineral Soil - Soil layers below the predominantly 

organic horizons.

Mixing height - The height to which relatively vigorous 

mixing of the atmosphere occurs.

Mopup - Extinguishing or removing burning material, 

especially near control lines after an area has burned to 

make it safe, or to reduce residual smoke.

Muck - See Organic Soil.
National Fire danger rating System (NFdrS) – A 

method to integrate the effects of topography, fuels, and 

weather into numerical indices of fire danger on a day-today basis.

one-hour Timelag Fuels - Fine fuels consisting mainly of 

dead herbaceous plants, sticks less than about 1/4-inch in 

diameter, and the uppermost litter layer.

organic Soil - Any soil or soil horizon containing at least 

30 percent organic matter; examples are peat and muck.

Particulate (Total Suspended Particulate (TSP) - Any 

liquid or solid particles temporarily suspended in the 

atmosphere. See PM-10 or PM-2.5.

Peat - See Organic Soil.

Ping-pong Ball System - A method of igniting fires with the 

use of a Delayed Aerial Ignition Device (DAID). The device 

is a polystyrene ball, 1.25 inches in diameter that contains 

a combustible chemical. The balls are fed into a dispenser, 

generally mounted in a helicopter, where they are injected 

with another chemical and drop through a chute leading out 

of the helicopter. The chemicals react thermally and ignite 

in about 30 seconds. The space between ignition points on 

the ground is primarily a function of helicopter speed, gear 

ratio of the dispenser, and the number of chutes used (up to 

4) (See Grid Ignition).

PM-10 - Particulate with an aerodynamic diameter smaller 

than or equal to 10 micrometers.

PM-2.5 - Particulate with an aerodynamic diameter smaller 

than or equal to 2.5 micrometers.

Prescribed Burning - fire applied in a knowledgeable 

manner to forest and grassland fuels on a specific land 

area under selected weather conditions to accomplish 

predetermined, well-defined management objectives.

Psychrometer - The general name for instruments designed 

to determine the moisture content of air. A psychrometer 

consists of dry and wet-bulb thermometers that give the 

dry-and wet-bulb temperatures, which in turn are used to 

determine relative humidity and dew point.

relative humidity - The ratio, expressed as a percentage of 

the amount of moisture in the air, to the maximum amount 

of moisture the air is capable of holding under the 

same conditions.

residence Time - The time (seconds) required for the fire 

front to pass a stationary point at the surface of the fuel. 

Numerically, it is the flame depth divided by the rate 

of spread.

residual Smoke - Smoke produced by smoldering material 

behind the actively burning fire front.

ring Fire - A fire started by igniting the perimeter of the 

intended burn area so that the ensuing Fire Fronts converge 

toward the center of the block.

rough - The live understory and dead fuels that build up on 

the forest floor over time.

Scorch height (Scorch line) - The average height to which 

foliage has been browned by fire.

Site Prep Burn - A fire set to reduce logging debris 

after clearcutting and control competing vegetation until 

seedlings of the desired species become established (See 

Debris Burning).

Slash - Debris resulting from such natural events as wind, 

fire, or snow breakage, or such human activities as logging 

or road construction.

Smoke Concentration - The weight of combustion products 

(micrograms or cubic meter) found in a given volume of air.

Smoke Management - Application of knowledge of fire 

behavior and meteorological processes to minimize air 

quality degradation during prescribed burning.

Smoke Plume - The gases, smoke, and debris that rise 

slowly from a fire while being carried along the ground 

because the buoyant forces are exceeded by those of the 

ambient surface wind (See Convection Column).

Smoke-Sensitive Area (SSA) - An area in which smoke 

from outside sources is intolerable.

Smoldering Combustion Phase - Combustion associated 

with residual burning of forest fuels behind the fire front. 

Emissions are at least twice that of the fire front, and consist

mainly of tars.

Spot Fire - Fire ignited outside the perimeter of the main 

fire by a fire brand.

Spot Weather Forecast - Special prediction of atmospheric 

conditions at a specific site, sometimes requested by the 

burn boss before igniting a prescribed fire.

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75

Stagnant Conditions - Conditions under which pollutants 

build up faster than the atmosphere can disperse them.

Strip-heading Fire - A series of lines of fire upwind (or 

downslope) of a firebreak or backing fire that will burn with 

the wind toward the firebreak or backing fire.

Ten-hour Timelag Fuels - Dead wood 1⁄4 to 1 inch in 

diameter and, approximately the top 3/4 inch of the 

litter layer.

Timelag - The drying time, under specified conditions, 

required for a dead fuel to lose about 63 percent of the 

difference between its initial moisture content and its 

equilibrium moisture content. Providing conditions remain 

unchanged, a fuel will reach 95 percent of its EMC after 

four timelag periods.

Tractor-Plow - Any tracked vehicle, with a plow for 

exposing mineral soil, with transportation and personnel for 

its operation.

Transport Wind Speed - A measure of the average rate of 

the horizontal movement of air throughout the mixing layer.

Underburning - Prescribed burning under a forest canopy.

Ventilation Factor - An indicator of the lower atmosphere’s 

potential to diffuse and disperse smoke. Numerically, it is 

the product of the mixing height and the transport 

wind speed.

Vertical Fuels - Fuels that provide vertical continuity 

between the ground and tree crowns, thus creating a 

pathway for a surface fire to move into the overstory tree 

crowns, also known as ladder fuels.

Wet-bulb Temperature - Technically, the temperature 

registered by the wet-bulb thermometer of a psychrometer. 

It is the lowest temperature to which air can be cooled by 

evaporating water into it at a constant atmospheric pressure.

Wetline - A line of water, or water and chemical retardant, 

sprayed along the ground and which serves as a temporary 

control line from which to ignite or stop a low-intensity fire.

Wind direction - Compass direction from which the wind 

is blowing.

Wind Profile - A plot of wind speed with height above the 

earth’s surface. 

Windrow - Woody debris that has been piled into a long 

continuous row.
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to restore southern Appalachian pine-hardwood ecosystems: 

effects on mass, carbon, and nutrient pools. Forest Ecology and 

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Wade, dale d.; Johansen, R.W.1986. Effects of fire on southern 

pine: observations and recommendafions. Gen. Tech. Rep. SE-41. 

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NC: U.S. Department of Agriculture Forest Service, Southern 

Research Station. 28 p.

Waldrop, Thomas A. (and others). 1987. Long term studies of 

prescribed burning in loblolly pine forests of the Southeastern 

Coastal Plain. Gen. Tech. Rep. SE-45. Asheville, NC: U.S. 

Department of Agriculture Forest Service, Southeastern Forest 

Experiment Station. 23 p.
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Fire Intensity levels for stand replacement of table mountain pine 

(Pinus pungens Lamb.). Forest Ecology and Management. 

113: 155-166.

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Patrick H. 2006. Research efforts on fuels, fuel models, and fire 

behavior in eastern hardwood forests. In: Dickinson, Matthew B., 

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managers, proceedings of a conference; 2005 November 15-17; 

Columbus, OH. Gen. Tech. Rep. NRS-P-1. Newtown Square, PA: 

U.S. Department of Agriculture Forest Service, Northern Research 

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Waldrop, Thomas A.; Brudnak, Lucy; Rideout-Hanzak, Sandra 

2007. Fuels on disturbed and undisturbed sites in the southern 

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pp. 195-210. 1992 - Elsevier Science.

Waldrop, Thomas A.; Yaussy, Daniel A.; Phillips, Ross J.; 

Hutchinson, Todd A.; Brudnak, Lucy; Boerner, Ralph E.J. 2008. 

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THE RAINBOW SERIES OF WIlDlAND FIRE IN 

ECOSYSTEMS:

Brown, James K.; Smith, Jane Kapler 2000. Wildland fire in 

ecosystems: effects of fire on flora. Gen. Tech. Rep. RMRS-GTR42-vol. 2. Ogden, UT: U.S. Department of Agriculture Forest 

Service, Rocky Mountain Research Station. 257 p.

Neary, daniel G.; Ryan, Kevin C.; DeBano, Leonard F. 2005. 

Wildland fire in ecosystems: effects of fire on soils and water. Gen. 

Tech. Rep. RMRS-GTR-42-vol.4. Ogden, UT: U.S. Department of 

Agriculture Forest Service, Rocky Mountain Research Station. 

250 p.

Sandberg, david V.; Ottmar, Roger D.; Peterson, Janice L. 2002. 

Wildland fire in ecosystems: effects of fire on air. Gen. Tech. 

Rep. RMRS-GTR-42-vol. 5. Ogden, UT: U.S. Department of 

Agriculture Forest Service, Rocky Mountain Research Station. 

79 p.

Smith, Jane Kapler. 2000. Wildland fire in ecosystems: effects of 

fire on fauna. Ogden, UT: U.S. Department of Agriculture Forest 

Service, Rocky Mountain Research Station. 83 p.

Zouhar, Kristin; Smith, Jane Kapler; Sutherland, Steve; Brooks, 

Matthew L. 2008. Wildland fire in ecosystems: fire and nonnative 

invasive plants. Gen. Tech. Rep. RMRS-GTR-42-vol. 6. Ogden, 

UT: U.S. Department of Agriculture Forest Service, Rocky 

Mountain Research Station. 355 p.
Waldrop, Thomas A.; Goodrick, Scott l. 2012. Introduction to prescribed 

fires in Southern ecosystems. Science Update SRS-054. Asheville, NC: U.S. 

Department of Agriculture Forest Service, Southern Research Station. 80 p.

This publication is a guide for resource managers on planning and 

excecuting prescribed burns in Southern forests and grasslands. 

It includes explanations of reasons for prescribed burning, environmental 

effects, weather, and techniques as well as general information on 

prescribed burning.

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