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FUEL
TYPE
MAPPING
IN REGION
ONE
BY L. G. HORNBY
NorthernRocky MountainForestand RangeExperimentStation
The mappingof a fuel is simply the identificationof the place where a specifickind
of fire behaviorand difficulty,or expense,of control are expected. The article presents,in abbreviatedform, instructionsissued to fuel mappers in northern Idzho and
western Montana. Under this method, which was developedincidental to fire control
and transportation planning, fifteen million acres of national forest fuels have
been mapped to date.
Ratingswill assumeconditionsafter a
HE reason
formaking
a fuelmap month
of continuous mid-summer drouth
is to know,beforea fire occurs,
under a given degree of weather
danger,what speedand strengthof attack will be required.
The rate at which a fire will spread
determineshow many chainsof fire line
will be producedper hour. The difficulty of firefightingcausedby slopeand
soil, togetherwith amount,size, arrangement and speciesof fuel along the peri-
has prevailed.
Consideration
will
be limited
to
the
first few hoursafter a fire is largeenough
to be discoverable,i.e., to the elapsed
time requiredfor travel and firefighting.
The scale one inch to the mile will
be
standardfor presentfield mapping. For
planningpurposesfield mapswill be reduced to half-inch
scale.
This methodomits a detailedinventory
meter of the fire, determineshow many
man-hoursof work will be required for on the assumptionthat the best conclu-
each chain of fire line. Evidently the
man-hoursper chain multiplied by the
numberof chainsto be workedgivesthe
firefightingjob to be done. Fuel maps
will show,accordingto the mappinglegend, the probablerate o! spreadand the
resistance to control.
sions can be drawn by men looking at
the amount,arrangementand continuity
of fine fuels and their exposureto sun
and wind. It is adaptedto refinementas
usable data on combined influences be-
come available. It statesconciselywhat
plannersand dispatchers
need to know.
Fine fuels consist of such materials as
branches of •trees less than one inch in
The first use of this map will be in
makingpreparations
for firesthat may occur, stationingfiremenfor detection,and
stationingone or severalof them within
permissibletravel-timedistancesas necessitated by fuels. The most frequentuse
will be by dispatcherssendingmen to
diameter,shrubsand herbaceousplants,
loose,rotten wood and bark, frayed, broken trunks,open rottenchecks,mossand
deadneedleson snagsand windfalls,and
needles,leaves, duff, weeds,grass and
fires.
moss on the forest floor.
Firemen and their expensiveimprovements,includingroads,mustbe locatedin
relation
to fuels
and cannot
RATE OF SPREAD
be moved
Four classes
are recognized.The mapannually. Mappersare expectedto rate
fuels as they will be five years after per should endeavorto visualizeall the
examination.
Estimates of such known
different rates of spread that have occhanges
as resultfrom burns,blowdowns, curred. He should divide these into three
epidemicsand cutting operationsare re- equalpartscalledlow, medium,andhigh,
and assigneach fuel he encountersto
quired.
67
JOURNAL OF FORESTRY
68
TAR•
DIFFERENCES
IN
MOISTURE
OF
1
VARYING
per
cent
moisture
•
Clear-cut area ....
Half-cut area.......
Full-timberedarea
IN
STANDS
DENSITY
At 9:00 A.M.
Timberdensity
ment to have no rain
CONDITIONS
5.3
6.0
8.7
At 4:30 P.M.
contents
per cent
2.4
4.4
6.1
and to be in mid-
fire-season
of a disastrousyear. Extreme
burning conditionshad beendemonstrated
on oppositesidesof this set of weather
instruments.For any factor sevendaily
recordswere averagedfor each hour of
the day to obtain a representativeday.
It was found
that between 7:00
A.M.
•Moistureis in percentage
of oven dry to 4:30 P.M. temperaturewas high and
weight of cylinders.
humidity low, accordingto opennessof
oneof theseclasses.
A fourthclass,ex.
the stand.
treme,hasbeenspecified.It is considered Half-inch wood cylinders,ten inches
an exclusive
part of the highestclassre- above ground, showedthe record given
servedfor the worstpartsof blowdowns,in
cut-over areas and single burns. Grass
is eliminated.
Where large fires are observedto have
stopped
naturally,the influences
of precipitation,
highhumidity,changeof wind
andnightcooling,workingsinglyor in
combination,
have frequentlybeen the
cause rather than the fuel.
Reliable guidesto probablerate of
spread are available in consistentdata
collectedat widely separatedforest experiment stations.
Table
1.
Wind influences
rate of spreadin two
very differentways. In placesexposedto
dry, prevailing winds, fuels are being
dried and prepared for more rapid
spread than in shelteredplaces. After
ignition,wind increases
the rate of spread
by supplying oxygen for combustion.
Varying with the steepness
of slope, rising hot air currentspreparefuels up the
slopeaheadof a fire for rapid combustion,
while the cooler air, comingin below,
provides oxygen.
It will
be noted that tree crowns and
EFFECT OF DENSITY OF CANOPY
trunkscut the afternoonwind velocityof
the open down to about one-twentiethin
At PriestRiver,NorthernRockyMoun- the full-timber,at nine feet aboveground.
tain ExperimentStation, U.S.F.S.--H. T. Undoubtedly
the wind wasmovingas fast
Gisborne has established three weather
above the tree crowns as it was at the
stationsabout 500 feet apart in a line clear-cut station, and fine dead fuels in
approximatelyparallel to the prevailing the crowns would exhibit the same tendenwind direction. All are on a flat that
cies toward fast spreadexceptthat evaporiginallybore a densestandof over- oration would modify it. Small changes
mature white pine-hemlocktype. The in humidity exert a much greater influwind and sun have full accessto the station farthest south, where the timber was
clear-cut. Northward, with the wind, the
TABLE
2
next station is in timber whosecanopy
was half-cut.
Around the third station the
natural forest was untouched.It is protected from wind by about 500 feet of
half-cutplus 300 feet of virgintimber.
The week August 10-16, 1931, was
selectedfor study of differencesat these
stations becauseit satisfiedthe require-
THE
AVERAGE
DAILY
RECORD
OF
WIND
AT
GISBORNE'S THREE WEATHER STATIONS.
Wind in miles per hour, average
From 5:00 P.M.
From 9:00 A.M.
to 9:00 A.M.
to 5:00 P.M.
Timber density
Clear.cut
area ......
1.2
3.8
Half-cut area ........
Full-timbered area
0.6
0.1
2.3
0.2
FUEL TYPE MAPPING
IN REGION
ONE
69
enceon inflammabilitythan small changes only scattered
treesof ponderosa
pine are
able to exist.
in temperature.
At Northeast Forest Experiment StaThe extremetop portion of the south
tion, U.S.F.S.--Data from Massachusetts exposure,where Douglasfir is invading
were publishedby Paul W. Stickelin ponderosapine, showsalmost as thorPulp and Paperin Canada,January,1933. ough drying of the surfacesoil as any
Comparisons
of inflammabilitywere pre- otherportion,but appreciablylowertemsentedfor four degreesof thinning. The peratures.
conclusionsagree with the data from
North exposure.--"From the bottom
Priest River.
of the valley to almostthe top of the
north exposurerelatively moderatetemEFFECT OF TOPOGRAPHIC SHELTER
peraturesare experienced,
both on account
of
the
angle
of
incidence
of
the sun'srays
In Region1 the prevailingwind direcand the completeness
of the cover. On
tion is from southwest to northeast and
only rarely are fires or fuels influenced the lowestand also steepestportion,the
by generalwinds moving in any other evaporationrate is lowest,the soil temperatures are lowest, the accumulation
direction.
of
moistureis greatest,and the drying of
Shade is simply absenceof sunlight.
the soil is mostgradual. So far as these
Whatever causes it reduces the amount of
are the resultsof steepslope, the con&radiation received from the sun.
Obviously,slopesbombardedall day tions would probably exist in a degree
and tilted so as to be perpendicularto
thesunat its highestmiddaypositionwill
receivethe greatestpossiblyquantity of
solar radiation.
EFFECTS OF COVER AND TOPOGRAPHY
if all cover were removed."
Spruce,almostpure, occupiesthe lower part of the north exposure.
"The upper portion becomesprogressively warmer and drier. Here, evidently, are encounteredabout the mean temperature conditionswhich are favorable
.4t FremontExperimentStation,U.S.F.S., to Douglasfir. But it shouldbe notedon
once the Douglas
Colorado.-•The following informationis all similar exposures,
obtained from Carlos G. Bates' article
fir forest is established,there is a marked
"The Transect of a Mountain Valley," tendencyfor Engelmannspruce to inEcology,January,1923.
vade and supersedefir."
For fuel mappersthe importantcontributionis a correlationof speciesas well
TABLE 3
as densityof standswith the inflammaFIRES JUNE 21-SEPT. 10 OF 1926 AND 1929 COMbility factors,temperature,moistureand BINED. ORIGINS IN UNCUT GREEN FORESTS• ATexposure.The topographyinvolved is a
TACKED 0-24 HOURS AFTER IGNITION.
valley 700 feet wide with axis east-west.
South exposure.--"All of the southexposureis subjectedto direct insolationat
sometime duringthe day and during the
entire year. As a result, high maximum
temperatures
(150ø F.) are recordedat the
surface of the soil (60 ø above the cool-
estneighboringsite)."
Near the foot of the south exposure
NE •
SW •
397
414
7.1
7.0
0.52
0.62
leach direction includes a half circle.
0.07
0.09
70
JOURNAL OF FORESTRY
FIRE IN RELATIONTO FUEL TYPE
The evidenceseemsto permit the conclusionthat any densityof stand,by obGreen Stands, Uncut, Pole Size and
structingwind and sun, makespossiblea
Larger.--From
an exhaustive
study of
greaterdensity,accompanied
by reduction
rates of spreadthat occurred1921-30,it
of inflammability, until a climax is
wasfoundthat the standardtypeslined
reached.
up in the followingdescending
order:
1. Brush-grass
Fuel mappersare warned againstthe
2. Ponderosapine
assumptionthat all north exposuresare
moist and cold.
West of north-south
3. Lurch-fir
di-
vides they are dried more by wind than
east of those divides. At junctions of
valleys north slope vegetationfrequently
is typical of moderatelydry sites.
As the drouth of fire season continues
4. Douglasfir and lodgepole
pine
5. White pine and cedar-hemlock
6. Subalpine
7. White fir and spruce
This order is approximately
the same
as density of stand and is consistentwith
the moisture contentsof protectedand Bates' data from Colorado. The same
exposedfuels becomemore alike. How- relativeorder was found for any severever, analysis of fires' that occurred in ity in burningconditions.
mid-seasonof the two worst years out of
Unfortunately,
the merepresence
of a
ten shows that differences still exist.
particulartimbertypedoesnot determine
TASLE 4
EXAMPLE
OF FIRr.
Example
no.
1
2
SPRr.AD AND
RESISTANCE
RATINGS
FOR
VARIOUS
KINDS
OF
FUr. L
Description of fuel
E--extreme, H----high,M----medium,L----low
Ponderosa pine, mature stands on SW slopes
with reproduction scattered or absent....................
With reproduction moderately dense.....................
Spruce, white fir or cedar-hemlock mature, norreally dense in protected bottoms. If rough
Rateof spread
Resistance
to control
H
H
L
M
L
H
L
L
snags are conspicuouslypresent and green trees
are limby, connecting fuels on ground to mossy
3
4
5
6
crowns
....................................................................
If snags are smooth and thinly scattered while
green trees are clean of mossand brushy limbs_..
White pine, lurch-fir, Douglas fir or lodgepole
pine, normally dense stands, windfall and snags
almost absent, ground vegetation conspicuously
low shrubs; on protected flats and NE exposures
On exposed flats and gentle SW exposures
with usual increasedopennessand prevalenceof
grass, with snags and windfall moderate but
not
continuous ...................................................
L
M
M
Any species except ponderosa pine; mature
dense stands, 80 per cent q- killed by ground
fire or epidemic, leaving all dead foliage on
trees;
half
or more of dead trees down and
not completelyshadedby reproduction. On ex7
8
posed SW slopes.....................................................
On protected NE slopes.....................................
If same stands burned hot enough to consume
E
H
9
10
fine fuels. On exposedSW slopes......................
On protected NE slopes......................................
H
M
H
tl
FUEL TYPE MAPPING IN REGION ONE
the probablerate of fire spreador re-
71
RESISTANCETO CONTROL
sistanceto control at a specificspot. It
simplyindicatesthe degreeto whichpart
Resistance
to controlis the intensity
of the influencesare present. The age of firefighting
difficulty.It is the amount
of a stand, in combination with the
of workperchain,or otherunit,of peri-
amountand conditionof older or young- meter length.
er intermixeddeadand greentrees,means Thedegrees
of resistance
to bemapped
much.
are designated
in the sameterms as used
Burns, Cut-over Areas, Blowdowns, for rates of spread--low,medium,and
Snags, Moss.--As burns produce open- high--with a fourthclass,extreme,to be
nessof stand it might be expectedthat usedfor conspicuously
difficultfuels.
ratesof spreadtherewouldbe fasterthan
The importantfactors that determine
in greentimber of the sametype. This resistance are:
tendencywas only slightly exhibitedby
the 1,536 fires recordedas originating Fuelconditions Existingin
there. The condition commonlycalled
Standinggreentimber
burn has included large areas of brush Amount
and reproductionup to 30 years old. Arrangement
Snags
This growthis performingthe samefunc- Size
Windfall and slash
tions of shelter as mature
stands to the
Species
degreethat fine fuels are being shaded
and air movement
aroundthemprevented. Decay
Between burned areas and unburned clear-
Brush,reproduction
and grass
Duff and roots
cut areas,bare groundis frequentin the
former
and rare
in the latter.
TRENCHINGAND DIRT-SMOTHERING
Cutting operations,in general, have
CHANCE
produceda high degreeof opennessin
stands.It was foundthat ratesof spread
Roots, soil, rocks, slopes.--Thefuel
conformedmore to a completeness
of
mapper
will assumethe method of atslashdisposalthan to timber type. Un-
tackto be by ordinaryhandwork,using
the
mostsuitabletools. In ratingresisspreadweremuchfasterin cut-overareas
der all severities of weather, rates of
than in uncut,green forestsor in single tance,he is to judge only the work reburns.
quired to corral fires and to hold them
the middayburningperiod.He
The completeblowdownof a dense through
should endeavor to visualize an efficient
stand, fully exposedto sun and wind,
mustbe giventhe highestpossiblerating. fireman,doingwhateverwork existsat the
spot under consideration.
Initial ignitions are not likely to
spread aerially betweensnagsthat are
RATINGSFOR TYPICAL R-1 CONDITIONS
morethan 75 feet apart. Examination
of
the fuel on the ground at the foot of
snagsand betweenthem is necessaryto
At five trainingcampsfor fuel mapknown the probability of fire running pers 90 men, representing10 national
there.
forests,agreedon 42 ratingsto be asFuel mapperswill recognizemossonly signedto typicalfuelsof Region1. From
in conjunctionwith other fuels. The most themthe examples
in Table4 are given
importantassociation
is with loose,dead as guidesto the reasonsfor increasing
bark and dead crowns.
ratings as fuel dangersincrease.
72
JOURNAL OF FORESTRY
The productionof a map, showingthe
Anothernecessitysatisfiedby the fuel
locationof eachclassof fuel, is simply' map is in makingtotal dangerratings
a step toward providing protectionproportional to the need for it. Analysis
has shownwhat ratesof spreadto expect
and what progressdifferent numbersof
men can make.
From this information
an
for
forest areas that differ
in the three
essentialconsiderations,
fuel danger,values at stakeand frequencyof occurrence.
By addingtogetherthe dangersof small
areas the total amount coveredby different detectors,smokechasers,roads and
allowable travel time has been derived for
trails, per dollar of annual expensehas
each fuel
been determined.
class.
"The independent
effortof an individualmay be but a feeblegesture....
But whenhe joins in massformationwith his neighbors
the sameeffort becomes
an irresistibleand mighty force. CornellJanCouncilBulletin, Oct., 1934.