l.;COLOQY OF FIRE IN GRASSLANDS
315
microt.lirn;it ic factors that determine the init.ial temperature of the
(‘or11 tjust i l j i c b ni:it,c-rial a ~ ~ l
moist urc conditions.
(8) ‘I’tit, kirrtl, itK1oilrit and disposition of fuel that hiis accumulated
Hint:;? t tic! 1:tst fin: is : L third irnport;int. fact.or (Hopkins et al., 1948). In
Orcgon wlic~i~o gr;iziiig I d prevuiitcd t h o accumulation of a he:ivy litter,
the reduced tlil.mugc of a grass fire, in comparison wit.h a contiguous
ungrazed arm, providvd indirect, evidence suggesting that less fuel
resuIt,ctl in a loww level of 1ieat.ing (Conrad and Poulton, 1966). Iwanami
a,nd lizrrrni (1!)66a) huriied areas which tticy covered with 0-2, 0-4, 0.8
and 1 .:! kg of dry ~liwnn1hu.s sinensics litter per square metre, recording
temperatilrcs with t,hermocoiiples at elevations of 3, 5, 8, 11, 14 cm,
up t>o 200 cm. The grent.er the litter cover the higher t.he maximum
temperature they recorded. According to McArthur (1963) with each
doubling of fuel quantity per unit, area t,he rate of fire spread, flame
height, mid fir between the level to which the soil was heated and the quantity of fuel
consumed. This probably refiects no more than t,he complexity of intera.ctiiig variables whcre exprriniciital condit
I‘enezuelan montane ~av;inna I’tPridium mudaturn, which invades
burned areas twnpornrily, ha8 a higher burning tem perature than the
p a s s cover it repitwes (Varcwchi, I W ? ) .
The elevation nf t h~ mttximum tempcmkure attained differs between
backfires and hcdfirc*s. When gritss pliw pine needles burn on the
Atlantic (hast,al Plain of southeasIern North America, the altitude of
the maximum temperat.me of headfires average8 4 dm, whereas the
maximum in bapkfires averages only 1 dm above the ground (Byram,
1958; Heywartl, 1938). During a hendfirct (there referred to a,s “under a
headwind”) started att 14.30 h with a wind velocity of 0.5 m/sec,
Iwanami and Iizumi (1!)61fi:i) recorded a maximum temperature of
570Y1, at an altitudc of .8 em. In a hackfire (“under R back wind“)
st,:irtcd a t 15.40 h with tht. same wind velocity, a maximum of 877°C
was obtsinetl at 8 cm. Thus in those conditions the elevation of the
maxirnal ternperatures was equal, hilt the backfire was the hotter.
Byram (1958) suggefits t.hat the higher altitude of the temperature
maximum in hoadfires which he studind may result from t,hese fires
ignii.iiig crtct plant, shoots first a t their distal ends so that( much of t,he
eornbunt.ion takca place well above t,he ground before flames follow the
shoots doxii to t,heir hnsca. Also the more rapid spread of the blaze
results in more fiicl burning a t any one time. On the other hend, a backfire spreads near thc ground, so the bases of shoots burn through quickly
315
microt.lirn;it ic factors that determine the init.ial temperature of the
(‘or11 tjust i l j i c b ni:it,c-rial a ~ ~ l
moist urc conditions.
(8) ‘I’tit, kirrtl, itK1oilrit and disposition of fuel that hiis accumulated
Hint:;? t tic! 1:tst fin: is : L third irnport;int. fact.or (Hopkins et al., 1948). In
Orcgon wlic~i~o gr;iziiig I d prevuiitcd t h o accumulation of a he:ivy litter,
the reduced tlil.mugc of a grass fire, in comparison wit.h a contiguous
ungrazed arm, providvd indirect, evidence suggesting that less fuel
resuIt,ctl in a loww level of 1ieat.ing (Conrad and Poulton, 1966). Iwanami
a,nd lizrrrni (1!)66a) huriied areas which tticy covered with 0-2, 0-4, 0.8
and 1 .:! kg of dry ~liwnn1hu.s sinensics litter per square metre, recording
temperatilrcs with t,hermocoiiples at elevations of 3, 5, 8, 11, 14 cm,
up t>o 200 cm. The grent.er the litter cover the higher t.he maximum
temperature they recorded. According to McArthur (1963) with each
doubling of fuel quantity per unit, area t,he rate of fire spread, flame
height, mid fir between the level to which the soil was heated and the quantity of fuel
consumed. This probably refiects no more than t,he complexity of intera.ctiiig variables whcre exprriniciital condit
I‘enezuelan montane ~av;inna I’tPridium mudaturn, which invades
burned areas twnpornrily, ha8 a higher burning tem perature than the
p a s s cover it repitwes (Varcwchi, I W ? ) .
The elevation nf t h~ mttximum tempcmkure attained differs between
backfires and hcdfirc*s. When gritss pliw pine needles burn on the
Atlantic (hast,al Plain of southeasIern North America, the altitude of
the maximum temperat.me of headfires average8 4 dm, whereas the
maximum in bapkfires averages only 1 dm above the ground (Byram,
1958; Heywartl, 1938). During a hendfirct (there referred to a,s “under a
headwind”) started att 14.30 h with a wind velocity of 0.5 m/sec,
Iwanami and Iizumi (1!)61fi:i) recorded a maximum temperature of
570Y1, at an altitudc of .8 em. In a hackfire (“under R back wind“)
st,:irtcd a t 15.40 h with tht. same wind velocity, a maximum of 877°C
was obtsinetl at 8 cm. Thus in those conditions the elevation of the
maxirnal ternperatures was equal, hilt the backfire was the hotter.
Byram (1958) suggefits t.hat the higher altitude of the temperature
maximum in hoadfires which he studind may result from t,hese fires
ignii.iiig crtct plant, shoots first a t their distal ends so that( much of t,he
eornbunt.ion takca place well above t,he ground before flames follow the
shoots doxii to t,heir hnsca. Also the more rapid spread of the blaze
results in more fiicl burning a t any one time. On the other hend, a backfire spreads near thc ground, so the bases of shoots burn through quickly