K(Y)l,o(; Y OF FIRIS IS ORASSL4SL~Y
429
h i ~ v t ! f c i i r n d N ( w i d i t . i ~ ) x ~ ~
cic:finitaly improved in coi~s~.!qi~cncc of grass
firc:x. I n c1c~ivc:ti HiiviLririit of Xigcriit, X W ~ L H I c t \ w t i t in 1)lc)ts protected
from burning (Moore, IMO). On the (,k)iistal i'lain of.qouthe;~,qtern Korth
Arxicricn frequent burnirg of savaxina grass raises t.hc total X of the
upper l&-i,G cmi of t.he soil profile ((iarren: 19-13: Grecnct. 1!)35a; Hey\Pard
and Barnr?t,tt,, 1934). Also, burning of the H~utt2074,o st.eppe of nouthcnst.ern Arizoiin usually incrtbitsw t h S contmt of the upper 25 mm
of the soil, evm though it has no consistent effect' on the total organic
mtitter (Meynolds and Lbhning, l!+X). .Hurt.on (1 944) made the significant ot)scrvat.ion t.httt the iidditiw of any fertilizer cont.aining S hsd
t.he same cf5c:t in stimiiinting the ihwering of grasses ,is does hurliiikg.
In South -4frica pioneer grasses arp favoured by N cithcr a s ammonium
or nit,rate, whereas species characteristic of later successional sages itre
intolerant of high Pi (Jonp and ILoux, 1956); so some of tho changes lu
species composition after grass burning may be a cci~~si~quence of
changed h' st-
heat.ing of soils as a conseyuencc of readjust,ments in microbial populations that favor t,he bacterial decomposition of humus. Often it is
hypothi?cated thitt the invigorated nit,rificlition following fire is an egect
of the generally raised pH, for t.his response is usudly obtained by a
rediwtion of acidity in the substrate of bacteria. Hut, this seem8 not to
hold for nitrification. The optimal temperature for nitrification and its
u+ke by plants are rclat ively high (c. 35-45"C). whereas under exprrirnctntal conditions at, least, nitxification is relatively insensitivc to pW.
So it is morc likely that the iiic.reasc?d nit,rification nftw fire is a response
to higher ternpcriitiire Irwl in soil exposod directly to the sun ritther
tlirtn to raised p H (Klitck, 1!457).
At least, pmt, of tht: N increase t>hiit has been observed in burned
savannas in southea&ern Xort,h America is a consequenc,e of firat,ion
by legwries t,hitt, increase miirkedly following gr+s fires (Garren, 1943).
After 8 years of annunl burning the total N was increased by 50";
in t.he upper 15 cm of the prolile, this chttnge was attributed in part to
legume incwiises, in part to the decay of root.8 of the fire-sensitive
species that were killed, and in part, to the increased produc.tivity and
turn-over rate (Qrcent:, 1935). Likewise in African savnnxla (Lemon,
1964)1 and in arinual g r a d a n d in California (McKc>li et d., lgti?),
legumes have h e n obscrved tjo increase following fire. It is possible
that this phenomenon reflects n i i adapt ivc responst? of these p:irtiaulttr
leguminous species to rin environment, frequently subjected to fire, for
tho seeds of' It*gurnc?s used as vep>tablr and field crops itre relat,ivcly
sensit,ive t,o I l ~ ~ i t t .
injury (Cuwiw, I M G ) .
Kucera s1id 1StIrtwrc~ic.h ( 1 ! ~ i 2 ) suggexwd t8hatJ the rcniovai of Iargc.
429
h i ~ v t ! f c i i r n d N ( w i d i t . i ~ ) x ~ ~
cic:finitaly improved in coi~s~.!qi~cncc of grass
firc:x. I n c1c~ivc:ti HiiviLririit of Xigcriit, X W ~ L H I c t \ w t i t in 1)lc)ts protected
from burning (Moore, IMO). On the (,k)iistal i'lain of.qouthe;~,qtern Korth
Arxicricn frequent burnirg of savaxina grass raises t.hc total X of the
upper l&-i,G cmi of t.he soil profile ((iarren: 19-13: Grecnct. 1!)35a; Hey\Pard
and Barnr?t,tt,, 1934). Also, burning of the H~utt2074,o st.eppe of nouthcnst.ern Arizoiin usually incrtbitsw t h S contmt of the upper 25 mm
of the soil, evm though it has no consistent effect' on the total organic
mtitter (Meynolds and Lbhning, l!+X). .Hurt.on (1 944) made the significant ot)scrvat.ion t.httt the iidditiw of any fertilizer cont.aining S hsd
t.he same cf5c:t in stimiiinting the ihwering of grasses ,is does hurliiikg.
In South -4frica pioneer grasses arp favoured by N cithcr a s ammonium
or nit,rate, whereas species characteristic of later successional sages itre
intolerant of high Pi (Jonp and ILoux, 1956); so some of tho changes lu
species composition after grass burning may be a cci~~si~quence of
changed h' st-
heat.ing of soils as a conseyuencc of readjust,ments in microbial populations that favor t,he bacterial decomposition of humus. Often it is
hypothi?cated thitt the invigorated nit,rificlition following fire is an egect
of the generally raised pH, for t.his response is usudly obtained by a
rediwtion of acidity in the substrate of bacteria. Hut, this seem8 not to
hold for nitrification. The optimal temperature for nitrification and its
u+ke by plants are rclat ively high (c. 35-45"C). whereas under exprrirnctntal conditions at, least, nitxification is relatively insensitivc to pW.
So it is morc likely that the iiic.reasc?d nit,rification nftw fire is a response
to higher ternpcriitiire Irwl in soil exposod directly to the sun ritther
tlirtn to raised p H (Klitck, 1!457).
At least, pmt, of tht: N increase t>hiit has been observed in burned
savannas in southea&ern Xort,h America is a consequenc,e of firat,ion
by legwries t,hitt, increase miirkedly following gr+s fires (Garren, 1943).
After 8 years of annunl burning the total N was increased by 50";
in t.he upper 15 cm of the prolile, this chttnge was attributed in part to
legume incwiises, in part to the decay of root.8 of the fire-sensitive
species that were killed, and in part, to the increased produc.tivity and
turn-over rate (Qrcent:, 1935). Likewise in African savnnxla (Lemon,
1964)1 and in arinual g r a d a n d in California (McKc>li et d., lgti?),
legumes have h e n obscrved tjo increase following fire. It is possible
that this phenomenon reflects n i i adapt ivc responst? of these p:irtiaulttr
leguminous species to rin environment, frequently subjected to fire, for
tho seeds of' It*gurnc?s used as vep>tablr and field crops itre relat,ivcly
sensit,ive t,o I l ~ ~ i t t .
injury (Cuwiw, I M G ) .
Kucera s1id 1StIrtwrc~ic.h ( 1 ! ~ i 2 ) suggexwd t8hatJ the rcniovai of Iargc.