ECOLOGY OF FIRE IN GRASSLANDS
231
bacteria. The bac*tcria in turn decompose more organic matter and this
rerlults in ti liberation of available N.
'I'hc extent to which these heat influences operate in grassland burning is probably negligible. If soil temperature during a fire is raised
only a fraction of a degree at a depth of 2 cm, it would seem that fire
can scarcely have significant direct effects on the soil biota (Heyward,
1938; Vareschi, 1962). Yet it cannot be denied that fire commonly increases plant vigor and vitality in such a way as to suggest marked
increases in fertility. The role of microorganisms in this problem deserves far more attention than it has been accorded.
Meiklejohn (1955) studied the microflora of the top 25 mm of soil for
5 months following burning experiments in Kenya. One of her plots
supported Acacia with a grass cover beneath and so is pertinent here.
The total number of organisms in the microflora was decreased in consequence of the fire, with this effect persisting for at least 3 months.
Burning completely eliminated fungi (acaording to plate counts) but
populations were back to normal 2 months later, with PeniciUium still
dominant ac: before. Actinomyces and bacteria were reduced in numbers
and still had not recovered 3 months after the fire when the last analysis
was made. Anaerobic N fixers (Clostridium), though poorly represented,
persisted through the burning. When sampled 11 weeks after, and
again 5 months aftcr the fire, total N was higher, probably as a result
of destroying the nitrifiers which would otherwiee have converted much
N into soluble forms which could leach deeper. Cohen (1950) compared
grassland plots in Kenya one of which had been regularly burned, and
the other protected, neither plot had been grazed. Burning produced a
richer fungus flora, but one less actively spore-producing.
Regular burning of grass cover beneath pines on the Coastal Plain
of southeastern North America incremes humus and total N of the soil
and also doubles the bacterial count (Greene, 1935a), but the animal
life in these soils is affected adversely, The micro- and macrofauna in
the upper 60 m m of the mineral soil in unburned areas is only 11 times
as dense as in burned sites, although qualitatively there is little difference (Heyward and Tissot, 1936). Fire-induced reduction in the
porosity of these soils was attributed to this faunal impoverishment.
In Illinois fire reduced the populations of most forms of animal life
in a grassland tract, but did not reduce the ant populations (Rice, 1932).
H. A B O V E - G R O U N D ANIMALS
1. Birds
Fire can be devastating to ground-nesting birds. It not only destroys
existing nests but removes the protective cover necessary for constructing new ones, and eliminates insect food resources (Bird, 1930; Bowen,
231
bacteria. The bac*tcria in turn decompose more organic matter and this
rerlults in ti liberation of available N.
'I'hc extent to which these heat influences operate in grassland burning is probably negligible. If soil temperature during a fire is raised
only a fraction of a degree at a depth of 2 cm, it would seem that fire
can scarcely have significant direct effects on the soil biota (Heyward,
1938; Vareschi, 1962). Yet it cannot be denied that fire commonly increases plant vigor and vitality in such a way as to suggest marked
increases in fertility. The role of microorganisms in this problem deserves far more attention than it has been accorded.
Meiklejohn (1955) studied the microflora of the top 25 mm of soil for
5 months following burning experiments in Kenya. One of her plots
supported Acacia with a grass cover beneath and so is pertinent here.
The total number of organisms in the microflora was decreased in consequence of the fire, with this effect persisting for at least 3 months.
Burning completely eliminated fungi (acaording to plate counts) but
populations were back to normal 2 months later, with PeniciUium still
dominant ac: before. Actinomyces and bacteria were reduced in numbers
and still had not recovered 3 months after the fire when the last analysis
was made. Anaerobic N fixers (Clostridium), though poorly represented,
persisted through the burning. When sampled 11 weeks after, and
again 5 months aftcr the fire, total N was higher, probably as a result
of destroying the nitrifiers which would otherwiee have converted much
N into soluble forms which could leach deeper. Cohen (1950) compared
grassland plots in Kenya one of which had been regularly burned, and
the other protected, neither plot had been grazed. Burning produced a
richer fungus flora, but one less actively spore-producing.
Regular burning of grass cover beneath pines on the Coastal Plain
of southeastern North America incremes humus and total N of the soil
and also doubles the bacterial count (Greene, 1935a), but the animal
life in these soils is affected adversely, The micro- and macrofauna in
the upper 60 m m of the mineral soil in unburned areas is only 11 times
as dense as in burned sites, although qualitatively there is little difference (Heyward and Tissot, 1936). Fire-induced reduction in the
porosity of these soils was attributed to this faunal impoverishment.
In Illinois fire reduced the populations of most forms of animal life
in a grassland tract, but did not reduce the ant populations (Rice, 1932).
H. A B O V E - G R O U N D ANIMALS
1. Birds
Fire can be devastating to ground-nesting birds. It not only destroys
existing nests but removes the protective cover necessary for constructing new ones, and eliminates insect food resources (Bird, 1930; Bowen,