IZCOLOOY OF FIRE IX GRASSLANDS
221
In grassy openings in Wisconsin fore&, where southerly exposure
and thin soil conspire to provide conditions probably drier than in the
sites referred to above, litter cover at the end of the first post-burn
season was only 26% of that on unburned areas, and it waa estimated
that 5 years would be required for a return to normalcy. Even drier is
the steppe site in central Kansas where studies showed that grass shoots
require approximately four years to become finely granular and ready
to enter the mineral soil (Hopkins, 1954).
Moving to the pine savannas along the Coastal Plain in Louisiana
where unburned areas supported 5604 kg litter/hectare, 64% had
accumulated again a t the end of the first post-burn season (Duvall,
1962). In Georgia litter cover ww back to normal 5 years after a fire in
grassy pine woods (Lemon, 1949).
The information at hand, all of it obtained in the eastern U.S.A.,
shows that 2-6 years are required for a normal litter cover to accumulate following the firing of grassland, with variations in the rate of
accretion not bearing a clear relation to climate.
2. Humus
Frequent burning of the grass beneath pines in the Coastal Plain of
southeastern North Anicrica has been shown to increase the organic
matter content of the upper 10-15 cm of the soil profile (Greene, 1935a;
Heyward, 1936; Heyward and Barnette, 1934; Wahlenberg et al., 1939).
In Mississippi this amounted to a600/, increase (Greene, 19358). Shantz
( 1947) opined that these reported increases represent mainly charcoal
fragments, rather than humus, pointing out, as Wahlenberg et al. (1939)
had earlier Iemarked, that the loss-on-ignition method used in soil
analyses did not distinguish between these forms of organic matter.
However, the low levels of soil heating that have been recorded in relation to the high levels of temperature required to char plant tissue in
the soil (Heyward, 1938) suggest that any charcoal dispersed through
the soil protile would have to be the small amount that could be
mechanically incorporated, rather than being formed in place. More
convincing are the comparative analyses by Metz et al. (1961), showing
that although loss-on-ignition does give exaggerated values as an estimate of humus content, wet-combustion analyses still reveal an increase
in humus in frequently burned parts of these Coastal Plain soils. In
Britain even a single burn was reported to have resulted in an increasc
in humus (Eden, 1924).
In an early report (Aldons, 1934) on the results of 6 years of annual
burning of Andropogon scoparius steppe in eastern Kansas, humus content had not declined in the upper 15 om of the profile, regardless of the
season of burning. But a later report on a continuation of the project
221
In grassy openings in Wisconsin fore&, where southerly exposure
and thin soil conspire to provide conditions probably drier than in the
sites referred to above, litter cover at the end of the first post-burn
season was only 26% of that on unburned areas, and it waa estimated
that 5 years would be required for a return to normalcy. Even drier is
the steppe site in central Kansas where studies showed that grass shoots
require approximately four years to become finely granular and ready
to enter the mineral soil (Hopkins, 1954).
Moving to the pine savannas along the Coastal Plain in Louisiana
where unburned areas supported 5604 kg litter/hectare, 64% had
accumulated again a t the end of the first post-burn season (Duvall,
1962). In Georgia litter cover ww back to normal 5 years after a fire in
grassy pine woods (Lemon, 1949).
The information at hand, all of it obtained in the eastern U.S.A.,
shows that 2-6 years are required for a normal litter cover to accumulate following the firing of grassland, with variations in the rate of
accretion not bearing a clear relation to climate.
2. Humus
Frequent burning of the grass beneath pines in the Coastal Plain of
southeastern North Anicrica has been shown to increase the organic
matter content of the upper 10-15 cm of the soil profile (Greene, 1935a;
Heyward, 1936; Heyward and Barnette, 1934; Wahlenberg et al., 1939).
In Mississippi this amounted to a600/, increase (Greene, 19358). Shantz
( 1947) opined that these reported increases represent mainly charcoal
fragments, rather than humus, pointing out, as Wahlenberg et al. (1939)
had earlier Iemarked, that the loss-on-ignition method used in soil
analyses did not distinguish between these forms of organic matter.
However, the low levels of soil heating that have been recorded in relation to the high levels of temperature required to char plant tissue in
the soil (Heyward, 1938) suggest that any charcoal dispersed through
the soil protile would have to be the small amount that could be
mechanically incorporated, rather than being formed in place. More
convincing are the comparative analyses by Metz et al. (1961), showing
that although loss-on-ignition does give exaggerated values as an estimate of humus content, wet-combustion analyses still reveal an increase
in humus in frequently burned parts of these Coastal Plain soils. In
Britain even a single burn was reported to have resulted in an increasc
in humus (Eden, 1924).
In an early report (Aldons, 1934) on the results of 6 years of annual
burning of Andropogon scoparius steppe in eastern Kansas, humus content had not declined in the upper 15 om of the profile, regardless of the
season of burning. But a later report on a continuation of the project