ECOLOGY OF FIRE IN GRASSLANDS
225
changing fine crumb structure to single-grained or massive. These
changes do not alter the moisture-retaining capacity of the soil, but its
moisture content is lowered on the burned areas to a depth of at least
25 cm (Garren, 1913; Heyward, 1937, 1939). Suman and Halls (1955)
found a reduced infiltration wociated with an increase in bulk density
of the soil on areria that were burned annually for 7 years in Georgia.
These authors point out that compaction of soil on burned areas may
not be due to burning so much as to cattle concentrating their grazing
on such land.
Although a single burn in a stand of annual grass near Berkeley,
California, resulted in dwarfing the next generation of plants and reducing productivity somewhat, no difference in soil moisture levels
could be detected (Hervey, 1949). Another study in California involving
the relation of fire to the hydrology of woodland/graas vegetation also
ended without conclusive evidence that fire is detrimental to water
conservation in that state (Adams et al., 1947). It may be significant
that these accordant records of inconsequential change in soil moisture
status following grassland fires come from an area where most graa
growth is in the wet winter season, with soils desiccating apparently
equally during the dry season of herbaceous aestivation.
Moisture was observed to penetrate more deeply in unburned than
in burned areas of B o t h r y o c h ewartiana grmsland in Queensland
(Everist, 1939).
In east central and southern Africa, fire reduces the water-retaining
capacity of the soil and its water content falls lower during the dry
months so that the grass is more subject to drought injury (Cook, 1939;
Phillips, 1919; Scott, 1934; West, 1965), these results being strikingly
similar to those in Kansas reviewed above. On burned areas fluctuations
in water content were much wider than on unburned grasslands (Cook,
1939, 1965; Phillips, 1919). Also in southern Africa it has been observed
that the degree of drought of burned areas becomes greater the drier
the climate (West, 1965).
E. SOIL CHEMISTRY
1. The ash increment
It is well known that in the combustion of plant tissue N and S are
volatilized whereas all other nutrients are changed to simple salts that
aro water soluble and hence immediately available. This raises a question as to the possible role of the ash increment as a fertilizer for
subsequent plant development.
In forest vegetation where a great volume of shoot material is ashed
by a holocaust, it hae been well established that the ash increment
serves as a fertilizer of considerable significance, but in grw vegetation
225
changing fine crumb structure to single-grained or massive. These
changes do not alter the moisture-retaining capacity of the soil, but its
moisture content is lowered on the burned areas to a depth of at least
25 cm (Garren, 1913; Heyward, 1937, 1939). Suman and Halls (1955)
found a reduced infiltration wociated with an increase in bulk density
of the soil on areria that were burned annually for 7 years in Georgia.
These authors point out that compaction of soil on burned areas may
not be due to burning so much as to cattle concentrating their grazing
on such land.
Although a single burn in a stand of annual grass near Berkeley,
California, resulted in dwarfing the next generation of plants and reducing productivity somewhat, no difference in soil moisture levels
could be detected (Hervey, 1949). Another study in California involving
the relation of fire to the hydrology of woodland/graas vegetation also
ended without conclusive evidence that fire is detrimental to water
conservation in that state (Adams et al., 1947). It may be significant
that these accordant records of inconsequential change in soil moisture
status following grassland fires come from an area where most graa
growth is in the wet winter season, with soils desiccating apparently
equally during the dry season of herbaceous aestivation.
Moisture was observed to penetrate more deeply in unburned than
in burned areas of B o t h r y o c h ewartiana grmsland in Queensland
(Everist, 1939).
In east central and southern Africa, fire reduces the water-retaining
capacity of the soil and its water content falls lower during the dry
months so that the grass is more subject to drought injury (Cook, 1939;
Phillips, 1919; Scott, 1934; West, 1965), these results being strikingly
similar to those in Kansas reviewed above. On burned areas fluctuations
in water content were much wider than on unburned grasslands (Cook,
1939, 1965; Phillips, 1919). Also in southern Africa it has been observed
that the degree of drought of burned areas becomes greater the drier
the climate (West, 1965).
E. SOIL CHEMISTRY
1. The ash increment
It is well known that in the combustion of plant tissue N and S are
volatilized whereas all other nutrients are changed to simple salts that
aro water soluble and hence immediately available. This raises a question as to the possible role of the ash increment as a fertilizer for
subsequent plant development.
In forest vegetation where a great volume of shoot material is ashed
by a holocaust, it hae been well established that the ash increment
serves as a fertilizer of considerable significance, but in grw vegetation