224
R. DAUBENMIRE
favor drought. h t m in the growing r)eason the larger lcaf-area index,
that often characterizes fire-stimulated plants, results in greater transpiration with increased withdrawal of water from lower layers in the
soil profile, in comparison with an unburned area. Even in an unburned
condition grassland commonly allows loss of water by surface run-off,
and after a fire run-off increases (Hanks and Anderson, 1957). The
steeper the slope and the longer the interval between burning and the
development of a new vegetative cover, the greater the run-off and the
likelihood of erosion being induced.
Other factors tend to conserve soil moisture on burned areas. Interception losses, which can be as high in grassland as in forest (Burgy
and Pomeroy, 1958; Clark, 1940), are eliminated when fire removes
living shoots and litter. Then in situations where the post-burn vegetation is thinner, or has a higher proportion of early-maturing species, or
a higher proportion of shallow-rooting species, there may be less depletion of soil moisture through transpiration.
In a grass-dominated heath in Britain it was observed that the surface 25 mm of the soil became relatively dry after the vegetation had
been burned off, whereas the 5-18 cm horizon became relatively wet
(Eden, 1924).
In those parts of the United States where there is appreciable summer
precipitation, the moisture-dissipating forces prevail in recently burned
grassland. In an area dominated by perennial species of Poa and forbs
in Illinois, soil moisture proved to be equal on burned and unburned
parts in early spring, but after mid-April the soil dried out faster on the
burn (Rice, 1932). Burned grassland in Iowa was drier in the upper
10 cm of the profile from mid-May to at leaat 1 October, although it
never became critically low (Ehrenreich and Aikman, 1963). Regular
burning of Adropogon scoparim steppe in eastern Kansas, regardless
of the season of burning, reduced the average moisture content of the
Roil in summer to a depth of a meter so that plants on burned areas
showed distinctly more drought symptoms (Aldous, 1934; Anderson,
1904; Hanks and Anderson, 1957; McMurphy and Anderson, 1965); the
earlier the date of burning in winter and spring the greater the reduction
(Anderson, 1964, 1965). In these steppes burning leads to reduced infiltration (Hanks and Anderson, 1957; McMurphy and Anderson, 1965).
It also lowered the field capacity and wilting coefficient on uplands,
but not on a lowland site where there WM initlially more clay in the
soil (Anderson, 1964).
Regular firing of open pine forest on the Comtial Plain of southeastern
North America secms always to reduce infiltration, which may be
attributed to decreasing the soil fauna which keeps porosity high in
the A , horizon (Heyward, 1936; Heyward and Barnette, 1934), and to
R. DAUBENMIRE
favor drought. h t m in the growing r)eason the larger lcaf-area index,
that often characterizes fire-stimulated plants, results in greater transpiration with increased withdrawal of water from lower layers in the
soil profile, in comparison with an unburned area. Even in an unburned
condition grassland commonly allows loss of water by surface run-off,
and after a fire run-off increases (Hanks and Anderson, 1957). The
steeper the slope and the longer the interval between burning and the
development of a new vegetative cover, the greater the run-off and the
likelihood of erosion being induced.
Other factors tend to conserve soil moisture on burned areas. Interception losses, which can be as high in grassland as in forest (Burgy
and Pomeroy, 1958; Clark, 1940), are eliminated when fire removes
living shoots and litter. Then in situations where the post-burn vegetation is thinner, or has a higher proportion of early-maturing species, or
a higher proportion of shallow-rooting species, there may be less depletion of soil moisture through transpiration.
In a grass-dominated heath in Britain it was observed that the surface 25 mm of the soil became relatively dry after the vegetation had
been burned off, whereas the 5-18 cm horizon became relatively wet
(Eden, 1924).
In those parts of the United States where there is appreciable summer
precipitation, the moisture-dissipating forces prevail in recently burned
grassland. In an area dominated by perennial species of Poa and forbs
in Illinois, soil moisture proved to be equal on burned and unburned
parts in early spring, but after mid-April the soil dried out faster on the
burn (Rice, 1932). Burned grassland in Iowa was drier in the upper
10 cm of the profile from mid-May to at leaat 1 October, although it
never became critically low (Ehrenreich and Aikman, 1963). Regular
burning of Adropogon scoparim steppe in eastern Kansas, regardless
of the season of burning, reduced the average moisture content of the
Roil in summer to a depth of a meter so that plants on burned areas
showed distinctly more drought symptoms (Aldous, 1934; Anderson,
1904; Hanks and Anderson, 1957; McMurphy and Anderson, 1965); the
earlier the date of burning in winter and spring the greater the reduction
(Anderson, 1964, 1965). In these steppes burning leads to reduced infiltration (Hanks and Anderson, 1957; McMurphy and Anderson, 1965).
It also lowered the field capacity and wilting coefficient on uplands,
but not on a lowland site where there WM initlially more clay in the
soil (Anderson, 1964).
Regular firing of open pine forest on the Comtial Plain of southeastern
North America secms always to reduce infiltration, which may be
attributed to decreasing the soil fauna which keeps porosity high in
the A , horizon (Heyward, 1936; Heyward and Barnette, 1934), and to