ECOLOGY OF FIRE IN GRASSLANDS
233
is provided by vegetation recovering from a burn, rather than by
freshly burned or by long-unburned vegetation (Tester and Marshall,
1961). Cokopteru are most abundant in recent burns where there is negligible litter cover. Burlling affords some measure d control over insect
pests in grass plantations in Washington (Crawford & Harwood, 1964).
Most ungulates of open grassy vegetation are so fleet of foot that
fully grown individuals usually escape death from grwland fires, but
their young are frequently destroyed (Phillips, 1965).
The literature is replete with references to the attractiveness of new
grass on recent burns for hooved grazing animals. Also there are quantitative data showing that cattle make imprmsively greater gains in
weight when grazing on recently burned versus long-unburned grassland (Anderson, 1964; Greene, 193513; Wahlenberg et ul., 1939).
The increased palatability of grass on fresh burns poses a problem in
using fire in range management, for if animals are given access to the
new gram, they crop it heavily leaving insufficient photosynthetic
tissue to allow the plants to recover. But this situation can sometimes
be wed to advantage. Molinia cueruleo is mainly unpalatable except
just after a burn, 80 that if small ~IWW are burned, then subsequently
grazed heavily, Molinia is severely damaged and in part replaced by
more desirable species (Grant, 1963).
4. Unguluh
V. EFFECT ON THE INDIVIDUAL VASCULAR PLANT
A . DAMAGE
Byram (1948) considered 60°C as a reasonable approximation of the
lethal temperature for the shoot tissues of land plants, but some report
this threshold as low as 45°C whereas cacti can endure levels well above
60°C (Baker, 1929). The significance of these values is limited because
heat damage is dependent in part on time. A brief period at very high
temperature can cause injury equal to R longer exposure to a somewhat
lower temperature. The damage sustained in consequence of a given
fire is determined in large measure by the current temperature of plante
and litter, as this determines the quantity of heat required to bring
tissue temperatures up to the lethal threshold. If 60°C can be assumed
a lethal threshold for leaf tiesue, a leaf exposed to summer sun may
have a temperature of 36°C and an increase of only 25°C would be fatal.
In winter when leaf temperature drop8 close to freezing, much more
heat would be required for the same effect. Then when leaf temperatures
drop a few degrees below 0°C 80 that much of the water contained in
the tissue becomes frozen, heat tolerance incremes markedly owing to
233
is provided by vegetation recovering from a burn, rather than by
freshly burned or by long-unburned vegetation (Tester and Marshall,
1961). Cokopteru are most abundant in recent burns where there is negligible litter cover. Burlling affords some measure d control over insect
pests in grass plantations in Washington (Crawford & Harwood, 1964).
Most ungulates of open grassy vegetation are so fleet of foot that
fully grown individuals usually escape death from grwland fires, but
their young are frequently destroyed (Phillips, 1965).
The literature is replete with references to the attractiveness of new
grass on recent burns for hooved grazing animals. Also there are quantitative data showing that cattle make imprmsively greater gains in
weight when grazing on recently burned versus long-unburned grassland (Anderson, 1964; Greene, 193513; Wahlenberg et ul., 1939).
The increased palatability of grass on fresh burns poses a problem in
using fire in range management, for if animals are given access to the
new gram, they crop it heavily leaving insufficient photosynthetic
tissue to allow the plants to recover. But this situation can sometimes
be wed to advantage. Molinia cueruleo is mainly unpalatable except
just after a burn, 80 that if small ~IWW are burned, then subsequently
grazed heavily, Molinia is severely damaged and in part replaced by
more desirable species (Grant, 1963).
4. Unguluh
V. EFFECT ON THE INDIVIDUAL VASCULAR PLANT
A . DAMAGE
Byram (1948) considered 60°C as a reasonable approximation of the
lethal temperature for the shoot tissues of land plants, but some report
this threshold as low as 45°C whereas cacti can endure levels well above
60°C (Baker, 1929). The significance of these values is limited because
heat damage is dependent in part on time. A brief period at very high
temperature can cause injury equal to R longer exposure to a somewhat
lower temperature. The damage sustained in consequence of a given
fire is determined in large measure by the current temperature of plante
and litter, as this determines the quantity of heat required to bring
tissue temperatures up to the lethal threshold. If 60°C can be assumed
a lethal threshold for leaf tiesue, a leaf exposed to summer sun may
have a temperature of 36°C and an increase of only 25°C would be fatal.
In winter when leaf temperature drop8 close to freezing, much more
heat would be required for the same effect. Then when leaf temperatures
drop a few degrees below 0°C 80 that much of the water contained in
the tissue becomes frozen, heat tolerance incremes markedly owing to