246
R. I)AUBENJIIRE
specificity often being conspicuous in the field where associated species
show divergent responses to the same fire.
Vigor and vitality responses are commonly reversed in that a shift of
relative emphasis from vegetative to flowering activity is very common
(Burton, 1944; Curtis and Partach, 1950; Dix and Butler, 1954; Ehrenreich, 1959). However in the same stand in Wisconsin, inflorescence
production in Boutelowl curtipendub remained constant while coverage
increased, whereas in Sporobolw lleterolepis both inflorescences and
coverage increased (Dix and Butler, 1954).
In eastern Tdaho flowering was not vigorous until the second postburn summer (Blaisdell, 1983), with the same true of Deschampsia
pexuosa in Britain (Grant et al., 1963) and Chionochh rigida in New
Zealand (Mark, 19651, 1965~). Grant suggested that this pattern of
response in which stimulation is delayed until the second post-burn
season probably results from the higher temperature of the fire-bared
soil, perhaps operating in conjunction with day length, to initiate many
flower primoidea that produce abnormal numbers of flowering culms
the following year. Mark (1965~) agrees with this interpretation.
Usually the positive flowering stimulus is short-lived, lasting only
two years in Iowa (Ehrenreich and Aikman, 1963), Wisconsin (Dix and
Butler, 196P), and eastern Illinois (Hadley and Kiekhefer, 1963), and
but a single season for burned Chionochloa rig& in New Zealand (Mark,
1965~). In the last instance, t,he fire that increased the number of inflorescences also reduced their height, dwarfed the size of the florets and
caryopses and reduced the viability of the latter.
It has been suggested that the low vitality of unburned grass is a
result of self-generated microclimate*accruing from the litter accumulation (O’Connor and Powell, 1963). Robertson (1953) in Florida, Mark
(1965c), in New Zealand, and Curtis and Partach (1950) in Wisconsin
have provided evidence in favor of this hypothesis by mechanically
removing litter and getting increased vitality as with burning. In h r t i s
and Partsch’s experiment the number of inflorescences increased by
600% and their heights by 60%. Of all their manipulations, simple
removal of litter seemed to account for most of the growth stimulation
observed following fire. They interpreted this as a result of litter shading
the newly emerging leaves in spring AO that it delayed their growth by
as much as threc to four weeks, thereby maintaining carbohydrate
reserves at a low level until after Aower primoidea are initiated, a conclusion supported by Ehrenreich and Aikman (1 957).
It has been thought that the need for repeated burning to maintain
grass in a healthy condition in wet climates is related to the higher
productivity and hence heavier litter cover (Kucera and Ehrenreich,
1962; West, 1965). The complexity of the phenomenon is shown by
R. I)AUBENJIIRE
specificity often being conspicuous in the field where associated species
show divergent responses to the same fire.
Vigor and vitality responses are commonly reversed in that a shift of
relative emphasis from vegetative to flowering activity is very common
(Burton, 1944; Curtis and Partach, 1950; Dix and Butler, 1954; Ehrenreich, 1959). However in the same stand in Wisconsin, inflorescence
production in Boutelowl curtipendub remained constant while coverage
increased, whereas in Sporobolw lleterolepis both inflorescences and
coverage increased (Dix and Butler, 1954).
In eastern Tdaho flowering was not vigorous until the second postburn summer (Blaisdell, 1983), with the same true of Deschampsia
pexuosa in Britain (Grant et al., 1963) and Chionochh rigida in New
Zealand (Mark, 19651, 1965~). Grant suggested that this pattern of
response in which stimulation is delayed until the second post-burn
season probably results from the higher temperature of the fire-bared
soil, perhaps operating in conjunction with day length, to initiate many
flower primoidea that produce abnormal numbers of flowering culms
the following year. Mark (1965~) agrees with this interpretation.
Usually the positive flowering stimulus is short-lived, lasting only
two years in Iowa (Ehrenreich and Aikman, 1963), Wisconsin (Dix and
Butler, 196P), and eastern Illinois (Hadley and Kiekhefer, 1963), and
but a single season for burned Chionochloa rig& in New Zealand (Mark,
1965~). In the last instance, t,he fire that increased the number of inflorescences also reduced their height, dwarfed the size of the florets and
caryopses and reduced the viability of the latter.
It has been suggested that the low vitality of unburned grass is a
result of self-generated microclimate*accruing from the litter accumulation (O’Connor and Powell, 1963). Robertson (1953) in Florida, Mark
(1965c), in New Zealand, and Curtis and Partach (1950) in Wisconsin
have provided evidence in favor of this hypothesis by mechanically
removing litter and getting increased vitality as with burning. In h r t i s
and Partsch’s experiment the number of inflorescences increased by
600% and their heights by 60%. Of all their manipulations, simple
removal of litter seemed to account for most of the growth stimulation
observed following fire. They interpreted this as a result of litter shading
the newly emerging leaves in spring AO that it delayed their growth by
as much as threc to four weeks, thereby maintaining carbohydrate
reserves at a low level until after Aower primoidea are initiated, a conclusion supported by Ehrenreich and Aikman (1 957).
It has been thought that the need for repeated burning to maintain
grass in a healthy condition in wet climates is related to the higher
productivity and hence heavier litter cover (Kucera and Ehrenreich,
1962; West, 1965). The complexity of the phenomenon is shown by