ECOLOGY OF FIRE IN ORASSLANDS
235
Plants with different growth forms may fare differently as a result of
the same burn. In eastern Idaho it was observed that rhizomatous and
annual steppe grasses were stimulated by burning, whereas suffrutescent associates as a class were damaged by the same fire (Blaisdell,
1953).
In theory the bulk of a seed or an organ has a bearing on its susceptibility to heat damage, for the smaller the organ the more quickly it is
brought up to the lethal temperature (Byram, 1948).
The positions of seeds and buds at the time of burning is critical. In
western Kansas it was observed that the higher the elevation of the
perennating buds the more heavily fire damaged steppe plants (Hopkins
et al., 1948). The negligible effects of burning on Aristdu stricta and
Sporobolus curtisii in Georgia was attributed to the positions of the leaf
meristems at 38 mm or more below the soil surface (Lemon, 1949). In
Oregon a fire was much more detrimental to Festuca idahoensia than to
Agropyrmt epicaturn, and it was pointed out that in the former the buds
were closely spaced and located at or above the ground surface, whereas
in Agropyron the buds are widely spacod and situated below the ground
surface (Conrad and Poulton, 1966).
Ariste'da stricta and Spcwobolus $oridanus have closely packed persistent leaf sheaths which exclude oxygen and so do not burn, thus
providing good insulation for their buds (Lemon, 1949). I n the savannas
of central Brazil many species of grasses and other herbs escape damage
by the frequent fires because dead leaves form a tunic about the
perennating bud8 (Rachid-Edwards, 1956). The resistance of Celmisia
spectabilis to burning in New Zealand appeare to be a consequence of
the moisture-holding sheaths of living and dead leaves (Barker, 1953).
The stems and leaves of annuals commonly dry to the point of becoming flammable while their seeds are still ripening in the inflorescences. As a result fire may Rweep the area while the seeds are held aloft
where heat is most intense (Bentley and Fenner, 1958; Furbush, 1963;
McKell et nl., 1962; Major et at?., 1960; Pechanec and Hull, 1945). Since
solar radiation can heat a soil to 60°C and maintain this level for hours,
i t seemed unlikely to Vareschi (1962) that temperature of 90°C at the
4 soil surface, whioh would be sustained for only a few seconds as a fire
paased, would do much harm to seeds and buds normal to this position.
Laboratory tests confirmed this hypothesis, showing that the seeds of
dominant Venezuelan savanna grasses can endure 90°C for 40 sec. The
data available for the tolerance of seeds to dry heat are summarized
in Table I.
The higher the moisture content of annual grass caryopses the more
susceptible they have been found to heat injury, but the effect is small
(McKell et ul., 1962).
235
Plants with different growth forms may fare differently as a result of
the same burn. In eastern Idaho it was observed that rhizomatous and
annual steppe grasses were stimulated by burning, whereas suffrutescent associates as a class were damaged by the same fire (Blaisdell,
1953).
In theory the bulk of a seed or an organ has a bearing on its susceptibility to heat damage, for the smaller the organ the more quickly it is
brought up to the lethal temperature (Byram, 1948).
The positions of seeds and buds at the time of burning is critical. In
western Kansas it was observed that the higher the elevation of the
perennating buds the more heavily fire damaged steppe plants (Hopkins
et al., 1948). The negligible effects of burning on Aristdu stricta and
Sporobolus curtisii in Georgia was attributed to the positions of the leaf
meristems at 38 mm or more below the soil surface (Lemon, 1949). In
Oregon a fire was much more detrimental to Festuca idahoensia than to
Agropyrmt epicaturn, and it was pointed out that in the former the buds
were closely spaced and located at or above the ground surface, whereas
in Agropyron the buds are widely spacod and situated below the ground
surface (Conrad and Poulton, 1966).
Ariste'da stricta and Spcwobolus $oridanus have closely packed persistent leaf sheaths which exclude oxygen and so do not burn, thus
providing good insulation for their buds (Lemon, 1949). I n the savannas
of central Brazil many species of grasses and other herbs escape damage
by the frequent fires because dead leaves form a tunic about the
perennating bud8 (Rachid-Edwards, 1956). The resistance of Celmisia
spectabilis to burning in New Zealand appeare to be a consequence of
the moisture-holding sheaths of living and dead leaves (Barker, 1953).
The stems and leaves of annuals commonly dry to the point of becoming flammable while their seeds are still ripening in the inflorescences. As a result fire may Rweep the area while the seeds are held aloft
where heat is most intense (Bentley and Fenner, 1958; Furbush, 1963;
McKell et nl., 1962; Major et at?., 1960; Pechanec and Hull, 1945). Since
solar radiation can heat a soil to 60°C and maintain this level for hours,
i t seemed unlikely to Vareschi (1962) that temperature of 90°C at the
4 soil surface, whioh would be sustained for only a few seconds as a fire
paased, would do much harm to seeds and buds normal to this position.
Laboratory tests confirmed this hypothesis, showing that the seeds of
dominant Venezuelan savanna grasses can endure 90°C for 40 sec. The
data available for the tolerance of seeds to dry heat are summarized
in Table I.
The higher the moisture content of annual grass caryopses the more
susceptible they have been found to heat injury, but the effect is small
(McKell et ul., 1962).