230
It. I)AllllENMIfllc,
quantitiw of C ' I L ~ ~ ) O ~ ~ ( : U O I I H
msbrial in burning might reduce the C/N
ratio of thc mil, rnikkirig N more availnble, but in Quecnsland, Australia,
burning that hurl beon seven: enough to pedestal the individual plants
and thin a stand of Heteropogon contortus changed neither the C nor N
content of the soil (Shaw, 1957). If derived savanna in Nigeria is
burned early in the dry seaaon so that the heat is only moderate,
grasses are invigorated, nitrification is greatly increased, and humus
is slightly increased, but hot fires later in the s e w n have the opposite
effect (Moore, 1960). However, both types of fire raise the C/X ratio
about equally, in comparison with unburned savanna.
F. MICROCLIMATE
Drastic changes in microclimate a t the soil-atmosphere interface are
brought about by burning a stand of grass. Where perennials are
dominant and regenera,te shoots promptly, this environmental alteration is short-lived, but where annuals are important constituents of the
vegetation and their seeds have been largely destroyed, or where perennials have been seriously damaged, the changed conditions bring about
considerable alteration of community composition and structure that
may last for Reveral years. The details of such alterations have been
abundantly documented by phytosociologic data, but are hardly relevant in the present revicw. Records of the kind and degree of microclimatic changes that arc involved would be of concern here, but with
the exception of the limited temperature data that have been summarized, they are almost non-existent.
In New Zealand grasslands t,he post-burn decline of some of the minor
species has been interpreted as a consequence of a loss of some protect,ive influence of the dominant caespit,ose perennials that had been
damaged (Sewell, 1948). And in the same country Mark ( 1 9 6 5 ~ )
observed
die-back of leaf tips that was conspicuous in only a burned area, and
this may reflect microclimatic difference. I n southeastern United States
early spring burns can stimulate premature germination of the seeds
of desirable legumes so that they are devastatcd by frost (St.oddard,
1935a).
G . SOIL BIOTA
I n summarizing earlier work, Waksman (1927) concluded that artificially heating soil, using either steam or dry heat, renders the soil more
fertile, 80 long as the temperature remains below lOO"C, whereas heating above this level reduces ferti1it.y. Waksman further stated that the
increase in fertility is accompanied hy an increase in soluble matter,
and by microbiologic c h i m p that increase the relative dominance of
It. I)AllllENMIfllc,
quantitiw of C ' I L ~ ~ ) O ~ ~ ( : U O I I H
msbrial in burning might reduce the C/N
ratio of thc mil, rnikkirig N more availnble, but in Quecnsland, Australia,
burning that hurl beon seven: enough to pedestal the individual plants
and thin a stand of Heteropogon contortus changed neither the C nor N
content of the soil (Shaw, 1957). If derived savanna in Nigeria is
burned early in the dry seaaon so that the heat is only moderate,
grasses are invigorated, nitrification is greatly increased, and humus
is slightly increased, but hot fires later in the s e w n have the opposite
effect (Moore, 1960). However, both types of fire raise the C/X ratio
about equally, in comparison with unburned savanna.
F. MICROCLIMATE
Drastic changes in microclimate a t the soil-atmosphere interface are
brought about by burning a stand of grass. Where perennials are
dominant and regenera,te shoots promptly, this environmental alteration is short-lived, but where annuals are important constituents of the
vegetation and their seeds have been largely destroyed, or where perennials have been seriously damaged, the changed conditions bring about
considerable alteration of community composition and structure that
may last for Reveral years. The details of such alterations have been
abundantly documented by phytosociologic data, but are hardly relevant in the present revicw. Records of the kind and degree of microclimatic changes that arc involved would be of concern here, but with
the exception of the limited temperature data that have been summarized, they are almost non-existent.
In New Zealand grasslands t,he post-burn decline of some of the minor
species has been interpreted as a consequence of a loss of some protect,ive influence of the dominant caespit,ose perennials that had been
damaged (Sewell, 1948). And in the same country Mark ( 1 9 6 5 ~ )
observed
die-back of leaf tips that was conspicuous in only a burned area, and
this may reflect microclimatic difference. I n southeastern United States
early spring burns can stimulate premature germination of the seeds
of desirable legumes so that they are devastatcd by frost (St.oddard,
1935a).
G . SOIL BIOTA
I n summarizing earlier work, Waksman (1927) concluded that artificially heating soil, using either steam or dry heat, renders the soil more
fertile, 80 long as the temperature remains below lOO"C, whereas heating above this level reduces ferti1it.y. Waksman further stated that the
increase in fertility is accompanied hy an increase in soluble matter,
and by microbiologic c h i m p that increase the relative dominance of