BUSH FIRES AS AN ECOLOGICAL 
FACTOR IN THE PRESERVATION 
OF THE NATIVE FLORA 
By EDGAR W. PRITCHARD 
After the disastrous bush fires of last 
summer, there appeared in the daily press a 
good deal of discussion on methods of deal- 
ing with them when they occur; but few sug- 
gestions on how to prevent them altogether. 
This, of course, is the real problem, and the 
following is a contribution to that end. 
WHAT IS ECOLOGY? 
Let us look first at the scientific aspect. 
Ecology is that branch of science which deals 
with the relation of plants to their environ- 
ment, the environment consisting chiefly of 
the climate and the soil. To show that each 
environment produces a different type of 
plant it is only necessary to compare the 
flora of the sea shore, the Mount Lofty Range 
and the salt bush country. 
OUR SCLEROPHYLL FOREST 
But besides the soil and the climate there 
are other minor factors which influence the 
floral type of any particular area. And in 
the sclerophyll (hard leaf) forest of the Mt. 
Lofty Range, with its wet winter and dry 
summer, one of them is the periodical bush 
fire. 
BUSH FIRES PERENNIAL 
Now it is practically certain that this area 
has been burnt over frequently for hundreds 
of years. This is proved by the want of 
humus in the soil. Good soils are formed 
by the decay of grass or leaves, sticks and 
bark. In moist climates, where there are no 
forest fires, the vegetable debris covering 
the sail may be six feet and more deep. 
This gradually decays, and is worked into 
the soil by beetles and worms, and forms 
the dark brown humus, which is so essential 
for high fertility. I have observed one case 
under red gum trees, in which three inches 
of debris accumulated in ten years, which 
means 30 inches in 100 years, as well as some 
black top soil. The only reason why there 
is practically no humus in the sclerophyll 
forest soil is that the frequent bush fires destroy 
all the humus forming materials. It is true 
also that these soils are deficient in mineral 
plant foods, such as phosphates of lime, but 
this is due to the high rainfall. But on the 
other hand humus helps to hold these miner- 
als in the soil. 
COMPLETE DESTRUCTION 
Each hush fire burns up all the refuse on 
the surface, leaving behind little organic 
matter but charcoal. Then the winter rains 
come, and wash even this away into the 
gullies and out to sea. The reason why the 
gullies are more fertile is because they con- 
tain more moisture, and so are not burnt out 
so completely. So it appears that the scler- 
phyll forest of our Mt. Lofty Range must 
have been burnt over periodically for very 
many years. Their starting was probably 
due to the aborigines lighting the underbrush 
to drive out the game, as is still done in the 
northern interior. 
FIRE RESISTANT TYPES OF PLANTS 
And here ecology comes in again. This 
periodical burning off has become part of the 
conditions, the environment, in which the 
Page Thirty -two 
