Byron Flora and Fauna Study 1999 - Byron Shire Council

BYRON FLORA AND FAUNA STUDY, 1999
histories of the component species. Species which are killed by fire and which reproduce by seed require a
fire frequency in excess of the time taken to reach reproductive maturity. Species requiring fire to stimulate
seed germination need a fire frequency less than the length of time that the seeds remain viable.
Fire can play a major role in causing what are often irreversible and self-perpetuating changes to ecosystems.
For example, weed species often establish following disturbance by fire and may alter the fuel load and
distribution, engendering favourable conditions for more fires.
Modifications to vegetation by fire have flow-on effects on fauna species in relation to their requirements
for food resources, shelter and breeding sites. Too frequent burning removes ground cover vegetation and
the litter layer destroying the food of many terrestrial species and exposing some to increased levels of
predation. The incidence of collapse of senescent trees is increased, removing breeding sites for hollowdependent
species and the loss of large logs is also increased, destroying shelter sites for other vertebrates.
There is little documentation of fire effects on the ecology of Byron Shire. Natural ignition (lightning) is
believed to be rare in the region; most fires are started by arson or the escape of deliberately lit fires.
For Whian Whian State Forest, Turner (1984) provided an indication of the fire regime in pre-European
times, though not for pre-Aboriginal times. Using carbon dating techniques, he estimated that the most
frequent fires in a Blackbutt stand were approximately every 280 years. He also estimated on average a fire
frequency of every 300 to 400 years for Brush Box. The last single fire in the rainforest was around 1100
years ago; this was the only evidence of fire.
Something of the fire history can be deduced from an examination of present day vegetation. For instance,
in the upper Brunswick Valley, where soil and climatic conditions would other-wise favour rainforest, the
vegetation is dominated by eucalypt and Brush Box forest. This may be a legacy of Aboriginal burning,
carried on in similar fashion by farmers until quite recently. In the Brunswick-Tweed area, high rainfall, the
short dry season and the rarity of dry lightning storms, even during El Nino years, all suggest that natural
ignition would not have been frequent enough to maintain the extensive areas of wet sclerophyll forest and
prevent its succession to rainforest. The only explanation for vegetation patterns is the operation of humanlit
fires – Aboriginal followed by European. In pre-European times, the pattern of landscape burning (given
Aboriginal ignition) would also have been determined by variations in weather patterns, which probably
followed the cycle of El Nino/La Nina. In dry El Nino years uncontrolled fires were probably more frequent,
with wild fires burning deeply into rainforests (A. Benwell pers. comm.).
The longevity of Brush Box (up to 1340 years, Turner (1984)), indicates that the succession of Brush Box
forest to rainforest probably requires a few thousand years. The long fire-free period needed for this succession
would have been unlikely after human ignition became established in the landscape. Exceptionally dry
conditions during the last glacial maxima, may have seen very destructive fires in rainforests and the expansion
of sclerophyll vegetation including Brush Box. Once established, sclerophyll communities can be perpetuated
by human burning and prevented from returning to rainforest (A. Benwell pers. comm.).
The presence of coastal heathland dominated by the fire-requiring Heath-leaved Banksia in the humid
climatic environment of Byron Shire can only be explained by the operation of human-lit fires for a long
period of time. Natural fires are most unlikely in coastal Byron Shire because of the climate and the nonflammable
rainforest communities behind the heath. Heath-leaved Banksia lives for 25-30 years and to
persist in the landscape fires have to burn the heath in which it occurs every 5-25 years. The abundance of
this species in coastal heaths indicates that such a fire regime has prevailed for a long time (A. Benwell
pers. comm.).
Benwell (1986, undated) has studied fire history and floristics in Tyagarah Nature Reserve, and identified a
mosaic of vegetation types with differing fire responses. In particular, he compared burnt and unburnt
heath, and estimated that nine species disappeared between 1984 and the penultimate fire, 10 years previously.
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