Discussion paper, May 2014; written for a subject in BSc course.
Many Australian plant
species and ecological communities have evolved to cope with, benefit
from or even rely on fire (Bowman, 2012). There is little debate
that the Indigenous peoples of Australia prior to European
colonisation also used fire widely including for clearing vegetation
and hunting, and that they effected some changes on the ecology of
the continent.
The exact nature of
those changes, and the role of fire specifically, however, is a more
contentious topic, and hard to settle conclusively with the evidence
currently available (Kirkpatrick, 1999; Kohen, 1993).
This paper will explore
several of the key lines of argument and dispute, examine some of the
evidence they are based on, and suggest how well current research may
be able to answer the question (or not).
The initial impact of Indigenous fire
While many reports by
early European explorers note the frequency with which Indigenous
people set fire to country, little scientific recognition of
Indigenous fire management was extended by mainstream Australia until
the 1960s (Flannery, 1994; Kohen, 1993).
Current recognition of
the importance of Indigenous fire management, as in Gammage (2011),
has not been matched by a growing clarity as to the specifics of
Indigenous fire regimes in times past, nor their exact impact on the
environment.
It has been postulated
that the arrival of the First Peoples, currently understood to have
been at least 40ka [40,000 years ago] (Gott, 2005), was followed by a more or less rapid
conversion of ecosystems by the use of fire (Flannery, 1994).
According to various
versions of this argument, fire regimes after the arrival of the
first people stimulated the rapid spread and dominance of the
fire-tolerant genera of plants (Flannery, 1994, pp. 230-1); and even
their speciation and radiation (cited in Bowman, 2012).
Recent work on
molecular phylogenies suggests that the evolution of Australia's
fire-adapted species and ecosystems happened in the order of 55-60Ma [million years ago],
and that they became more dominant after 15 Ma. Features that make
species fire-tolerant or dependent, such as oil glands in the leaves,
may have evolved for reasons not related to fire, such as to deter
browsing animals (Bowman, 2012).
This evidence does not
rule out a significant impact by Indigenous fires on the distribution
of species and ecosystems (Bowman, 2012; Kirkpatrick, 1999).
Evidence of the
long-term fire and vegetation record is largely drawn from analysis
of charcoal residue and pollen in core samples from sedimentary
deposits. Not all sites show unequivocal evidence for a significant
increase in burning with the presumed arrival dates of the first
people, and fire has a long and definite history on the continent
prior to human occupation (Bowman, 2012).
Complicating factors
influencing fire include drying out in glacial periods, and faster
vegetation growth in warmer, wetter periods. These complex factors of
interaction make it hard to distinguish Indigenous fire's effects
(Bowman, 2012; Kohen, 1993).
Some sedimentary
analyses have found (for example) charcoal increases at the boundary
between earlier layers dominated by rainforest, and later layers
dominated by sclerophyll vegetation. It has been difficult to
conclusively date these layers, however (Bowman, 2012), and given the
continuing uncertainty about the exact time of arrival of the first
people in Australia, and other factors mentioned above hard to know
the cause of such fire events.
Understanding the
background rate of natural fires (from lighting strikes) and their
impact on vegetation is key to understanding how Indigenous fire may
have moderated, prevented, or increased the background fire rate in
any given ecosystem, and how much of a change the Indigenous arrival
presented, or how much change was caused by the end of Indigenous
fire in recent times (see for example Fensham, 2012). Lighting
remains the major cause of fire in some parts of tropical Australia
(Kohen, 1993).
One soils study found
strong evidence that erosion increased significantly around 35-30ka
with evidence of fire at the same time, in Tasmania where lighting
fires are relatively rare. This is around the time Indigenous people
are most commonly thought to have arrived there.
This lends some weight to the idea that significant impact on the
landscape occurred, but it is not conclusive. (McIntosh et
al, 2008).
On
the other hand, genetic analysis has been used to show that
fire-sensitive Callitris
cypress-pine populations have not experienced significant population
crashes as would have been caused by widespread hot fire on the
arrival of Indigenous people (Sakaguchi et al,
2013).
Measuring Indigenous impact by its absence
While the scale of the
initial impact of the first peoples' fire is hard to judge from
existing records, its ongoing influence on the ecology of the
continent is easier to find evidence for.
Along the east coast
and northern Australia, rainforest ecosystems have spread to areas
which were open woodland or sclerophyll forest at the time of
European arrival (Flannery, 1994; Kirkpatrick, 1999; Fensham, 2012;
Bowman, 2012). Mechanisms for the return of rainforest appear to
include protection from fire, including lighting-lit fires (Fensham,
2012), but possibly also changed rainfall and atmospheric CO2
for some locations (Bowman, 2012).
The spread of
rainforest can be verified by comparing current vegetation to
historical records (Flannery, 1994; Gammage, 2011). It is known that
some areas now rainforested were, at the time of European arrival in
Australia, kept as open woodland by Indigenous burning (McIntosh et
al, 2009).
The knowledge of
Indigenous hunting includes widespread reference to the use of fire
(Flannery, 1994; Gammage, 2011). Indigenous use of food plants in
many areas also depended on fire. For example, without frequent fire
(every 3-5 years in many locations), grassland and grassy woodland
regenerates a thick sward that smothers small tuberous food plants
that provided a large proportion of the diet for people living in
those areas (Gott, 2005).
It is clear that in
many areas, including areas still under Indigenous fire management in
the arid centre and northern Australia, Indigenous fire management
enhanced and enhances local biodiversity by preventing hot wildfire
(fuel reduction), and by maintaining a fine patchwork or mosaic where
each patch has been burned at different times, with some patches
burned infrequently or not at all (Kohen, 1993; Bowman, 2012; Altman
and Kerins, 2012; Fensham, 2012).
It has been argued that
the cessation of Indigenous burning (and the introduction of a new,
different fire regime) has caused ecosystem changes that have led to
some mammal species becoming endangered or extinct (Flannery, 1994).
While this hypothesis is very plausible, it requires further testing
for specific locations and species instances (Fensham, 2012).
Whether Indigenous fire
resulted in widespread extinction of mammals or other biota following
the First Peoples' arrival is also uncertain, as the exact date of
the megafauna extinctions, and the cause, is still hotly debated;
some scientists have even argued that evidence supports long
co-existence of megafauna alongside people for at least 15000 years
(Trueman et al, 2005).
Conclusion
There is some evidence
to suggest that the arrival of the First People to the Australian
continent resulted in fairly rapid changes to ecosystems as a result
of fires. The exact degree of the changes is difficult to quantify.
At the least, it can be reliably assumed that change to the
distribution, boundaries, and diversity of many ecosystems was caused
by Indigenous fire, possibly including protecting species that would
otherwise have become extinct (or which may now become extinct,
having adapted to the Indigenous fire regime – Fensham, 2012).
There is some evidence that the impact was much greater, initially,
including widespread erosion, and maybe even regional climatic
change.
Difficulties in
assessing the ongoing impact of Indigenous fire arise from the
paucity of reliable fossil or archaeological record, uncertainties in
dating samples, and lack of understanding or record of the diverse
practices of Indigenous people prior the British conquest.
Nevertheless, the historical record (including Indigenous knowledge)
has provided enough information for ongoing debate.
At one extreme, it has
been argued that almost all of Australia was burned regularly under
Indigenous management, perhaps as often as every 2-5 years (Gammage,
2011). On the other hand, evidence from current Indigenous practice
and knowledge directly contradicts this uniformitarian generalisation
(Prober et al, 2013; Morgan, 2013). It seems most likely that
Indigenous fire management varied across the different climatic and
vegetation regions of the continent, but even then the degree of
variation is not certain. Current research available cannot tell us
whether Gammage's unfortunate generalisation is nevertheless widely
applicable, or in fact wildly inaccurate.
Further evidence from
investigation in social and physical sciences is needed to make
significant progress in answering this question. Doing so will not
only shed light on the events and practices of the past, but provide
a scientific basis for ecological fire management for conservation
into the future.
References
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on Country: Vital Landscapes Indigenous Futures,
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Bowman, D.M.J.S, Murphy, B.P., Burrows, G.E., &
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(2012). Flammable Australia, Melbourne,
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