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I. Introduction 3. CLASSIFICATION AND EXTENT
Australia's rainforests have been classified into five major types:
tropical, subtropical, dry, warm temperate, and cool temperate
rainforest. Warm temperate rainforest is distributed mainly in
southern Queensland and New South Wales. In Victoria, warm temperate
rainforest is confined to river valleys and associated gully systems
from Wilson's Promontory eastwards. Cool temperate rainforest
occurs predominantly in Tasmania and extends into New South Wales
and south-east Queensland with relatively small areas in Victoria
(Horne and Hickey 1991, Busby and Brown in press). Dry rainforest
is distributed from Queensland to Victoria in dry sites that are
protected naturally from fire (Gillison 1987) and is recognised
in New South Wales (Keith and Saunders 1990, Floyd 1990). From
a continental perspective, this rainforest type comprises about
half of all structural rainforest types, it is the least well
conserved rainforest type, it is floristically rich and ecologically
it is the least well known (Gillison 1987, Floyd 1990). In Victoria,
it is represented in very small patches scattered from the Mitchell
River east to the New South Wales border (Cameron 1992).
Under the definition of rainforest adopted by CNR (CFL 1987),
which may be regarded as ecologically narrow, and using aerial
photo interpretation at a scale of 1:100,000, about 15,800 ha
of mature rainforest exists in Victoria (Table 1). These data
exclude some secondary rainforest stands that conform to the rainforest
definition (CNR 1987) and exclude about 320 ha of unclassified
vegetation that is either warm or cool temperate rainforest, or
overlap communities. For the most recent data available (Table
2), the proportions of the 15,800 ha of rainforest in State Forest
are 71% of cool temperate rainforest and 64% of warm temperate
rainforest. About 30% of each of cool and warm temperate rainforest
types are protected in conservation reserves. Comparable data
for dry rainforest are not available.
Table 1. Area and number of
patches of each of two temperate rainforest types in Victoria
(data from Forest Information, CNR, 1994, pers. comm.). Data
for dry rainforest are not available. A patch is defined as a
single rainforest polygon on the GIS database, interpreted from
1:100000 aerial photography.
The use of rainforest definitions other than that adopted by CNR
may result in larger estimates of rainforest area. Inclusion
of small, linear stands, rainforest with sclerophyll emergents,
and secondary rainforest co-dominated by Acacia melanoxylon
resulted in an estimate of at least 25,000 ha of forest that falls
within Dale et al.'s (1980) definition of rainforest (Cameron
1992). AHC and CNR (1994) reported mapping by CNR of 12,979 ha
of cool temperate rainforest in the Central Highlands alone, using
a definition of rainforest that included secondary rainforest
stands but excluded mixed forest. It is important to note that
the report by AHC and CNR (1994) stated that the mapping process
tends to overestimate the extent of rainforest as defined by CFL
(1987). In any case, evaluation of other rainforest definitions
is beyond the scope of this review.
In East Gippsland, ecotones exist between cool temperate rainforest
and Montane Wet Forest and Wet Forest, and between warm temperate
rainforest and Damp Forest, Lowland Forest, Riparian Forest, Shrubby
Dry Forest and Rocky Outcrop Scrub (Woodgate et al. 1994).
Data on the proportion of each rainforest type that borders each
of these sclerophyll forest types are unavailable.
Table 2. Land tenure status
of Victoria's rainforests, based on data supplied by CNR, Forest
Information. Sites classed as having 'No information' include
polygons on the GIS database that have not yet been validated
by CNR, and those sites where the adequacy of the data have been
questioned. Some mapping at the 1:100 000 scale is yet to be
completed. Percentages are based on areas where mapping is complete
(the 'No information' category is ignored). 2a. Cool temperate rainforest
2b. Warm temperate rainforest
CFL (1987) reported 3900 ha of warm temperate rainforest and 9370
ha of cool temperate rainforest. The reasons for the differences
between the numbers provided by CFL (1987) and those based on
more recent data (Tables 1 and 2) are not clear, although it is
natural for estimates of the extent of rainforest to change as
new surveys at larger scales are completed. Differences between
the number of stands (Table 1) and the frequency of land tenure
(Table 2) are due to the fact that there are many stands in which
more than one tenure applies. There is also potential mapping
resolution uncertainty, resulting in more map intersections than
actually exist. Rainforest re-mapping is currently being undertaken
as part of the Department's Ecological Vegetation Class mapping
program.
Warm temperate and cool temperate rainforest have been differentiated
on the basis of field plots, using information on constituent
species and their relative abundances, their physiognomic properties,
and the characteristics of the environments in which they are
found. The floristic definitions are then interpreted on aerial
photographs, supported by ground truthing. Cool temperate rainforest
occurs in regions where the Mediterranean climate is ameliorated
by maritime or montane influences. Warm temperate rainforest
is found in drier, warmer, lowland and foothill regions. This
division into two primary types may be further refined using floristic
and structural attributes (Cameron 1992, see for example McMahon
1987, Melick 1990a, Woodgate et al. 1994).
and Brodribb River. This map sheet was chosen because it had the greatest number of rainforest polygons. The work required to compile complete information for all rainforest polygons within altitude classes would have been prohibitive (Forest Information Section, CNR, pers. comm.)
The distribution of rainforest is related to fire frequency, but
different types are related to topography and climate. For example,
in Figure 1, warm temperate rainforest is found at altitudes mostly
below 440 m. Both warm and cool rainforest types, and overlap
communities, occur in intermediate altitudes between 440 m and
860 m. In this area of East Gippsland, only cool temperate rainforest
occurs above 860 m. Variations in the limits of the three altitude
classes did not change the qualitative result. The map sheet
chosen to produce Figure 1 is representative of the Orbost Region.
Elsewhere in the State, warm temperate rainforest is limited
to the lowest elevational range and cool temperate rainforest
occupies a wider elevational range.
Fundamental research has been undertaken into the ecological dynamics
of Australian cool temperate rainforest including light attenuation
in the rainforest canopy (Olesen, 1992) and nutrient dynamics
in successional and climax rainforest (Adams et al. 1989,
Ellis and Pennington 1989). Autecological studies of primary
rainforest dominants have likewise concentrated on cool temperate
rainforest taxa including the regeneration ecology of Nothofagus
cunninghamii, Eucryphia lucida and Atherosperma
moschatum (Howard 1973 a,b, Hickey et al. 1982) and
the bioclimatic limits of N. cunninghamii (Busby 1986,
1987). In addition, the regeneration and drought and flood resistance
of two warm temperate rainforest species, Tristaniopsis laurina
and Acmena smithii, have been studied by Melick (1990 b,c,d).
Much of the ecological research on Australian cool temperate
rainforest has been undertaken in Tasmania, perhaps because of
its relative area (10% of that State's forests) and considerable
economic importance. In this review, some of the results from
ecological research in Tasmania's rainforests and sclerophyll
forests are extrapolated to the equivalent Victorian forests.
In Tasmania, forest with a eucalypt overstorey and a rainforest
understorey is termed mixed forest (Gilbert 1959). It is outside
the strict definition of rainforest adopted by CNR (CFL 1987)
because of the structure and composition of the overstorey. Radic
et al. (1985) defined mixed forest on the Errinundra Plateau
as 'Open forest III and IV with closed forest; cover of the tallest
stratum 10-50%.' That is, mixed forest was considered to be forest
with eucalypt crown cover between 10% and 50%, and with a closed
forest understorey made up of rainforest dominants. Currently,
this forest type is not classified separately in Victoria, but
is subsumed under various sclerophyll forest types. The distribution
of this forest type in the O'Shannassy River Catchment in relation
to mature and secondary rainforest is shown in Fig. 2. This example
may not be representative of mixed forest or rainforest elsewhere
because it is one the few areas not burned in the 1939 wildfires
and it includes a substantial proportion of old wet forest in
the Central Highlands. While this example is from a catchment
that will not be harvested, it shows that stands of secondary
rainforest do not always follow the boundaries of mature rainforest.
In the absence of fire for long periods, secondary rainforest
and mixed forest stands may be very extensive.
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