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I. Introduction 2. DEFINITION OF RAINFOREST
While various definitions of rainforest exist (cf., Webb 1968,
Dale et al. 1980, Gell and Mercer 1992, Cameron 1992, Busby
and Brown in press), this report will use the working definition
of rainforest adopted by the Government, namely: 'rainforests
are defined ecologically as closed (>70 percent projective
foliage cover) broad-leaved forest vegetation with a continuous
rainforest tree canopy of variable height, and with a characteristic
diversity of species and life forms. Rainforest canopy species
are defined as shade-tolerant tree species which are able to establish
below an undisturbed canopy, or in small canopy gaps resulting
from locally recurring minor disturbances, such as isolated windthrow
or lightning strike, which are part of the rainforest ecosystem.
Such species are not dependent on fire for their regeneration'
(Department of Conservation, Forests and Lands (CFL) 1987, p.3,
Gell and Mercer 1992). However, the ecological dynamics of vegetation
associations included within broader definitions of rainforest
(Webb 1968, Dale et al. 1980) and their implications for
the protection of rainforest will be considered.
The working definition of rainforest includes forest with scattered
emergent eucalypts. When trees die, are wind thrown or disturbed
by fire, there may be 'the opportunity for a partial eucalypt
overstorey to be maintained' (CFL 1987, p. 2). The threshold
of eucalypt canopy cover that distinguishes rainforest from sclerophyll
forest has not been defined in Victorian Government policy statements.
Applications have suggested the use of threshold canopy covers
for eucalypts ranging from 10% (eg., Radic et al. 1985) to 50%
(eg., CNR, 1994) below which vegetation is classified as rainforest.
The exact definition is likely to be different for different
regions and vegetation types.
From an ecological perspective, the use of the canopy cover of
a single genus (Eucalyptus) to delimit rainforest is inappropriate
unless the abundance of the genus correlates perfectly, or at
least very closely, with all of the other features that characterise
rainforest. If the intention of the use of a single species to
discriminate between communities within wood utilisation areas
is solely to remove any ambiguity in the process of delineation
of community types, it is an effective, if rather arbitrary, classification
tool. From a practical perspective, the use of eucalypts to delimit
rainforest is simple to apply in the field.
The Code of Forest Practice protection measures that are applied
within wood utilisation areas (see below) make use of the idea
that the core zone of rainforest is afforded complete protection,
and that the ecotone between rainforest and sclerophyll forest
is largely protected within buffers. The assumption is made that
these buffers provide sufficient amelioration of physical and
ecological processes that the long term chances of persistence
of rainforest stands are not adversely affected. The utility
of this assumption for the protection of seral vegetation associated
with rainforest depends on the width of the ecotone separating
rainforest from sclerophyll forest.
In areas with less than a threshold eucalypt canopy cover, rainforest
is recognised as forest where the highest proportion of foliage
cover is contributed by Acmena smithii (lilly-pilly), Acronychia
oblongifolia (yellow wood), Atherospermum moschatum
(sassafras), Cissus hypoglauca (jungle grape), Eleaocarpus
holopetalus (black oliveberry), Eucryphia moorei (eastern
leatherwood), Nothofagus cunninghamii (myrtle beech), Pittosporum
undulatum (sweet pittosporum), Rapanea howittiana (mutton-wood)
and/or Tristaniopsis laurina (kanooka) (CFL, 1987). Other
important species include Acacia melanoxylon (blackwood),
Elaeocarpus reticulatus (blue olive-berry) and Pittosporum
bicolor (banyalla). Government policy excludes timber harvesting
from Victoria's rainforest, as defined above. None of these species,
on their own, could necessarily be used to identify rainforest,
although it is recognised that some rainforest types are dominated
by a single canopy species, for example, Tristaniopsis laurina.
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