Byron Flora and Fauna Study 1999 - Byron Shire Council

BYRON FLORA AND FAUNA STUDY, 1999
Buchanan (1989) advises on the rehabilitation of Australian landscapes generally and is a useful reference
for heaths and sclerophyll and other coastal communities.
7.2 VEGETATION CONNECTIVITY AND FRAGMENTATION
The vegetation map (Map 3) demonstrates the severance of vegetation connections and fragmentation of
vegetation patches in Byron Shire at a number of scales. A pattern of dissection of large vegetation blocks in
formerly heavily vegetated areas is apparent with the reduction of already isolated patches in other areas to
widely scattered smaller patches of remnant and regrowth vegetation. Corridors and linkages which previously
allowed fauna movements and plant gene flow have been severed.
A general severance of the hinterland forests from the coastal vegetation systems has resulted from largescale
clearing of the coastal plain, basalt plateau and foothill forests. Some connections remain although
most are tenuous with the most substantial existing in the Marshalls Ridges area. Other connections consist
of a series of ‘islands’ of vegetation. The narrow coastal corridor is interrupted by settlements and clearings
for agriculture and development. Much riparian vegetation in the Shire is cleared completely or partially, or
remains as narrow degraded strips. These riparian zones frequently provide important strips of vegetation
that facilitate fauna movement and plant gene flow.
The process of fragmentation sets in train a series of ecological processes which change the structure and
species composition of the vegetation and ultimately result in degradation and the loss of species from an
ecosystem. Fragmentation of vegetation results in an overall reduction in area (Section 7.1), an increase in
the edge/unit area value, and indirect effects on species composition, such as losses of species diversity,
resulting from disruption of biotic interactions. The extent of the effects varies with remnant size and
distance from neighbouring forest, time since isolation and the nature of the matrix environment (Laurance
1991a).
Edges of forest remnants are subject to physical damage and the effects of increased temperature and drying
or salt-laden winds. Alteration to the physical environment leads in turn to changes in species composition
and vegetation structure. Early successional vegetation which invariably includes weed species replaces
species of later successional stages. The new edges increase predation pressures generally and nest parasitism
among birds and are favoured habitat for species such as the aggressive Noisy Miner. Non-forest species are
able to exploit the habitat (Janzen 1983). Edge effects may penetrate so far into smaller remnants that little
or no core forest remains (Laurance 1991b).
The disruption of faunal movement corridors can adversely affect individual species directly, and can have
indirect effects on plant species which depend on fauna for pollination and seed dispersal, resulting in
modifications to whole ecosystems. A pre-existing habitat matrix may be truncated so that species which
require missing adjacent habitats on a seasonal basis will be unable to persist. Many fauna species are
nomadic or migratory and the disruption of movements may have significant local effects. For example in
Byron Shire the movement of hinterland species to the coast to exploit winter food resources is a common
pattern. In the long term, genetic problems can be expected in isolated populations.
The disruption of pollination and seed dispersal will affect the regeneration of plant species. Indirect effects
of fragmentation may flow through one or more trophic levels in the system, so that a perturbation may
affect organisms which seem far removed, both ecologically and taxonomically, from the subject of the
perturbation. For instance, the removal of seed predators from some of the Big Scrub remnants has resulted
in excessive regeneration of the Black Bean (Lott and Duggin 1993), which may eliminate other plant
species through competition.
Species loss resulting from fragmentation has been best documented for fauna species, particularly specialists
and those requiring large home ranges or territories. Rainforest mammals and birds are no longer fully
represented in all the Big Scrub remnants (Lott and Duggin 1993). Loss of plant species is also likely, but
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