Download remnant vegetation ~ values and threats

Chapter 2
remnant vegetation ~ values and threats
Jann Williams
School of Environmental and Information Sciences,
Charles Sturt University, Albury, NSW.
I
NTRODUCTION
Because remnants on private land contain much of the
biodiversity outside these reserves, their ongoing
management is critical for biodiversity conservation.
However, while remnant vegetation has inherent and
precious biodiversity value, it also has qualities that
are particularly relevant to the sustainability of
agriculture. Benefits of remnant vegetation include the
prevention and amelioration of dryland salinity,
minimisation of soil loss, habitat for native wildlife
(important in natural pest control), the provision of
shade and shelter for crops, pasture and stock,
aesthetic values, the opportunity to maintain genetic
diversity and to take advantage of a cheap regeneration
method, via self-regeneration. Remnant health is also
increasingly being acknowledged as one of the
indicators of sustainable agriculture.
(G. Johnson)
The South West Slopes of New South Wales is an
agricultural area of national significance and the value
of the land for cropping and grazing has led to
widespread clearing of the native vegetation. This has
created patches of remnant vegetation around which
most or all of the original vegetation has been removed
(see Figure 1). Much of this native vegetation is
located on steeper, rocky or infertile soils and some on
travelling stock routes and railway lines. Few
examples exist, however, of the vegetation types which
once occurred on more fertile and accessible areas.
Any remnants in these areas can be assumed to have
high conservation value, even if they are degraded.
The remnant vegetation in the South West Slopes has
many shapes, sizes and degrees of isolation. It
represents a number of vegetation associations and
occurs on a range of soil and ownership types. For
example, State Forests manage remnant forests and
woodlands which can cover an area of several
thousand hectares. Typically however, remnants are
small, including most of the conservation reserves in
the region. These reserves do not adequately sample
the range of biodiversity in the South West Slopes. For
example, plant communities occurring on particular
geological types, or grassy White Box (Eucalyptus
albens) woodlands are not adequately represented in
reserves.
Figure 1.
Remnant vegetation is typically found along
roadsides or travelling stock routes.
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Prevention and amelioration of dryland salinity
Deep rooted, perennial native vegetation helps slow
the development of surface salinity by utilising ground
water. This water may otherwise contribute to rising
water tables, waterlogging and accumulation of salt on
the surface.
Minimising soil loss
Soil erosion removes valuable top soil and nutrients
which causes pollution, salinisation, siltation and algal
blooms in water bodies. The only effective way to
reduce soil erosion is to maintain groundcover and
keep surface run-off to a minimum by ensuring the soil
structure is good enough to allow good infiltration of
water into the soil. Retaining remnants on farms,
particularly on steeper areas and along water courses,
can help minimise soil loss and erosion and therefore
contribute to farm productivity.
Biodiversity conservation
As already noted, remnant vegetation often represents
the best remaining examples of particular ecosystems.
Therefore, remnants are particularly important in the
conservation of biodiversity and ecological processes
in the South West Slopes.
Habitat for native wildlife
Remnant vegetation provides important habitat for
local native wildlife including insects, birds,
mammals, lizards and frogs. Hollows, which generally
do not start forming until a tree is at least 100 years
old, provide essential sites for nesting and shelter for
animals such as birds, mammals and bats (see Figure
2). Due to their size, mature trees also provide more
food resources than younger trees. Essential habitat is
provided for insects, reptiles, frogs and birds by
branches, twigs and leaves that fall to the ground
(litter). Litter also reduces erosion and maintains soil
fertility as it breaks down.
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Natural pest control
Remnant vegetation may attract native wildlife that
prey upon pasture, tree and crop insect pests, thus
providing an alternative to pesticides, which are often
harmful to useful species. Wildlife also assist in
keeping remnant vegetation healthy, by preying on
pests and by carrying predatory parasites and diseases
that also reduce pest numbers. As the range and
quantity of wildlife that preys on pests increases with
habitat diversity, natural pest control is enhanced if
there is a diverse habitat, with understorey being
particularly important (see Practical Information Note
— Natural Pest Control).
Shade and shelter
Remnant native vegetation can provide protection for
plants and animals from wind, cold and heat stress. It
can shelter stock which reduces lamb and sheep offshears mortality and improves growth rate. It can
shade stock, and reduce heat stress, leading to higher
weight gains and improved fertility in sheep. Remnant
vegetation can protect newborn sheep and cattle by
sheltering them from wind and sun and reduces water
Figure 2.
Hollows in
old trees
are nesting
sites for
many
native
birds.
(G. Johnson)
VALUES OF REMNANT VEGETATION
Chapter 2
loss from crops and pastures by providing shade. The
extent of the shelter partially depends on the height of
the trees, with mature trees providing more benefits
than recently planted trees. Enhanced shade and
shelter is also provided if the vegetation is growing in
clumps or in strips (common along roadsides) and
includes understorey plants such as grasses and shrubs.
Economic values
There are potentially many sources of direct income
from remnant vegetation. These include grazing,
browse and fodder; tourism, education and amenity;
specialty timbers, craftwood and fuelwood; native
seed; cut flowers, foliage and fruits; tannins, resins and
essential oils; bush foods and honey (see Chapter 12.
The economic use of remnant vegetation, for details).
Aesthetic and other values
Remnants have aesthetic, educational, recreational and
scientific values. They contribute an additional visual
dimension to human-modified landscapes because
they retain a relatively natural appearance. They are
also valuable indicators of what the landscape used to
be like. Mature trees, which can be up to 400 or 500
years old, are particularly valued for their beauty and
contribution to wildlife habitat. Trees planted today
will take at least 100 years to attain a similar
dimension in the landscape. Because remnants are
generally dispersed across the landscape, they are
relatively accessible to local communities. They are
also suited for research and interpretation. Taken
together, these characteristics create a significant
educational tool.
Maintenance of genetic diversity
Remnant vegetation, whether it is a lone paddock tree
or a patch of bushland, provides a source of plant and
animal genetic material that can generally be enhanced
by encouraging regeneration. This is particularly
important as remnants are often the best remaining
examples of once-intact ecosystems. Unfortunately,
most remnant vegetation is either disappearing
through continued clearing, or degrading more slowly
due to factors such as livestock grazing, weed invasion
and rural dieback. Once lost, these complex systems
are extremely difficult, if not impossible, to recreate.
Indicators of sustainable agriculture
It has been proposed by the Commonwealth/State
Standing Committee on Agriculture and Resource
Management that the total area and health and degree
of fragmentation of native vegetation (remnant and
replaced) may be a useful indicator of sustainability in
broadacre cropping areas. The contribution of native
vegetation will depend on the health and degree of
fragmentation (i.e. corridors or isolated patches of
vegetation), the plant species involved, fauna habitat
provided, soils, hydrology and topography.
THREATS TO REMNANT VEGETATION
Most remnants have been modified by activities such
as grazing, weed infestation, forestry, fire wood
collection, herbicide, pesticide and nutrient drift, and
altered fire regimes. Rural dieback is also a major
factor in the decline of remnants on farms (see
Practical Information Note — Rural Dieback). These
activities threaten not only existing vegetation, but also
can have a major impact on the regeneration of native
species, and hence the long-term viability of remnants.
Altered disturbance regimes (fire, impacts of
domestic stock, water and nutrient transfers)
Fragmentation of natural vegetation into small patches
generally leads to changes in the types of disturbances
that occurred prior to clearing. This has the potential to
alter the long-term functioning of the communities that
remain. Alterations to the types of disturbance in
remnants include changes in the frequency, timing and
intensity of fires, or changes in grazing pressures.
Additional disturbance may arise from new transfers
of nutrients, pesticides and water between natural
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Chapter 2
Domestic stock do not only cause changes to the way
native vegetation is grazed. They break down the soil
structure by trampling, increase soil nutrient levels
through their waste products (which appears to make
trees prone to insect predation), ringbark trees (a
particular problem with stringybarks) and introduce
exotic seeds via faeces or body surfaces.
Pest plants and animals
Invasion of weed species into remnant vegetation is of
particular concern. Once established, it is likely that
weeds will have a detrimental effect on the vegetation
by impeding regeneration of native species, through
their impact on the availability of
nutrients, water and light and potential
alterations to the fire regime through
changes in fuel characteristics (see
Chapter 6. Environmental weeds). Pest
animals such as foxes and cats can also
have a detrimental impact on some of
the fauna that inhabit remnants.
Rural dieback
Clearance of native vegetation, mainly
by heavy machinery and herbicides, is a
continuing threat to remnants. A more
insidious loss of natural ecosystems on
farms, however, results from rural
dieback. Rural dieback is the premature
and relatively rapid decline and death of
native trees on farms, apparently as a consequence of
interacting environmental stresses (see Practical
Information Note — Rural Dieback). Deliberate tree
clearing and the intensification of land use associated
with it are pivotal factors in the development of rural
dieback. Remnants with dieback are usually small and
lack diversity of vegetation structure, numbers of plant
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species, age classes and fauna. The pressure from
grazing by insects is usually severe and sustained,
leading to sparse crowns and considerable epicormic
growth, and tree disorder and death is common (see
Practical Information Note — Insects and Tree Decline).
Lack of regeneration of native species
All causes of tree mortality such as ageing, disease,
drought, flooding, exposure to extreme weather, insect
damage, lightning, hares and rabbits must be viewed in
relation to the regeneration of new individuals. The
increase in grazing intensity and trampling by cattle
and sheep has reduced, and in many cases eliminated,
the natural replacement of trees and shrubs (see Figure
3). This is because livestock have not been fenced out
of bushland remnants on most farms. Grazing by pest
animals such as goats can also be a problem in
remnants on outcrops and in the ranges.
(F. Stelling)
vegetation and adjacent agricultural land. These
transfers are likely to affect the dynamics of the
remnants. In particular weed species may be favoured
by greater nutrient availability.
Figure 3.
Typical isolated paddock trees not regenerating and
lacking associated understorey.
Chapter 2
THE FUTURE
While the conservation and management of remnant
vegetation is challenging, with strategic planning,
sound technical advice and the enthusiasm and
commitment of land managers and local communities,
the long-term future of remnant vegetation in the
South West Slopes is looking much brighter.
REFERENCES AND
FURTHER READING
Bos, D. & Lockwood, M. 1996, Flora, fauna and other
features of the South West Slopes biogeographic
region, NSW, Johnstone Centre Report No. 59, Charles
Sturt University, Albury, NSW.
Davidson, R.L. 1995, ‘Farmers as conservators of a
sustainable production base’, in R.A. Bradstock, T.D.
Auld, D.A. Keith, R.T. Kingsford, D. Lunney and D.P.
Sivertsen (eds), Conserving biodiversity: threats and
solutions, Surrey Beatty and Sons, Chipping Norton.
Department of Land and Water Conservation 1995,
Native vegetation protection and management in NSW,
Information paper, Department of Land and Water
Conservation, Sydney.
Norris, E.H. & Thomas, J. 1991, ‘Vegetation on rocky
outcrops and ranges in central and south-eastern New
South Wales’, Cunninghamia, vol. 2, pp. 411-41.
Morgan, G. & Terrey, J. 1992, Nature conservation in
western New South Wales, National Parks Association
of NSW, Sydney.
Rural Industries and Research Development
Corporation (RIRDC) 1997, Sustainability indicators
for
agriculture:
introductory
guide
to
regional/national and on-farm indicators, RIRDC
Publication No. 97/72, RIRDC, Canberra.
Saunders, D.A., Arnold, G.W., Burbidge, A.A., &
Hopkins, A.J.M. (eds) 1987, Nature conservation: the
role of remnants of native vegetation, Surrey Beatty &
Sons, Chipping Norton.
Stelling, F. 1994, Revegetation guide for Northeastern Victoria, Department of Conservation and
Natural Resources, Victoria.
Yates, C.J. & Hobbs, R.J. 1997, ‘Temperate eucalypt
woodlands: a review of their status, processes
threatening their persistence and techniques for
restoration’, Australian Journal of Botany, vol. 45, pp.
949-73.
Hale, P. & Lamb, D. 1997, Conservation outside
nature reserves, Centre for Conservation Biology,
University of Queensland.
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