River Red Gum Ecosystems
January 2014
Riverina Environmental Education Centre
Table of Contents
1. Location
2. Landform
3. Soils
4. Climate
5. Flooding
6. Plant communities
7. Understorey survey
8. Distribution and abundance - plants
9. Distribution and abundance - animals
10. Capture-recapture
11. Adaptations
12. Predator-prey
13. Allelopathy
14. Flow of energy
15. Food webs
16. Cycling of matter
17. Human impacts
18. Forest Management
19. Ecosystem management
20. Management scenario
Articles
1. CSIRO River Red Gum Forests 12 page pdf
2. Legislation and new national parks 2010 pdf
3. Blackwater events
(Murray-Darling Freshwater Res. Ctr. 3 page pdf)
Animal case study:
3. Gumleaf Skeletoniser pdf
4. Psyllids pdf
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1. Location
River red gum trees are the most widely distributed tree in Australia but
it is only along the Lachlan, Murrumbidgee and Murray Rivers and their
major tributaries that they form dense forests. Major forests occur in the
area of Deniliquin, Tocumwal and Echuca and display as darker colours in the satellite image
below.
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2. Abiotic features
Landform
Red gum forests grow on floodplains adjacent to rivers.
Use the photo below to describe the major landform. What minor landform features are
present?
Runners
The forests have natural channels (runners), which help distribute floodwaters through the
forest. Water from the river enters the channels and flows into the forest. Runners hold water
over long periods providing habitat for aquatic and other organisms.
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3. Abiotic features
Soils
Floodplain soils form from alluvium (soil parent material) deposited during floods. Beside
the floodplain at Wagga Wagga are relict sand dunes formed during the last glacial period.
Very different soils have formed on the floodplain and the sand dunes. Two important soil
characteristics are texture, the proportion of sand, silt and clay size particles and soil acidity
(pH).
Soil Texture Test: crush a handful of soil, moisten it and knead it in the hand. Role it
between the palms to form a ball. If it does not it is a sand. If it forms a ball which can then
be rolled into a rod (pencil shape) it is a loam. If the pencil can be turned into a circle it is a
clay.
What texture is the floodplain soil?
pH is a measure of acidity. Crush a sample of soil (1/2 teaspoon) place 3 drops of universal
indicator (Raupach) then sprinkle with barium sulphate and wait 5 minutes for the colour to
develop then check against the colour card. Above 7 is alkaline. Below 7 is acid and 7 is
neutral.
What is the pH of the two samples here?
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4. Abiotic features
Climate
The forests require over 1100 mm of
moisture to remain healthy, however, the
Wagga Wagga, Corowa and Deniliquin
areas have a very low rainfall, the rest of
the water needs of the forests is provided
by the floods caused by snow melt in
winter and spring.
The Snowy Mountains are part of the
water catchment of the major rivers of the
Murray, Murrumbidgee and Lachlan
where river red gum forests grow. The
winter spring floods of these rivers,
resulting from the climate in the mountains, provide much of the water these forests need to
survive.
Rainfall (median
mm)
Charlotte's Pass
(Mt. Kosciuszko)
J
F
M
A
M
J
J
A
S
O
N
D
148 135 150 182 207 212 215 242 213 267 213 166
Berry Jerry Forest
(Wagga Wagga)
44
39
43
45
54
43
52
53
52
65
42
36
Barmah Forest
(Deniliquin)
15
17
20
25
34
39
31
34
33
33
20
19
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5. Abiotic features
Flood Cycle
River red gum forests are only found on the floodplains of the Murray, Murrumbidgee,
Lachlan Rivers and their tributaries. Floods supply moisture for the trees, they create the
floodplain landform, deposit alluvium from which the soils form and are important for the
breeding cycles of native fish and water birds.
What would be the consequences if the floods ceased?
The graph shows the flow of the
Murray River to South Australia,
1902 to 1987 in GL/month
(a gigalitre is one thousand million
litres).
Under natural conditions, floods
occurred, on average, every 1.7 years
for two to three months during spring
when the snow melted in the Snowy
Mountains.
Graph courtesy Murray-Darling
Basin Commission
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6. Biotic: plant communities
A number of plant species usually live in the same area because they are adapted to survive
similar environmental conditions. The following characteristics can be used to describe plant
communities.
Species diversity/Biodiversity: the number of different species of plants. How many types
of tree are found in most river red gum forests?
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What is the "limiting factor", the factor that stops other types of trees growing?
Structure is the number of height layers present of tall trees and understorey plants. River
red gum trees form even aged stands. A good spring flood followed by a mild summer results
in good germination and seedling survival resulting in stands of trees of the same age and
approximate height.
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Describe the structure in the photo below.
Form is the shape of the plants. The main forms are: trees, shrubs, grasses, herbs, moss and
lichen.
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Which forms are present in the photo below and which major form is missing?
Dominance refers to a species which controls the conditions under which other plants live.
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Explain why the river red gum tree is the dominant tree in the photo below.
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7. Understorey survey
Biologists surveyed the Barmah Forest (28900ha) near Deniliquin. They systematically
sampled the forest using 15 metre square quadrats spaced on a grid every 300 metres. They
found over 400 species of plants, most of which were herbs. 30% of species were introduced.
Below are some of the more common herbs and other understorey plants found in river red
gum forests. The red squares are 1m2 random quadrats. We would normally only count plants
with their root system within the quadrat. In this simulation count all plants within or
touching the sides.
Compare the species diversity for the whole area of the diagram:
a. determined by using the three random quadrats;
b. determined by doing a total count of the area.
How would you improve the random quadrat method so you recorded all plant species in the
study area?
How would you change your investigation methods to take into account plants which are
seasonal, with above ground parts only visible in some seasons?
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8. Distribution and abundance
New South Wales State Forests allows grazing leases with it's forests and cattle selectively
graze native herbs.
Scenario
There have been several reports that few swamp daisies have been seen in recent years. You
are part of a team asked to investigate the distribution and abundance of swamp daisies and
prepare a management plan. You decide to see if swamp daisies grow in all parts of the forest
or have specific micro habitats which need to be protected.
You make 10 random transect/quadrat combinations starting at and at 90 degrees to runners.
The transects are twenty metres long with five, 1m2 quadrats spaced at 5 metre intervals.
Below are your results for one transect. Each flower in a quadrat represents 10 plants.
Quadrat
Distance
1
5
10
15
20
Temp.(0C)
24.0
26.4
27.7
36.6
32.0
Humidity
(RH)
32.9
32.5
31.7
30.4
28.6
Light (lux)
2600
6000
5800
6800
9500
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Describe the distribution and abundance of swamp daisies using the five quadrats
above and the abiotic factors you have measured.
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Give possible reasons for the distribution and abundance.
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Describe tests/experiments you could carry out to determine which of the above
parameters is the "limiting factor"
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What other factors could determine the distribution of swamp daisies?
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9. Distribution and abundance of animals
Biologists with the Forests Commission of Victoria surveyed the Barmah Forest with the
following results.
Mammals
They used folding aluminium traps, wire cage traps, mist nets for bats and made observations
of diggings, scats and tracks and direct observation with spotlights at night to survey
populations. Between 20 and 50 traps were set at each site for one to three nights in five
study areas. The areas were trapped three times each in a year to study seasonal changes.
Species trapped included yellow footed antechinus, house
mice, brushtailed possums, ring-tailed possums and sugar
gliders.
11 species of bats were caught.
Photos: Lesser Long-eared bat and an antechinus
trapped during a mammal survey. Photos courtesy C
Dunstan, DLWC
Daylight observations included eastern grey kangaroos,
brumbies, flying foxes, hares, rabbits and foxes.
The most commonly observed mammals during spotlight surveys
were brush and ring-tailed possums, kangaroos and horses.
268 predator scats were collected, the majority from foxes and
cats. Microscopic analysis of hair and other remains enabled 278
prey items to be identified including 13 different mammals
including brush and ring-tailed possums, sugar gliders and
antechinus.
Birds
Birds were counted by direct observation. It was found numbers of water-birds changed
rapidly with changes to the distribution of aquatic habitats as
flood waters came and went.
201 species of birds were observed. These included:
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water-birds such as ibis, pelicans, grebes, cormorants,
herons, egrets, spoonbills
waterfowl such as grey teals, wood ducks, hardheads,
manned ducks
birds of prey - wedge-tailed eagle, harriers, goshawks
and kites
parrots - superb parrot, budgerigar, crimson rosella
tree birds - choughs, mudlarks, woodswallow, magpie,
raven, honeyeaters
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10. Capture – recapture
To estimate a population of animals we can use the Peterson Capture/Recapture Method
based on two sampling periods. At time 1, animals are captured, marked and released. At
time 2, animals are recaptured and checked for marks. The traps were set in a square area
with 5 metres sides.
Our example uses cockroaches caught in Berry Jerry State Forest.
Abundance = number marked Time 1 x number captured Time 2 divided by number marked
in recapture Time 2.
Abundance of cockroaches = 18 x 45 divided by 13 = approximately 62 cockroaches in the
area surveyed.
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To survey beetles on river red gum foliage, a sheet was placed below the tree and the lower
branches were shaken. Fallen beetles were then collected, marked and released. The process
was repeated 24 hours later.
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How many beetles were captured, marked and released at Time 1?
How many beetles, both marked and unmarked were captured at Time 2?
Use this information to calculate the beetle population of the branches surveyed?
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11. Adaptations
River red gum tree: basic adaptations as for other trees
Basic adaptations are determined by the trees needs as a photosynthetic organism which
requires light, carbon dioxide, water, oxygen for respiration and inorganic ions such as
phosphorus, calcium etc.
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Leaves have evolved as light capturing organs and as factories in which
photosynthesis occurs.
Trunks have evolved to hold the leaves above other plants so they are not shaded and
capture more light.
Branches have evolved so the leaves are held out in the crown of the tree and do not
shade each other.
A well developed root system has evolved to support the tree and collect water and
nutrients.
Adaptations specific to river red gum trees
River red gums are able to survive in a very harsh environment, they are the only tree which
has evolved to survive long periods of flooding.
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It is an opportunistic water user, and has the ability to transpire water whenever it
becomes available. At these times growth may double but in dry times it may show
very little growth.
Internal oxygen transport and the ability to take oxygen in through the trunk when the
roots are flooded and still need oxygen to respire.
Development of floating root masses to extract oxygen from the air during floods.
Specialised root tissue to extract water from sandy lenses in the clay soil during dry
times.
Very deep root system to extract groundwater from the soil in summer.
Seedlings have a very large root to shoot ratio of 4:1 which allows them to reach the
watertable as it falls in summer.
Large seed drop in spring which coincides with the floods and good conditions for
germination prior to the hot summer.
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Brush tailed possum adaptations
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Nests in tree hollows for
protection from floods.
Arboreal which helps during
floods.
Strong, sharp claws for climbing.
Opposable first toe on the hind
foot for climbing.
Prehensile tail for holding on to
branches, some possums have
better tails for this, but the
brushtails' still works.
It mainly eats leaves.
Fur for warmth. Legs for climbing
Territorial to protect food
supplies.
Large eyes for nocturnal habit.
Photo courtesy C. Dunstan, DIPNR
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12. Predator prey associations
The gum leaf skeletoniser is a moth whose larvae defoliated
more than 40 000 hectares of river red gum forest in the Murray
and Goulburn Valleys in 1975. The 1975 outbreak followed
earlier ones at intervals every ten years since they were forest
recorded in 1933.
The moths are poor fliers so eggs
are laid on low foliage. The eggs
are grouped in masses called egg rafts. The young feed on the
leaf's photosynthetic tissue, leaving the veins and midrib as a
skeleton. The mature larvae spin a cocoon at the base of the tree
in leaf litter. Moths emerge and live for about ten days. When
the larvae moult, the old head skin remains, forming a hat.
The main predator is a fungus,
Aspergillus, which controls the
population. The fungus thrives in humid
conditions following flooding. If flooding
does not occur at a time when larvae are
close to the ground, between March and
June and October and January, the
population will not be controlled. This
greatly increases the potential of a
population explosion of the next
generation. There are two generations
each year.
Based on Defoliation of River Red Gums by Gum Leaf Skeletoniser, 1986, Research and
Development Note, Dept. Conservation, Forests and Lands Victoria.
Foxes and feral cats are important predators in river red gum forests. The following
mammals were identified in fox and cat scats in a study of Barmah Forest (river red gum):
sugar gliders, yellow-footed antechinus, ringtail and brushtailed possums. Local residents
also reported that bandicoots, stick-nest rats and bettongs were once present. The decline in
mammals appears to have coincided with European settlement and consequent loss of habitat
from grazing and the introduction of foxes and cats.
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13. Allelopathy, parasitism, mutualism and commensualism
Allelopathy: river red
gum understorey's have
a low diversity of herbs.
Red gum foliage
contains terpenes and
phenolic acids which
accumulate in the soil
and are toxic to other
plants. Without floods,
these toxins accumulate.
Parasitism: mistletoe
plants are found on red
gum trees on the edge of
forests. This plant obtains
water and nutrients by
growing into the tree's
xylem and phloem tissue.
Mistletoe then makes its
own food via
photosynthesis.
Mutualism: lichen
growing on bark is two
organisms, a fungi
which provides a
structure for the algae
to live in, while the
algae provides food for
the fungi via
photosynthesis. Both
organisms benefit.
Commensalism:
brushtailed
possums use
hollows in river
red gums for
nesting. There is
no harm to the tree
but hollows are
necessary for the
possum for shelter
and breeding.
With less flooding, river red gum phenolic acids build up in the soil, resulting in less
biodiversity in the understorey plants.
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14. Flow of energy
Food chains show the flow of energy from the sun to plant to herbivore to carnivore. There
are usually only 3 to 5 steps in a food chain because of the loss of energy along the way. If
we start with 1 000 000 units of solar energy striking a river red gum leaf, about 99% is lost
as heat back into the atmosphere. About 1% (10 000 units) is used in photosynthesis to
convert solar energy into chemical energy. Of this 9/10 is lost in plant respiration and in leaf
fall. Herbivores such as lerps eat the remaining 1/10 (1 000 units) but of this, again 9/10 is
lost by herbivores in respiration and faeces and so on for carnivores until there is only one
unit one energy left for the top carnivore.
Possible food chain of organisms in Berry Jerry State Forest
Producer: plant, river red
gum tree
Consumer:
Consumer: carnivore- huntsman Consumer: detritavoreherbivore- beetle spider
cockroach
If the red gum intercepts
1 000 000 units of energy
from the sun,
10000 units become plant
material,
9000 units fall as leaf litter.
1000 units of
leaf energy are
consumed by the
herbivores, of
this 900 units are
lost as litter in
faeces and in
respiration.
100 units of energy are
available to carnivores, of this
90 are lost as faeces and in
respiration.
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Detritavores obtain
energy from litter from
each of the earlier
stages, plants,
herbivores and
carnivores.
Pyramids
It is difficult to compare food chains and webs from one ecosystem to another because
species change. However if we ignore species and group organisms in pyramids according to
food habits (trophic levels), we can make some general comparisons between ecosystems.
A biomass pyramid is based on the dry weight of organisms at each level.
In a river red gum forest this could be 35 kg/m2 for Level 1 being the average dry weight of
trees per square metre of forest. The biomass of herbivores could be 50 grams/m2 and
carnivores, 5 grams/m2. (The figures given are estimates.)
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15. Food webs
Feeding relationships of
plants and animals are much
more complex than the food
chain example given. A
simple, linear food chain
interacts with many others
and is expressed
diagrammatically as a food
web. In the river red gum
ecosystem there appears to
be a number of food webs
depending on the season and
whether animals are active
at night or during the day.
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thornbill: small insect eating bird, hunts in foliage of trees
brown treecreeper: small insect eating bird, hunts on trunks and branches
scarlet robin: small insect eating bird, hunts in foliage of trees
goshawk: large bird, hunts small birds and mammals
magpie: large bird, hunts invertebrates in soil
sulphur-crested cockatoo: large bird, gathers seeds on ground
gumleaf skeletoniser: caterpillar feeds on foliage, moth feeds on
nectar
gum tree hoppers: small sap-sucking insect
psyllids: small sap-sucking insect, nymph has small shell on
leaves shown in the photo.
Night Food Web
Nocturnal animals, especially
mammals, hunt and forage at
night then rest through the
day.
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brushtailed possum:
eats leaves and
blossoms. Fall prey to
foxes as they come to
ground to move
between trees now
that there are fewer
trees with logging.
squirrel glider: small
possum feeding on
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beetles, caterpillars and nectar. Again, more predation by foxes as they come to
ground to move between trees because of logging.
boobook owl: preys on small vertebrates and large insects.
lesser long-eared bat: preys on insects.
yellow-footed antechinus: small marsupial which preys on insects and small mammals
such as mice.
fox: introduced predator which is possibly responsible for the disappearance of
medium size mammals from the forest such as the rufus bettong and the western
barred bandicoot.
Food web for flood waters
Nutrient rich floodwaters
result in population
explosions of microscopic
plants, phytoplankton, which
in turn are eaten by
microscopic animals,
zooplankton. This forms the
basis of a short term food
web which can sustain a lot
of predators (large biomass).
Flocks of water birds
migrate to the forests to
breed and feed.
Native fish also take
advantage of the conditions to breed, the floodplain being an ideal nursery for larval fish
which eat the zooplankton.
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purple spotted gudgeon: small endangered native fish
golden perch: grows into a large native fish.
phytoplankton: microscopic plants (algae)
zooplankton: microscopic animals such as copepods.
yellow-billed spoonbill: large water bird which feeds in shallow waters for aquatic
insects.
Pacific heron: large water bird which feeds in flood waters for frogs, small fish,
aquatic insects and yabbies.
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16. Cycling of matter
The diagram shows some of the flows of
matter and energy as indicated by the red
arrows. Apart from the normal cycling of
nutrients between soil and plants,
floodwaters import large amounts of
matter in the form of the flood waters
themselves, silt and clay are also
deposited during floods and nutrients such
as phosphorus are also imported, attached
to clay particles or in solution in the
water.
Cycling of important nutrients occurs
between the trees and the soil. Table 1 below shows figures for the cycling of some nutrients
in a different forest type but they give an idea as to the quantities involved. Before leaves die
and fall, the tree will remove up to half the nutrients back into the canopy to be used by new
growth. The remaining nutrients will be released back into the soil from the litter by fungi,
microbes and invertebrates. Some nutrients dissolve from the leaf into rainwater (leaching)
and enter the soil in the water.
Biomass to soil kg/ha/yr. Phosphorus (P) Calcium (Ca) Potassium (K)
Litter
Leaching from leaves
1.0
20
3.7
0
6
11.0
Not all energy and matter is passed
down the traditional food chain of plant,
herbivore, carnivore. River red gum
leaves live for about 2-3 years and in
that time only part of the leaf is eaten by
herbivores, the rest is eaten by
detritavores on the forest floor when the
leaf falls as litter.
Use the diagram at left to estimate the percentage of each of the 10 leaves eaten.
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17. Human impacts
The forests have evolved over tens of thousands of years to
survive the natural flooding regime of the major rivers.
Under natural conditions the rivers had major floods every
1.7 years for 2-3 months duration. The rivers and floods
formed the floodplains themselves, they deposited the
alluvium for the soil and they provided over half the water
needs of the trees. Without the floods the forests will die.
The other organisms also evolved to survive the natural
flood regime. Native fish depend on the floods for
spawning and the floodplains are a nursery for the juvenile
fish. Without floods, the adult female fish
re-absorb the eggs and do not spawn. The life cycle of
many water birds depends on the floods. The birds breed
when the warm flood waters provide lots of aquatic insect
to feed the young so their breeding cycle depends on the floods. Without floods, the chicks
die from starvation.
River regulation
The graph shows the large variability
in river flows from year-to-year and
between seasons. This was unsuitable
for irrigation farmers such as in the
Murrumbidgee Irrigation Area. They
require dependable supplies of water.
They also require water in summer
when the rivers were normally low.
Graph courtesy Murray-Darling
Basin Commission
The answer was to regulate rivers by
building large storage dams in their
headwaters such as Hume Reservoir at
Albury on the Murray River shown in
the photo with the Snowy Mountains in
the background. Once stored, the water
could be released when required.
Photo courtesy Albury Wodonga Development Corp.
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The graph shows the change to the seasonal flow of water in the Murray below Albury. The
units are GL/month (one gigalitre is 1 thousand million litres).
Graph courtesy Murray-Darling Basin Commission
The graph at right shows how the volume of
water in the Murray River has changed at Euston
in South Australia. River regulation has resulted
in fewer floods of less duration and less depth
with the following impacts on the environment:
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The growth rate of trees in forests below
Hume Weir has decreased from 7 mm in
diameter to 4 mm per year.
Lower parts of some forests are now
permanently flooded and the trees have
drowned.
Waterbirds have adapted to the natural
flood cycle of 2-3 months for breeding purposes. It takes about 2 months from
courtship to when the chicks leave the nest. Now that the floods are of shorter
duration the adults abandon the nest because they cannot collect the food from the
floodwater to feed the chicks.
Waterbirds have very specific adaptations to collect food in water. Their legs, neck
and bill are a specific length to wade through shallow water to collect their food. If
the water is deeper or shallower they have difficulty doing this.
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Native fish species such as golden perch spawn in rising floodwaters. The juveniles
live on the floodplains which act as a fish nursery where there is a lot of food and
shelter. As the floodwaters recede after 2-3 months they enter the rivers.
Explain the impact of river regulation on natural ecosystems.
Photo: swan nest
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18. Management
Berry Jerry State Forest and three other forests became part of the newly formed
Murrumbidgee Valley National Park when it was formed in July 2010. Read the article on
this legislation.
This indicates a change in community values from one of timber production to that of
preservation. The community now values the biodiversity and preservation of the red gum
forests more than in the past.
Being a national park means the red gum forest is now protected by legislation and will be
managed according to a NPWS Plan of Management.
Prior to the Murrumbidgee Valley National Park, the area was managed by State Forests
according to the plan given below.
From the Management Plan for the Murrumbidgee Management Area (NSW State
Forests)
Management Objectives:
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To maintain the ecological viability of the natural red Gum floodplain ecosystems.
To maintain the area generally under forest vegetation so as to:
o Conserve soil and water values.
o Maintain a diversity of habitat suitable for the maintenance of wildlife,
particularly waterfowl.
o Maintain the floodplain as a breeding ground for native fish.
o Provide a flood buffer area. (Forests allow flood waters to infiltrate the soil
and reduce the size of the flood.)
o To supply sawlogs to industry at a rate designed to sustain a yield suitable
with the productive capacity of the area and consistent with the above
objectives.
o To supply other timber and forest products.
o To provide for the appropriate use by the public for recreation and education.
o To provide for grazing, apiculture and other forest uses.
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o
o
To maintain any rare or significant ecological, historical, floral, faunal or other
scientific or cultural values.
To maximise net financial returns from the forest.
State Forests are subdivided into Compartments usually between 200 and 500 ha in area.
Compartments are used for recording logging events, yields, floods, grazing etc.
Compartments are a tool to assist management, similar to a farmer having paddocks.
Plan for Timber Management (Murrumbidgee Management Area)
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The yield of River Red Gum sawlogs shall be limited to an average of 8 000 m3 per
year.
The yield of small logs called “thinnings” – Less than 40cm diameter) shall be limited
to 5 000 m3 per year.
No tree larger than 170cm diameter shall be felled specifically for wood production.
At least one and up to 5 suitable, mature trees with nesting hollows shall be retained
per hectare for wildlife habitat. All such trees within 20 m of any stream, 10 m of
lagoons and 60 m of the Murrumbidgee River shall be retained.
Trees showing signs of Aboriginal markings shall be retained, recorded and protected.
Trees identified as nesting trees of endangered fauna, specifically the Superb parrot,
shall be retained and protected.
Ramsar
The Convention on Wetlands of International Importance was the first modern
intergovernmental treaty between nations aiming to conserve natural resources. The signing
of the Convention took place in 1971 in the small Iranian town of Ramsar (since then, it has
taken the common name of the Ramsar Convention). Australia was the first nation to become
a Contracting Party to the Convention.
The Convention's broad aims are to halt the world-wide loss of wetlands and to conserve,
through wise use and management, those that remain. This requires international cooperation, policy making, capacity building and technology transfer.
Barmah Forest: Ramsar Site 14
The Barmah River Red Gum Forest consists of the section of the Murray River floodplain
within Victoria (i.e. south of the main river channel) near Barmah township. It is an area of
River Red Gum forest, subject to periodic inundation. The forest features a variety of
permanent and temporary wetlands, including lakes, swamps, lagoons and flooded forest.
These wetlands provide habitat for a large number of bird species.
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19. Ecosystem maintenance
Murray-Darling Basin Commission (Now MDBA)
and Catchment Management
In 1982 the River Murray Waters Agreement between
the states was amended to include water quality,
environmental and recreational issues as well as the
original water sharing role. In 1988 the MurrayDarling Basin Commission replaced the River Murray
Waters Agreement as community attitudes evolved
further to whole Catchment Management with the
increased understanding of the interrelationship
between land, water, vegetation and animals within
the catchments of the Murray, Darling and
Murrumbidgee Rivers and the need to manage them to
ensure sustainable use.
Environmental Flows
Following changing community attitudes to the environment, the NSW Department of
Infrastructure, Planning and Natural Resources now releases some water from the major
storage dams for the environment. In the past, rivers were regulated to supply irrigation
water, now regulation must also supply water for the maintenance of natural ecosystems,
particularly to increase the number of floods in river red gum forests. In July 1998, the first
'environmental flows' designed to mimic natural flows were released in the Murray,
Murrumbidgee and Lachlan Rivers.
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20. Management Scenario
Below is a map and cross-section of an area of forest following an ecological survey by you.
The area is due to be logged in the near future. You need to decide which areas of the forest
to protect for non-logging uses and which specific trees to protected as well. The criteria you
use have been reproduced after the diagrams.
Management Objectives:
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
To maintain the ecological viability of the natural Red Gum floodplain ecosystems.
To maintain the area generally under forest vegetation so as to:
o Conserve soil and water values.
o Maintain a diversity of habitat suitable for the maintenance of wildlife,
particularly waterfowl.
o Maintain the floodplain as a breeding ground for native fish.
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o
o
o
o
o
o
o
Provide a flood buffer area. (Forests allow flood waters to infiltrate the soil
and reduce the size of the flood.)
To supply sawlogs to industry at a rate designed to sustain a yield suitable
with the productive capacity of the area and consistent with the above
objectives.
To supply other timber and forest products.
To provide for the appropriate use by the public for recreation and education.
To provide for grazing, apiculture and other forest uses.
To maintain any rare or significant ecological, historical, floral, faunal or other
scientific or cultural values.
To maximise net financial returns from the forest.
State Forests are subdivided into Compartments usually between 200 and 500 ha in area.
Compartments are used for recording logging events, yields, floods, grazing etc.
Compartments are a tool to assist management, similar to a farmer having paddocks.
Plan for Timber Management (Murrumbidgee Management Area)
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The yield of River Red Gum sawlogs (diameter 50-160 cm) shall be limited to an
average of 8 000m 3 per year.
The yield of small logs (thinnings - < 40cm dia) shall be limited to 5 000m 3 per year.
No tree larger than 170cm dia shall be felled specifically for wood production.
At least one and up to 5 suitable, mature trees with nesting hollows shall be retained
per hectare for wildlife habitat. All such trees within 20 m of any stream, 10 m of
lagoons and 60 m of the Murrumbidgee River shall be retained.
Trees showing signs of Aboriginal markings shall be retained, recorded and protected.
Trees identified as nesting trees of endangered fauna, specifically the Superb parrot, shall be
retained and protected.
Tasks
1. What is the size of the forest included in the map in hectares (1 ha = 100m x 100m)?
2. Apart from logging, what values does this forest have? (What can we use it for?)
3. Trees with hollows.
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a. How many trees with hollows have been mapped?
b. How many must be kept per hectare?
c. How many can you legally remove?
4. The transect A-B is typical of the 10 transects you made to survey the forest. It was 300
metres long and 10 metres wide.
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
a. How many trees with a diameter of greater than 170 cm am I likely to have in the
whole forest?
b. How many trees suitable for sawlogs, dia 50 - 160 cm am I likely to have in the
forest?
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5. If you log all trees with a diameter of 50-160 cm:
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
a. What will eventually happen to the forest structure, the number of height layers in
the forest?
b. What will eventually happen to the habitat of animals which require mature trees
with trunks of greater than 170 cm dia.?
6. Draw a new map and cross-section to represent the forest after you have logged it. Keep in
mind your legal requirements with respect to logging trees near water courses.
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