Native Forest Management
Implications for grazing
By:
Bill Schulke,
Extension Officer (sustainable beef production)
DPI&F, Bundaberg
Acknowledgement:
EDGENetwork Grazing Land Management
1
Introduction
Grazing lands as functioning ecosystems
Grazing ecosystem
Everything you manage on your property (and a fair bit of what you can’t manage) is part of an
ecosystem. It includes: -
Soils (different quality soils, soil microbes and invertebrates)
-
Climate (Rainfall, variability, ENSO, drought)
-
Plants (grasses, herbage, trees, weeds)
-
Animals (livestock, native animals, feral animals)
-
Community and society in general (resource management perceptions and expectations)
-
And you (your need to make money and look after your land)
How efficiently this ecosystem converts sunlight and rainfall (through photosynthesis) into kilograms of
beef, is partly due to how productive your land is (its inherent fertility), and partly due to three
“gateways”; Land Condition, Pasture Utilisation and Feed Conversion Efficiency (see diagram).
Diagram 1. 3 Gateways model for grazing land management
Land condition
Land in poor condition will grow less than half the useful forage (given the same amount of rainfall) as
when it is in good condition. Land is in good condition when it has a good coverage of 3P grasses
(Palatable, Productive and Perennial), has few weeds, shows little sign of soil erosion or scalding and the
woody weeds are in check.
Land that only grows half of its forage potential is not very efficient at converting sunlight and rainfall
into forage, and hence, beef. It is probably not giving you a very good return on investment either.
Land condition can be maintained or improved through: 2
-
effective grazing management (safe utilisation rates, grazing systems, pasture spelling)
-
strategic use of fire
-
sown pasture development
-
woody regrowth control
-
weed management
Pasture Utilisation
The proportion of annual forage growth that is eaten by livestock is called the utilisation rate. A low
utilisation rate means that the conversion from forage to beef is inefficient. A high utilisation rate may
lead to short-term increases in animal production per hectare, but does so at the expense of individual
animal performance. Continual high utilisation rates over several years will lead to a decrease in land
condition and a consequent reduction in forage growth.
For native pastures in southeast Queensland, utilisation rates of between 20 and 30 % are considered to be
sustainable. Sown pastures can be sustainably utilised at slightly higher rates of 30 to 40%.
The forage that is not eaten by livestock is not wasted. It plays a very important role in providing soil
microbes (the unseen workers in a grazing ecosystem) with a source of energy and nutrients and provides
ground cover that protects the soil surface from the damaging effects of sun, wind and rain.
The utilisation gateway is managed by matching forage availability to forage demand and by setting or
adjusting stock numbers accordingly. Part of this equation includes allowing for other grazers (feral and
native animals, termites), and ground cover. The aim is to always come out of a dry season (including a
drought) with stubble on the ground.
Infrastructure (fencing and watering points), grazing systems and/or fire are all used to regulate when and
where cattle graze.
Feed conversion efficiency
Feed conversion efficiency is a measure of how efficiently a beast converts forage into beef (or milk
production). The class of animal and its genetics play a role but the import factor is the quality of the
forage eaten.
Forage quality varies between forage species. Leafy grasses, such as the 3P grasses, are more digestible
and higher in energy than stemmy grasses; legumes are higher in protein than grasses. Within a grass
tussock there are differences too; leaf is better quality forage than stem.
The largest determining factor of forage quality is the stage of maturity. Fresh growth (such as just after
the spring/summer break) is much higher in energy and protein than when it is mature (such as in July
and August).
The grazing land ecosystem can be managed through this gateway by: -
ensuring land is maintained in good condition (ie. the desirable plants are not grazed out),
-
establishing high quality plants such as legumes in the pasture,
-
setting appropriate stocking rates (high stocking rates force animals to eat the poor quality
plants and the stemmy parts of the good quality ones)
-
and by supplementing to overcome nutritional deficiencies when it’s economical to do so.
3
Grass / tree interactions
Why is the tree grass relationship important in the grazing industry?
All of the grazing land in the Burnett is or was woodland, the majority being eucalypt woodland.
Woodland is a term used in grazing land ecology to describe vegetation having a mix of two distinct plant
types: woody species (trees and shrubs) and herbaceous species (grasses and forbs). Where the woody
species comprises commercial timber, these would usually be described as forest.
Most grazing properties in the Burnett derive the majority of their economic value from the herbaceous
layer. Many properties with a mix of land types, some of which are quite productive in terms of timber
production, derive significant income from the woody layer.
Despite the supplementary income derived from trees, most grazing enterprises have traditionally focused
on enhancing the herbaceous layer through clearing and thinning. In the eucalypt forests, this has
occurred on a cyclical basis through-out the last century.
Impacts of trees on grass
Trees can have both a positive and negative effect on the grassy layer, caused by: -
rainfall interception
-
shading
-
root competition (for nutrients and moisture)
-
microenvironment changes
-
effects on soil condition (soil structure)
-
nutrient cycling
Diagram 2. Impacts of trees on pasture
Trees intercept rainfall and store part of it in the canopy from where it evaporates. Some species can
‘funnel’ rainfall from the canopy, down the trunk onto the ground directly beneath the tree. The tree
canopy can also alter the rain droplet size and the velocity at which it falls, which in turn can lessen the
impact of heavy rain on soil surface condition.
4
The tree canopy captures sunlight and prevents it from reaching the grass layer. The proportion
intercepted varies between species, canopy health, season and time of day (especially for the eucalypts
and acacias). In the closed forest types (scrubs, rain forest, wet sclerophyll) grass is generally absent, but
most land types used for grazing have a grassy understorey.
Trees can act as nutrient pumps where they draw nutrients from deeper in the soil profile (from where
grasses can’t access them) and cycle them through leaf fall into the top soil. Tree canopies can also trap
dust which is washed into the soil beneath them with rain. Often the soil biological activity is higher
beneath trees and the subsequent soil structure benefits.
The net result is that pasture quality is often higher under trees compared with pasture growing in the
absence of trees.
Competition
Despite the benefits of trees in terms of pasture quality the net effect of trees is to suppress pasture
growth. This is due primarily to competition for soil moisture. The impact of this competition on pasture
growth is related to tree density. A useful measure of tree density is tree basal area (TBA) which is the
sum total of the cross sectional area of all tree stems measure at 30 cm from the ground. Foresters often
use the term ‘stand basal area’ to describe the same measurement.
Generally pasture growth decreases with an increase in TBA. In drier forests, this tends to be a curvilinear
response; in moister forests the response in more linear.
Impact of TBA on grass production
Ironbark and
spotted gum duplexes and
loams
Spotted gum and
wattles - sandy
duplexes
Annual grass growth (kgDM/ha)
6000
5000
4000
Bluegum flats
3000
2000
1000
0
0
2
4
6
8
10
12
14
16
18
20
TBA (m^2/ha)
Graph 1. Impact of tree density on grass production
In the coastal Burnett, the major land types used for timber production are those with a high proportion of
spotted gum. The best ‘dual purpose’ country is the ironbark and spotted gum on duplexes and loams
(derived from granodiorites). Bluegum flats are usually the most productive in terms of cattle production,
but also have good potential for timber production.
Graph 1 shows the impact of TBA on grass production for these three land types. The impact tends to be
linear on the productive bluegum flats and curvilinear for the generally low producing spotted gum and
wattle country.
Generally, fully clearing heavily timbered country leads to a three to four fold increase in pasture
production. However, in many of the eucalypt forests, initial clearing costs and ongoing regrowth
management renders such clearing as uneconomical. This is especially the case when the eucalypt forest
has potential to produce millable hardwood and fencing timber.
5
Note Broadscale clearing of vegetation mapped as remnant under the Vegetation Management Act, is
now illegal in the absence of appropriate approval.
Other benefits of trees
Forests provide vital habitat for faunal biodiversity and are an important source of floristic biodiversity.
In the coastal Burnett, as in the rest of the south east Queensland bioregion, the vast majority of remnant
vegetation is eucalypt forest (much of which is on freehold land).
Trees also play an important role in the hydrological cycle within a landscape (diagram 3). Retaining deep
rooted perennial plants, such as trees, reduces the risk of dryland salinity. Hazardous land types, such as
those with saline sub-soils (such as those derived from marine sediments), or land types down slope of
highly permeable soil types (such as deep red soils), can be protected by retaining trees in the recharge
areas.
Diagram 3. Role of forests in preventing dryland salinity
Impact of thinning for forest production and the grazing enterprise
Optimal tree stocking densities
As mentioned already in the workshop, trees need space to grow. Cyclical harvesting and thinning of a
stand is critical in optimising the productive potential of that stand. The optimal stocking densities for a
range of tree size classes are given in table 1. However, in a native eucalypt forest all size classes are
generally present. Depending on the relative fertility of the site and climate constraints, optimal timber
production for a mixed stand with all tree diameter classes present, usually occurs when the tree stocking
density is around 150 stems per ha with a total tree basal area of 12 to 15 m2/ha (table 2).
6
Table 1. Optimal tree stocking densities for individual tree size classes.
Tree diameter range
(cm)
Spacing (m)
Stocking density
(trees/ha)
Tree basal area
(m2/ha)
10 - 20
5–7
200
3.5
20 - 30
7 – 10
100
5.0
30 - 40
10 – 12
70
7.0
>40
12 - 15
45
9.0
Table 2. Impact of tree stocking density on tree basal area for an optimally stocked forest and an
overstocked forest; both with a mix of tree size classes.
Forest with optimal stocking
Tree diameter
range (cm)
Overstocked forest
Stocking density
(trees/ha)
Tree basal area
(m2/ha)
Stocking density
(trees/ha)
Tree basal area
(m2/ha)
10 - 20
40
0.8
100
2.0
20 - 30
40
2.1
75
4.0
30 - 40
35
3.6
60
6.1
>40
35
5.8
45
9.2
150
12.3
280
21.3
For the main timber producing land types in the coastal Burnett (ie. those with spotted gum forest), a well
managed stand with optimal stocking density, should yield about 1 m3/ha/year. In this situation,
individual trees in the smaller diameter classes would grow at a rate of about 1cm DBH/year. The gross
value would be between $80 and $100 /ha/year.
Post thinning pasture production
Following a harvest or thinning operation, the stand TBA will be reduced. This will lead to long term
productivity gains in the forest, but will also result in a short term increase in grass production. Table 3
shows the impact of tree density (as measured by tree basal area) on grass production.
Thinning an overstocked stand to optimal stocking density may reduce the tree basal area from 24 m2/ha
to 15 m2/ha. This would lead to an increase in pasture production of between 40% and 50%. A heavy thin
and harvest that reduces TBA to 10 m2/ha could lead to and increase of pasture production of between
85% and 120%, the proportional increase being greater on the more fertile land types (such as the
bluegum flats).
A significant regeneration of the forest usually follows a disturbance, and if left unmanaged can lead to a
rapid increase in TBA. In these situations the increase in grass production following a harvest or thinning
would be short lived.
7
Table 3. Impact of Tree basal area on grass production for three coastal Burnett land types.
Average annual grass production
(kg DM /ha)
TBA (m2/ha)
Ironbark and spotted
gum - duplexes and
loams
Spotted gum and
wattles - sandy
duplexes
Bluegum flats
0
4300
3300
5500
1
4100
3000
5300
2
3800
2700
5000
4
3200
2300
4500
6
2600
1900
4000
8
2200
1700
3600
10
1900
1500
3200
12
1600
1300
2800
15
1400
1200
2300
20
1100
900
1700
24
1000
800
1500
Changes in carrying capacity
An increase in pasture production leads directly to an increase in carrying capacity. The carrying capacity
of a land type is based on a safe utilisation rate of between 30% and 35% of the average annual pasture
growth, depending on the relative fertility of that land type. This means that a long term stocking rate will
be set at a level such that only the desired proportion of annual grass growth is grazed. Generally stocking
rates are based on an adult equivalent (AE = 450 kg dry beast) and expressed in hectares per adult
equivalent (ha/AE). Table 4 and graph 2 show the impact tree density has on carrying capacity.
Table 4. Impact of Tree basal area on carrying capacity for three coastal Burnett land types.
Land type
IB&SG_dup,loam
IB&SG_dup,loam
IB&SG_dup,loam
IB&SG_dup,loam
IB&SG_dup,loam
SG&W-duplexes
SG&W-duplexes
SG&W-duplexes
SG&W-duplexes
SG&W-duplexes
Bluegum
Bluegum
Bluegum
Bluegum
Bluegum
* where :
flats
flats
flats
flats
flats
Tree basal
Pasture
area
Utilisation growth (kg
(m²/ha)
(%)
DM/ha)
TBA
U
PG
24
30
1000
15
30
1400
30
10
1900
30
6
2600
30
0
4300
Pasture
utilised
PG*U
300
420
570
780
1290
Forage
demand (kg
DM/AE/year)
FD
3,650
3,650
3,650
3,650
3,650
Carrying
capacity
(ha/AE)
FD/*(PG*U)
12.2
8.7
6.4
4.7
2.8
24
15
10
6
0
30
30
30
30
30
800
1200
1500
1900
3300
240
360
450
570
990
3,650
3,650
3,650
3,650
3,650
15.2
10.1
8.1
6.4
3.7
24
15
10
6
0
35
35
35
35
35
1500
2300
3200
4000
5500
525
805
1120
1400
1925
3,650
3,650
3,650
3,650
3,650
7.0
4.5
3.3
2.6
1.9
- IB&SG_dup,loam
- SG&W-duplexes
= ironbarks and spotted gum on duplexes and loams
= spotted gum and wattles on duplex soils
8
Reducing tree basal area as part of a harvest and/or thinning operation will lead to a short term increase in
grass production. Although this increase in grass production may lift carrying capacities significantly, the
effect will be short lived.
Impact of TBA on Carrying cappacity
CC (ha/AE)
16.0
14.0
IB&SG_dup
,loam
12.0
SG&Wduplexes
10.0
Bluegum
flats
8.0
6.0
4.0
2.0
0.0
0
5
10
15
20
25
TBA (m^2/ha)
Graph 2. Impact of TBA on carrying capacity
Generally, the retained trees in the stand grow relatively quickly which leads to an increase in tree basal
area. Further more, there is usually a significant regeneration event following disturbance in a forest (this
is one of the aims of sustainable silvicultural practice). This regeneration event also increases tree basal
area.
Where a forest is retained primarily for silvicultural purposes, the aim is to convert nutrients, water and
sunlight into wood, not beef.
9
Roles for fire
Grazing
Fire is an important management tool for graziers especially in the grazed woodlands. Graziers can
responsibly use fire to: -
remove moribund growth (improve feed quality)
-
even out patch grazing
-
alter species composition (increase the proportion of desirable pasture species)
-
reduce wildfire risks
-
assist with low key establishment of legumes
-
manage the tree – grass balance
In the coastal Burnett most native pastures are burnt on a regular basis. The frequency will vary with
seasonal conditions but averages out at 2 to 3 years. Most graziers will burn at the end of the winter
following 30 mm to 50 mm of rainfall (usually any time from the end of August). Compared with unburnt
pastures, burnt pastures tend to be higher in protein and have more accessible green leaf during the
growing season. Animal production is subsequently enhanced during this period.
Where the aim is to improve species composition (eg. remove wiregrass), fire should be used annually.
Pastures should be spelled following the fire to enable the desirable species to establish and /or replenish
stored root reserves.
Patch grazing is a desirable behaviour for grazing animals as it allows them to optimise nutrient intake;
restricting it will reduce individual animal performance. However, persistent patch grazing over several
years will reduce land condition in the grazed patches. Fire is a useful tool for evening out the patch
grazing from one year to the next. The patches that are relatively ungrazed in one year will tend to burn
well at the end of that dry season and become the grazed patches in the following growing season and
vice versa.
Graph 3. Impact of tree height on susceptibility to fire
10
Fire is a useful tool in reducing eucalypt seedlings and a shrubby understorey. Many acacias are
susceptible to frequent ‘cool’ fires. In some woodlands, a fire frequency of 3 years or less has been shown
to break the life cycle of wattles. Eucalypt seedlings less than 1 m high are susceptible to fire. Larger
saplings, though not killed by fire, can be damaged enough to reduce their competitive advantage over
grass.
An effective fire to reduce tree and shrub competition may require fuel loads of greater than 2000 kg/ha.
If the aim of the fire is to even out patch grazing or change species composition, fuels loads as low as
1000 kg/ha may be effective. Grazing management needs to be consistent with the planned fire regime to
ensure sufficient fuel and post fire pasture growth.
Native forest management
Where woodlands are retained primarily for timber production, fire is still a useful tool but the fire
regimes and management programs will differ slightly to those used primarily for grazing. Fire is an
important tool for seed germination following a harvest, and for managing a shrubby understorey. A post
harvest fire also removes residue (such as tree heads, log dumps etc.) left over from the harvest operation
itself.
The frequency of fire in the dry forests (of which spotted gum forest is one type), is a little longer than
that for grazing and averages out at 2 to 5 years.
The intensity of the fire and its timing in relation to seasonal conditions is also a little different to that
used for grazing. Hot fires can damage growing stock, scorch crowns and lead to defect in the log butt.
The fire regime used in native dry forests is for a ‘cooler’ burn during May or June.
Integrating forest management and Grazing
Enterprise focus
In the coastal Burnett several land types have the ability to grow either cattle or timber (and in some cases
both). Very little native forests are found on the more productive and developed land types such as blue
gum flats, blue gum and bloodwood on basalt ridges, softwood scrub and hoop pine scrub. These land
types either had little commercial timber initially or the commercial timber was harvested early during
settlement and the land types subsequently cleared for grazing, dairying or cane production. With the
exception of plantation timber, these land types will probably remain dedicated to grazing or agricultural
production.
Much of the remnant native hardwood forest grows on those land types which are generally unproductive
in terms of cattle production (eg. ironbarks, stringybarks and supple jack ridges, mixed eucalypt on
uplifted coastal plains, spotted gum and wattle ridges and gum topped box) and hence have been largely
undeveloped for grazing. While timber production has provided an important income from these land
types, there is room for improved hardwood productivity through a more proactive focus on forest
management. Grazing should be regarded as a secondary enterprise.
There are some land types that are quite productive in terms of cattle production and timber production
(eg. ironbark and spotted gum on duplexes and loams and ironbarks, bloodwoods on non-cracking clays,
and blue gum slopes). This has been well recognised by some landholders who manage productive native
forests in conjunction with their grazing enterprise. The challenge for managing these land types is to
strike a balance between cattle production and timber production. The TBA of retained forest may be suboptimal for either grazing or timber production, but may provide the best economic return.
11
Table 5. Grazing gross margins for three land types in the coastal Burnett at different TBA
IB&SG_dup,l
oam
SG&Wduplexes
Bluegum
flats
TBA
24
10
7
0
TBA
24
10
7
0
TBA
24
10
7
0
* LWt gain valued at
C.C.
(ha/hd)
12.2
6.4
5.2
2.8
annual
LWt gain
(kg/hd/yr)
140
140
140
140
Annual LWt Cattle Gross
gain
Value *
(kg/ha/yr
($/ha/yr)
11.5
17.26
21.9
32.79
27.0
40.56
49.5
74.22
Variable
costs
($/ha/yr)
3.31
6.29
7.78
14.24
Gross
Margin
($/ha/yr)
13.95
26.50
32.78
59.98
C.C.
(ha/hd)
15.2
8.1
6.8
3.7
annual
LWt gain
(kg/hd/yr)
95
95
95
95
Annual LWt Cattle Gross
gain
Value *
(kg/ha/yr
($/ha/yr)
6.2
9.37
11.7
17.57
14.1
21.08
25.8
38.65
Variable
costs
($/ha/yr)
2.52
4.72
5.66
10.38
Gross
Margin
($/ha/yr)
6.85
12.85
15.42
28.27
C.C.
(ha/hd)
7.0
3.3
2.7
1.9
annual
LWt gain
(kg/hd/yr)
170
170
170
170
Annual LWt Cattle Gross
gain
Value *
(kg/ha/yr
($/ha/yr)
24.5
36.68
52.2
78.25
61.9
92.92
89.7
134.49
Variable
costs
($/ha/yr)
5.99
12.78
15.18
21.97
Gross
Margin
($/ha/yr)
30.69
65.47
77.74
112.52
$1.50
If the timber is valued at $80 to $100 /m3 and a well managed stand will yield 1 m3 /ha/year, it is easy to
see from table 5, that the spotted gum and wattle country will never generate the same income from beef
that it can from timber (even if it was fully cleared). The fact that you do get some cattle production ($6
to $12 /ha/year) is a bonus and contributes to enterprise cash flow.
Conversely, cattle production from productive blue gum flats, even at moderate TBA, will probably outcompete timber production. Considering very few of these blue gum flats contain remnant vegetation, the
focus should be grazing. Where a blue gum flat is mapped as remnant, for legal reasons the focus will be
timber production, but the short term increases in carrying capacity associated with harvesting and
thinning will also be economically important for the grazing enterprise.
Those land types that are reasonably productive for both grazing and timber pose a challenge in
determining enterprise focus. Often landholders will choose to retain trees on these land types at a TBA
that is sub-optimal for either grazing or timber production, but when the enterprises are combined they
yield suitable long term financial returns. As an example, retaining trees on a land type such as ironbark
and spotted gum on duplexes and loams at between 7 to 12 m2 /ha TBA, may only yield about ½ m3
/ha/year in timber production, which equates to $40 to $50 /ha/year. However, when this is added to the
cattle production of $20 to $30/ha/year expected at this TBA, it represents a better long term return than
fully clearing for grazing alone.
Grazing management
Where native forests are grazed (or where grazing land contains stands of productive forest), grazing
management is important in terms of the grazing enterprise, but also in terms of the management of the
native forest.
12
Generally, grazing management is a tool for managing grazing lands and is about when and where cattle
graze. It is influenced by infrastructure such as fencing and watering facilities, incorporates a range of
grazing systems, and is linked to other grazing management tools such as fire, sown pastures, weed
management and woodland management.
The fundamental components of sustainable grazing management include: -
matching feed demand to feed supply (utilisation rates and forage budgeting)
-
ensuring residual ground cover at the end of the dry season (always come out of a drought
with stubble on the ground)
-
strategic spelling during critical grass growth phases (wet season spelling)
The main link between grazing management and timber production is through managing fuel to achieve
effective fire regimes. Grazing too heavy reduces fuel loads beyond which a fire will carry (especially
during the cooler months of the year); not grazing or grazing too leniently may result in high fuel loads
that increase wildfire risk and the potential to damage standing timber.
The other link between grazing management and timber production is about reducing the damage that
cattle can do to regeneration. Cattle will browse, especially during the autumn and winter months when
pasture protein levels are low. At these times they can considerably damage eucalypt seedlings and small
saplings. Post harvest regeneration is a critical time in the silvicultural cycle. Restricting cattle access to
native forest stands at this time may help the regeneration process.
Opportunities for low key pasture development
Most land types that support productive native forest are not suitable for intensive development including
sown pasture establishment. They are however suitable for ‘low key’ development based on establishing
perennial tropical legumes into native pasture. The establishment of legumes such as the stylos (fine stem
stylo and shrubby stylo) and Wynn cassia into native pastures has been demonstrated to lift individual
animal liveweight gains by 20 to 50 kg/hd/year.
The soil disturbance associated with the harvest operation of a native forest is an ideal opportunity to
broadcast legume seed. Establishment will generally be slow, but within several years, the legume should
establish to the point that it will contribute to animal liveweight gain.
The temptation to lift stocking rates following legume establishment should be avoided. Cases of legume
dominance and the associated sustainability risks (such as soil erosion) can generally be attributed to
increased stocking rates post legume establishment and lack of strategic spelling. Native pastures that
become dominated by legumes generally fail to develop sufficient fuel loads for effective burns.
Conclusions
The land you manage is a complex and diverse ecosystem. Keeping land in good condition ensures the
ecosystem functions efficiently. “Tools” such as infrastructure, grazing systems, fire, sown pastures, weed
control and timber treatment are used to maintain or improve land condition.
In the coastal Burnett several land types continue to provide landholders with income from both grazing
and forestry. Productive grazing land types generally provide little opportunity for income from native
hardwood forestry; due mainly to the economic advantage of grazing over timber and the fact that little
remnant forest exists on these land types.
The focus of management of those land types that are generally unproductive from a grazing perspective
and that still contain significant forest cover should shift from grazing to native forest management.
The truly dual purpose land types have the potential to be managed at tree basal areas that are sub-optimal
from either the grazing or timber production perspective, but when the productivity from the combined
enterprises is taken into account, produces an optimum economic outcome.
13