Calculating the sustainable wood supply
from Tasmania’s public forests
Mike McLarin
Senior Forest Resource Planner
Forestry Tasmania
What I’d like to do is provide you with an insight into “calculating the
sustainable wood supply, often referred to as the sustainable yield, from
Tasmania’s public forests”...
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Outline
• Scope
• Definition and Description
• 2002 5-yearly RFA Wood Review
• 2005 Integrated Forest Strategy (part of the TCFA)
• A Forest Estate Model example
First I’ll scope what I am talking about today.
Then move onto a definition of sustainable yield, and a description of the
silvicultural systems used in the forest to produce the wood, and the modelling of
our forest estate wood supply.
I’ll follow that by looking at output from 2 processes:
The last 5-yearly RFA Wood Review in 2002 (this is a requirement of the
Tasmanian Regional Forest Agreement, between the Federal and Tasmanian
State Governments, signed in 1997, covering all Tasmania’s forest and their
management), and
The more recent Integrated Forest Strategy - announced as part of the Tasmanian
Community Forest Agreement in May last year (again this agreement is between
the Federal and Tasmanian State Governments, addressing oldgrowth reservation
and alternatives to clearfelling in oldgrowth forests, plus many other issues).
You can find these documents on FT’s website, under Publications.
And finally we’ll look at a real-life forest estate model example.
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Wood productivity in balance with multiple forest values
protect-fauna/flora
wood products
leatherwood honey
water and recreational activities
The concept of sustainable yield forms part of, but should not be confused with,
the overarching goal of sustainable forest management.
Sustainable forest management is concerned with whether forests are being
sustainably managed for their full range of benefits - environmental, economic
and social - for current and future generations, providing a balanced return from
all forest uses.
Our goal is “wood productivity in balance with multiple forest values”.
Today I’m addressing directly the wood products component only of these
multiple forest values.
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Tasmania
6.8 million hectares
40% private land
22% State forest
38% other public land
Now to the landbase...
Of the 6.8Mha of Tasmania 40% is privately owned
(yellow colour through the Midlands predominantly)
Of the 60% of public land about a third is State forest, managed by FT
(the green bit = 1.5Mha)
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Land Use Classification of State Forest
State forest = 1.5 million hectares
17%
49%
34%
Provisional Coupes
Formal & Informal Reserves
Outside Provisional Coupes
Provisional coupes (often called provcoupes for short) are areas specifically
identified for wood production (about a half of State forest).
It is important to remember that these areas are identified initially at a strategic
level, and represent gross areas. What actually gets harvested after operational
planning is often much less, to protect non-wood values within the provisional
coupes.
About a third of State forest is reserved, to protect multiple forest values, and are
not used to produce wood.
The remaining 6th of State forest has not been identified specifically for either
wood production or reservation.
Today I’m focussed on the provisional coupe area for wood production only.
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Management of Provisional Coupes
Provisional Coupes = 732,000 hectares
7%
6%
6%
81%
Eucalypt Native Forest
Eucalypt Plantations
Softwood Plantations
Special Species Timbers
And finally, within the provisional coupes, today I’m talking about the Eucalypt
Native Forest and Eucalypt Plantations only - almost 90% of all provisional
coupe area.
Special Species Timbers wood supply is covered in next month’s lunchtime talk.
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Scope
• Strategic
• Wood
• Provisional Coupes
• Eucalypts
So the scope for today’s talk is wood production from eucalypt provisional
coupes, and has a strategic, big-picture, long term view.
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Definition
The sustainable yield of a forest is the maximum level
of commercial timber (or product mix) that can be
maintained under a given management regime
For wood products, “the sustainable yield…”
Key concepts are:
Maintaining a level of harvest,
of a timber product, or products, given a certain forest management approach.
For any forest area, there is no single measure of sustainable yield.
The sustainable yield of timber products are determined not only by the nature of
the resource, but also by the objectives and constraints that make up a
management strategy.
For example, a forest managed on short rotation ages to produce pulpwood, will
have a different sustained yield, compared to the same forest managed on longer
rotation ages to produce sawlogs.
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Forestry Act 1920
Section 22AA requires Forestry Tasmania to make
available for the veneer and sawmilling industries,
each year, a minimum of 300,000 cubic metres of
eucalypt high quality sawlogs
The Forestry Act provides clear guidance for sustained yield from Tasmania’s
State forests.
“Section 22AA requires…”
So what do we do in the forest to produce the wood?
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Silvicultural Systems
• Partial harvesting systems used in
most dry forests
• seed tree, shelterwood, advanced
growth retention, sawlog retention etc
• one or more harvests during 90 year
period
There are a range of silvicultural systems used in the forest to produce wood.
“Partial harvesting systems…”
Partial harvesting in dry forests accounts for about half of the area harvested each
year.
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Silvicultural Systems
• Clearfell, burn and sow (CBS) is
currently the most effective and
practicable system in wet forests
•
notional rotation 90 years
• Thinning of suitable regeneration
areas to accelerate sawlog growth
• notional rotation 65 years
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Silvicultural Systems
• Aggregated Retention
• notional rotation 90 years
• retaining 20% aggregates
A new approach - an alternative to clearfelling in oldgrowth forests - looking to
retain 20% of the initial forest within the harvest area.
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Silvicultural Systems
• Plantation established with both
low and high prune regimes
• rotation 20-25 years
Relatively small areas, but an important source of future wood supply,
given increased levels of native forest reservation.
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Aerial photograph of forest landscape
Thinned native forest
Native forest
Plantation
As a result of these silvicultural systems, across the landscape we have areas of
couped native forest and plantations, some thinned, growing to produce future
wood supply by being harvested at different times...
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Forest Estate Model Output
Harvest Year
…and this is represented in forest estate models, like this one.
This model output shows a harvest scenario for provcoupes over a ten-year
period - colours representing a harvest year (provcoupes are the polygons on the
map).
It is important to remember that, in a strategic wood supply model like this,
identification of an area does not necessarily mean that area exactly will be
harvested at that time - rather it is an indication that forest of that type and in that
location is suggested for harvest then.
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Key Elements of Forestry Tasmania’s Planning System
Photo-interpreted
Forest Types
Management
Decision
Classification
Provcoupes
Now to the “Key Elements of FT’s Planning System”...
The forest is a multi-layered mosaic of many elements:
1. The thin lines define polygons representing different forest types. A program
of aerial photography, followed by interpretation of those photographs by FT
staff, creates these polygons in our Geographic Information System (GIS). These
polygons form the basis of strata that are sampled by establishing plots in the
forest, and measuring the trees - numbers, species, size. These measurements are
then fed into growth models to grow the tree measurements for the forest into the
future.
2. Management Decision Classification delineates forest managed for wood
production from forest managed to protect other uses (on this map the green
shades vs. brown).
3. The bright green represents provisional coupes - these are our planning units
for wood production. By intersecting the provcoupes and forest types (with their
grown-on tree measurements) we can calculate current and future log product
volumes on every provcoupe.
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Forest Estate Model Components
• Area of forest (ha)
• Yield of log products (m3/ha)
• Forest management strategy
Simply put, these are the basic components of any forest estate model.
Areas are defined using GIS, like the last slide.
Attached to these areas are yields. A yield in this context is a table of wood
production estimates in m3/ha, for various log products at various ages, derived
from our sample of plot tree measurements.
Finally, the forest management strategy is input, usually as a set of policies, goals
and silvicultural regimes.
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Forest Estate Modelling
• plot-based tree measurement system
• provcoupe-based modelling and projection system
• incorporates environmental constraints
• eucalypt native forest and plantations
• linear programming optimisation
• 90-year timeframe
• 5-yearly reviews (linked to RFA)
• independent external review
Forest estate modelling involves a plot-based tree measurement system, and a
provcoupe-based modelling and projection system (as discussed in the Key
Elements of FT’s Planning System).
Forest estate modelling incorporates environmental constraints, like streamside
reserves, steep land, wildlife habitat clumps and retained aggregates within the
harvest area.
It involves eucalypt native forest and plantations.
Linear programming optimisation is a mathematical method, used in this case to
suggest provcoupes for harvest, given certain objectives and constraints.
It has a 90-year timeframe.
There are 5-yearly reviews of our forest estate modelling, linked to the RFA,
including independent external review, and that’s what we are going to look at
now...
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2002 5-yearly RFA Wood Review
The last RFA Wood Review in 2002 demonstrated a 300,000m3/yr sustainable
yield of eucalypt high quality sawlogs, meeting the Forestry Act requirement. In
the short term harvest is at 350,000m3/yr to meet wood supply contracts to local
sawmillers.
Components of this wood supply over 90 years include native forest partial
harvesting, clearfelling of mature and regrowth trees, followed by regenerated
native forest, and plantations from about 2020 onwards.
Remember that although the future wood supply is from younger forest than
currently harvested, older forest still exists outside provcoupes used for wood
production - that is, the other half of State forest, and the other public forest land
that is reserved.
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2002 5-yearly RFA Wood Review
Figure 7: 2002 Review of Pulpwood Arising Yield from State Forest
4,000,000
3,500,000
Volume cut (m3)
3,000,000
2,500,000
2,000,000
1,500,000
1,000,000
500,000
0
2001 2006 2011 2016 2021 2026 2031 2036 2041 2046 2051 2056 2061 2066 2071 2076 2081 2086
Year starting 1 July
Plantation Sawlog & Solid Wood Processing Residue
Plantation Solid Wood (from Figure 6)
Plantation pulpwood
Native Forest: Regrowth & Regeneration
Native Forest: Partial Harvesting
Native Forest: Mature
Source: Sustainable High Quality Eucalypt Sawlog Supply from Tasmanian State Forest - Review No. 2,
May 2002. Planning Branch, Forestry Tasmania
Associated with the high quality sawlog supply are pulpwood and solidwood
arisings, at about 2.5-3Mm3/yr. These are the other log products, including low
quality sawlogs and peeler logs, that are produced from the forest with the
sustainable yield of eucalypt high quality sawlogs.
The grey colour represents plantation logs suitable for engineered wood products.
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2002 RFA Wood Review
2005 Integrated Forest Strategy
Eucalypt High Quality Sawlog
400,000
400,000
350,000
350,000
300,000
75 000 m3
250,000
Volume cut (m3)
Volume cut (m3)
300,000
200,000
150,000
115 000 m3
200,000
150,000
100,000
100,000
100 000 m
50,000
0
2003
250,000
2008
2013
3
2018
104 000 m3
50,000
2023
2028
2033
0
2003
2008
2013
2018
2023
2028
2033
More recent modelling, to support increased oldgrowth forest reserves and
alternatives to clearfelling in oldgrowth forests, presents a slightly different
picture (on the right). This is the Integrated Forest Strategy - part of the
Tasmanian Community Forest Agreement.
In comparison with the 2002 RFA Wood Review (on the left), variable retention
harvest has been added, and more plantation is required to ensure a sustainable
yield of 300,000 m3/yr, because of increased reservation and alternative
silviculture.
Again, there is a change from harvesting older forests to younger forests in the
future, but there is also 1Mha of oldgrowth forest reserved now under the
Tasmanian Community Forest Agreement.
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2005 Integrated Forest Strategy
Pulpwood and Solidwood Arisings
And for completeness, the pulpwood and solidwood arisings associated with the
eucalypt high quality sawlog supply reduce from about 3Mm3/yr to 2Mm3/yr, as
less older native forest is harvested.
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What happens next?
• District tactical and operational planning
• Rolling Three Year Wood Production Plans
What happens next? - Basically, the implementation of this sustainable wood
supply in the forest. Calculation of the sustainable wood supply, as shown,
provides a target for Forestry Tasmania’s operations.
District staff consider medium-term tactical issues for implementation. This
includes selecting and applying silvicultural systems, dispersing harvest across
the landscape, choosing when to enter new forest blocks, and staging harvest in a
logical sequence.
Infrastructure is put in place and harvest occurs as documented in our Three Year
Wood Production Plans, updated annually. This involves planning for multiple
forest values at an operational level, to gain approved Forest Practices Plans from
the independent Forest Practices Authority, before harvesting occurs.
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Integrated landscape
- native forest - plantations - conservation areas -
So what we’ve got is an integrated landscape...
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A Forest Estate Model Example
And finally, a real-live forest estate model example…
Ageclass structure represents age of areas since the model started running, or
since last harvest.
Residual standing volume is the amount of wood growing in the forest.
The top 2 graphs show annual volume and area cut.
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More information
www.forestrytas.com.au
Publications
Review of sustainable high quality eucalypt
sawlog supply
Towards a New Silviculture in Tasmania’s
Public Oldgrowth Forests (April 2005)
Sustainable Forest Management Report 2003
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End of presentation
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