Performance Audit Report - Forestry Corporation · Yield Forecasts ‐ Eden Regional Forest...

Yield Forecasts ‐ Eden Regional Forest Agreement of 10 20/3/12

Performance Audit Report

Yield Forecasts – Eden Regional Forest

Agreement

Issue The Auditor General’s Performance Audit “Sustaining Native Forest Operations: Forests NSW” of April

2009 included an action item (Recommendation 3), requiring Forests NSW to “Undertake and publicly

report the results of a review of yield estimates for native forests in Southern Region including Eden,

South Coast & Tumut”

This report addresses the review of yield estimates for Eden Regional Forest Agreement (RFA), in the

form of a review of timber supply from the Eden sub‐region of the Forests NSW Southern Region.

Background In 2008 Forests NSW commenced an internal review of 1998 wood supply modelling for Eden RFA area.

This review was extended in 2011‐12 and forms the basis of this report.

Aspects of the 2008 study included:

Logging history and stand structure updated to end 2007.

No additional inventory was included.

Regrowth was modelled using the REDEN model, which was a local growth and yield simulator

incorporating 9,000+ inventory plots, unique local biometrics (growth models, stem volume

equations, species and site specific height functions) and thinning schedules.

Yields for multi‐age forest were based on standing volume only (no growth).

Net harvest area was recalculated but no modifiers were applied.

Yield scheduling undertaken using Remsoft® Woodstock planning system.

Species modelling based on forest typing.

Future sawlog/pulp volume proportions from current regrowth incorporate scaling factors.

It should be noted that that REDEN is not consistent with FRAMES (the Forests NSW Forest Resource

And Management Evaluation System). The location specific biometrics and underlying inventory

program are no longer supported.

Timber harvesting in the Eden management area is in transition with harvesting changing from

remaining multi‐age forest (harvested with alternate coupe silviculture) to older fire regrowth (which is

90% thinned) to younger harvesting regrowth.


Timber supply from the Eden area is covered by a number of agreements

Agreement Length Dates

(yr)

Eden Regional Forest Agreement 20 August 1999 – 2019

Eden Forest Agreement 20 5/3/1999 – 5/3/2019

Eden Integrated Forestry Operations Approval (IFOA) 19 1/1/2000 – 31/12/2018

Wood Supply Agreement (WSA) with Blue Ridge Hardwoods ~ 20 7 /3/1999 – 1/1/2019

Project Design The modelling undertaken as part of this review provides more detail on future sawlog and pulpwood

volumes for the remainder of the Wood Supply Agreement (WSA) which extends to the end of 2018.

Changes included in the 2011‐12 review were restricted to:

Updating area statements, incorporating:

o Reanalysis of the remaining mature age forest (MAF) resource including identifying

areas not harvested in previous operations. Approximately 20% of this area was field

verified; the remainder was updated using aerial photography interpretation (API) and

GIS analysis.

o Areas of older fire regrowth and harvesting regrowth forest were updated to

incorporate harvesting to 30 June 2011.

o Allowing for operational factors, such as excluding small areas theoretically available for

harvesting where these are below a threshold size.

Incorporating Net Harvest Area Modifiers (NHAM) calculated as part of the 2011 NHAM review

(reported separately). The NHAM factors were applied to the updated area statements.

Reviewing the thinning strategy including extension of the “thinning window” – the age range

where thinning is permitted in the model and providing more flexibility with the way thinning is

scheduled by the model.

Revising and simplifying yield tables by:

o Removing scaling factors used in the previous model.

o Scaling raw yield data to match previous yield table volumes, but in a simpler format.

o Cross‐checking scaled yields with recent harvest volumes to confirm that the yield tables

were providing comparable results.

Updating recovery information for regrowth stands based on actual harvest data – realised

sawlog volume changed to 50% of yield table volume (up from 30%); realised pulp volume

changed to 60% of yield table volume (up from 50%).

Investigating impacts of changes to minimum harvest age.

Investigating the effect of reducing sawlog small end diameter (sed) from 30 cm to 25 cm.


Current resource

The area base for this forecast covers the Eden RFA Region which is included in the Eden sub‐region of

Forests NSW Southern Region (see Figure 1). The forest resource can be categorised into areas of high,

medium and low site quality and by growth stage. Figure 2 shows the extent of these site quality areas

across the Eden RFA region. Figure 3 shows the location of multi‐age forest, pre‐1970 regrowth and

post‐1970 regrowth stands.

Figure 1: Extent of study area for Eden region yield estimates.

Berridale

Cobargo

Bermagui

Nimmitabel

Bemboka

Eden RFA Region

Bega Tathra

Candelo

Bombala Merimbula

Pambula

Delegate

Eden

Eden RFA RegionState Forests 2011

Planted Forests

Native Forests


Figure 2: Eden RFA Region Site Quality.

Berridale

Cobargo

Bermagui

Nimmitabel

Bemboka

Eden RFA Region

Bega Tathra

Candelo

Bombala Merimbula

Pambula

Delegate

Eden

Eden RFA RegionSite Quality

Site Quality

High

Medium

Low


Figure 3: Eden RFA Region Forest Structure.

Berridale

Cobargo

Bermagui

Nimmitabel

Bemboka

Eden RFA Region

Bega Tathra

Candelo

Bombala Merimbula

Pambula

Delegate

Eden

Eden RFA RegionForest Structure

Forest Structure

Pre 1970 Regrowth

Post 1970 Regrowth

Multi-age Forest


The Eden management area has a gross area of just over 164,200 ha. The net area used in the 2008

modelling was 95,945 ha. The revised net harvestable area (NHA), incorporating Net Harvest Area

Modifier (NHAM) factors and additional area statement adjustments discussed above, is 88,018 ha. This

is a reduction of 7,927 ha (8%) from the 2008 area.

Table 1 below summarises the NHA by age class and thinning category.

Table 1: Net harvestable area by age class and thinning category

Resource Category Unthinned Thinned Total NHA NHA (ha) NHA (ha)

(ha)

Multi‐age forest (MAF) 13,616 13,616

Pre‐1970 Fire Regrowth 748 1,826 2,574

Post‐1970 Regrowth 63,706 8,122 71,828

Total 78,070 9,948 88,018

Estimates of standing volume associated with multi‐age forest (MAF) in the 2008 model were generally

sourced from older field estimates. The process to update MAF area for this model also included yield

verification of standing volume using field inventory or links to harvested yields from adjacent areas.

Approximately 1,100 ha of the 13,616 ha of MAF did not have any form of yield verification. Estimates of

standing volume for this area were made using the more conservative 2008 yield tables.

Table 2 below summarises the standing volume by site quality remaining on multi‐age forest. Note that

there is no growth associated with this forest type.

Table 2: Standing volume in multi‐age forest (MAF), Eden management area

Site NHA HQ vol Tot HQ vol Quality (ha) (m3/ha) (m3)

High 3,822 18.1 69,200

Medium 4,874 8.4 40,900

Low 4,921 4.8 23,600

Total 13,616 9.8 133,700

Scenarios

Two wood supply scenarios were modelled using Woodstock and updated net harvestable area.

Non‐Declining Sawlog Yield scenario – The objective of this scenario was to balance the supply

of high quality sawlog (Large Graded Log and Small Graded Log) to ensure future yields are

always the same or higher than for the previous period. The model was run over a 100 year

planning horizon.


Wood Supply Agreement (WSA) scenario – The objective of this scenario was to meet current

(1999‐2018) WSA volumes, while continuing to maximise long term sustainable supply levels of

high quality sawlog.

Results

Non‐Declining Sawlog Yield scenario

Table 3 and Figure 4 summarise the results of the even flow scenario, showing volume (m3/year) of high

quality sawlog and pulp available summarised by 4 year periods (commencing 2011) over a 48 year

planning horizon. Four year periods have been used to align the model outputs with the end of the

Wood Supply Agreement.

Table 3: Available volume (m3/year) over 48 year horizon for all products.

Product Class 4 year period

1 2 3 4 5 6 7 8 9 10 11 12

HQ Large Sawlog 16,100 16,000 12,800 7,300 5,900 14,000 21,200 35,400 34,500 34,500 36,300 36,700

HQ Small Sawlog 0 200 3,400 8,900 10,200 13,000 21,900 37,900 38,800 38,800 37,000 36,600

Total HQ Sawlog 16,100 16,100 16,100 16,100 16,100 27,000 43,100 73,300 73,300 73,300 73,300 73,300

Pulp 285,600 285,600 285,600 285,600 285,600 242,800 228,500 228,500 228,500 228,500 228,500 228,500

Figure 4: Non‐Declining Sawlog Yield scenario ‐ available volume (m3/year) over 48 year horizon for

high and low quality product grades.

80,000

70,000

60,000

(m3/yr)

50,000

Volume 40,000

30,000

20,000

10,000

01 2 3 4 5 6

4YearPeri

7 8

ods

9 10 11 12

HQLargeSawlog HQSmallSawlog TotalHQSawlog


Wood Supply Agreement scenario

Table 4 and Figure 5 summarise the results of the scenario to meet existing wood supply agreement

commitments. Results are given for high quality sawlog and pulp per year for each 4 year period.

Periods 1 and 2 cover the remaining WSA years 2011 to 2018.

Table 4: Available volume (m3/year) over 48 year period for high quality products – WSA scenario.

Product Class 4 year period

1 2 3 4 5 6 7 8 9 10 11 12

HQ Large Sawlog 23,000 19,800 10,800 8,800 6,900 8,000 8,900 31,700 34,300 35,300 35,000 33,500

HQ Small Sawlog 0 3,200 7,800 10,200 12,300 11,200 10,300 36,400 37,100 36,200 36,500 38,000

Total HQ Sawlog 23,000 23,000 18,600 19,000 19,200 19,200 19,200 68,100 71,500 71,500 71,500 71,500

Pulp 279,800 279,800 279,800 279,800 279,800 237,800 223,800 223,800 223,800 223,800 223,800 223,800

Figure 5: Wood supply agreement scenario ‐ available volume (m3/year) over 48 year horizon for

high and low quality product grades.

80,000

70,000

60,000

(m3/yr)

50,000

Volume 40,000

30,000

20,000

10,000

01 2 3 4 5 6

4YearPeri

7 8 9

ods

10 11 12

HQLargeSawlog HQSmallSawlog TotalHQSawlog


Comparison

Table 5 compares the results of the two scenarios. These results show a significant decline in the volume

of high quality sawlog follow the end of the Wood Supply Agreement, relative to the non‐declining

sawlog yield scenario.

Table 5: Comparison of high quality sawlog volume (m3/year) available from Non‐declining Sawlog

Yield and Wood Supply Agreement scenarios.

Period Even Flow scenario Wood Supply Agreement scenario

Difference

1 16,100 23,000 6,900

2 16,100 23,000 6,900

3 16,100 18,600 2,500

4 16,100 19,000 2,900

5 16,100 19,200 3,100

6 27,000 19,200 ‐7,800

7 43,100 19,200 ‐23,900

8 73,300 68,100 ‐5,200

9 73,300 71,500 ‐1,800

10 73,300 71,500 ‐1,800

11 73,300 71,500 ‐1,800

12 73,300 71,500 ‐1,800


Conclusion This review demonstrates that Wood Supply Agreement (WSA) volumes can be met for the duration of

the WSA timeframe. High quality (large graded and small graded) sawlog will predominantly be sourced

from multi‐age forest and older fire regrowth.

Following the end of the Wood Supply Agreement in 2018, the model shows the rapid transition to log

supply from the regrowth resource. A drop in the sawlog supply during this transition is mitigated by

minor adjustments to the silvicultural strategy for approximately 10 years. During this period the

minimum harvest age for regrowth stands is allowed to drop to 50 years. After this period the minimum

harvest age is reset to 60 years.

A further adjustment was applied to the sawlog yield data to bring it in line with sawlog specifications

applied more generally in NSW coastal forests. The current minimum sawlog small end diameter (sed)

specification of 30 cm was reduced to 25 cm sed. This results in a 10% increase of sawlog volume. The

minimum sawlog diameter adjustment is applied to the regrowth resource only.

There will be several challenges associated with supplying the modelled volume including: managing the

local reduction in high quality log volume post‐WSA in the context of broader regional log supply;

managing the transition from multi‐age forest to older fire regrowth and younger harvesting regrowth;

addressing the incomplete inventory of fire regrowth and harvesting regrowth stands; and managing

changes in the supply of pulp from multi‐age forest to thinning of harvesting regrowth stands.

A number of issues identified by this review will require further work to support the transition from

multi‐age forest and older fire regrowth to younger regrowth. These include:

Review of log product definitions, particularly smaller sawlog.

Ongoing verification of recovery and actual log volumes and dimensions harvested (ie are

assumptions about 25 cm sed sawlog being achieved).

Comprehensive forest structure mapping using remote sensing to provide a more accurate

picture of the regrowth resource.

Developing a spatial version of the resource database including:

o Forest structure

o Age Class of regrowth

o Thinning status

o Site Quality.

Incorporating REDEN growth and yield models in the FRAMES Growth and Yield simulator. This

would allow tree level quality and product data to be included in modelling.

Developing new growth models in FRAMES using plot data updated with thinning status and age

class.

Collection of additional data to enable review and refinement of product proportion information

for regrowth thinning and harvesting.

Further refinement of the Net Harvest Area Modifier to reflect harvesting practices in regrowth

forest areas.

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