Following a detailed fire intensity mapping process and an independent review, Forestry Corporation of NSW has released updated 100-year wood supply models for hardwood timber yields from NSW State forests. The 2019–20 Wildfires NSW Coastal Hardwood Forests Sustainable Yield Review and the 2019–20 Independent Review Post Fire Resources are available on the Department of Primary Industries website. Links are provided at the bottom of this page.
What is sustainable yield?
State forests are managed to produce timber responsibly and sustainably, so we can harvest the same amount of timber today and 100 years from today.
Timber is the only major building product that completely regrows and hardwood forests comprise a mix of natural forests and timber plantations that are managed to produce a consistent supply of hardwood timber over the long term.
In plantations, large areas are planted with trees the same age and species and the sustainable yield is calculated using data about the size of the area planted, the age of the trees and growth rates.
Native forests maintain a natural structure, with trees of different species and ages naturally germinating and growing side by side, some of which are set aside for habitat, biodiversity and waterway protection and others of which are periodically harvested for renewable timber.
It takes 30 to 40 years to grow a tree that will produce high quality timber and we harvest about one per cent of the areas we manage each year to maintain forest health, habitat and a sustainable supply of timber. These operations take place in line with strict environmental rules that protect wildlife habitat, rainforest, old growth, riparian zones and other important ecological features across the landscape and in each harvest area. During these operations, certain trees are selectively harvested for timber while others are set aside for habitat, seed generation and future timber production and then the harvest area is regenerated.
Different tree species are found in different forests and grow at different rates, so our models reflect:
The proportion of the overall forest and of each harvest area that is set aside under the detailed environmental regulations that protect wildlife habitat, rainforest, old growth, riparian zones and other important ecological features across the landscape and in each harvest area
Measurements from thousands of randomly located plots where the size, quality and species of all trees are recorded
Growth rates from trees in special permanent plots which have been re-measured regularly so we can track their change
Data from operations that records the volume of timber harvested and the areas set aside.
This data generates detailed models that show how much timber of which types and species can be responsibly harvested in each region each year to ensure the amount of timber available in the forest does not decline over the long term. The sustainable yield doesn’t model the number of trees in the forests, it models the quality and quantity of timber that can be produced from State forests that are identified for timber production, in compliance with the strict environmental regulations.
The sustainable yield models inform how much timber of each product type can be allocated under long-term supply contracts, although for many years Forestry Corporation has harvested and sold less than the modelled sustainable yield.
How did the 2019-20 fires impact the sustainable yield from State forests?
Over the years, State forests have been impacted by fires on a regular basis, both through planned hazard reduction burning and through wildfire. Fire is a natural and frequent part of the Australian landscape and many native eucalypt species have adapted to be quite resilient to fire.
The 2019-20 fires impacted a higher proportion of the estate than any previously recorded fires and, in many areas, the intensity of the fire was severe. An environmental assessment was carried out to understand the impact on biodiversity, flora and fauna, and the sustainable yield models were also reviewed to assess the impact of these fires on the long term available timber resource. This was a detailed process that is described in the Sustainable Yield Review Report.
Key to this review was modelling the severity of fire impact across the landscape and the subsequent impact on the timber products. Forestry Corporation used satellite imagery and on the ground data to map the fire intensity across the State forest estate and model the impact across the timber resource.
Because of the different fire impact and range of species in different regions, the impact on long term sustainable yield is highly variable. The impact is summarised below:
Despite the widespread impact of fires on the north coast, the long-term sustainable timber yield has declined by only four per cent.
There are a few key reasons that have limited the impact on overall sustainable yield. One primary reason is that Blackbutt forests which account for around 70 per cent of the long-term sustainable timber yield on the north coast were less impacted by severe fire. Blackbutt is among the most prolific and fastest growing commercial timber species on the north coast, the trees are quite resilient to fire and many timber plantations are stocked with young growing Blackbutt that also were less impacted by the 2019-20 fires. Further, in the areas that were affected, the fires were often of lower intensity or in affected forests that are tolerant to fire and will recover and continue to grow.
A higher than average impact was modelled for Spotted Gum, which is among the slower growing species and was also impacted to a greater extent by intense fire. The volume of Spotted Gum that can be produced has been modelled to decline by around 20% in the short term.
The models show that the total volume of timber produced today can be sustained over the long term. Forestry Corporation will work with its customers to discuss adjustments that may be required to account for the modelled impacts.
In comparison to the north coast, the State forests on the south coast, and in Eden and Tumbarumba were affected by more severe and more widespread fires.
About 80 per cent of the forests in this region were impacted by fire and as a result, long-term timber supply on the south coast is modelled to reduce by around 30 per cent. This arises as there are a mixture of more and less fire-tolerant species across the south coast supply area, with a varying level of tree survival depending on size, species and fire intensity. The south coast forests were impacted by a higher extent of severe fire and the forests are generally much slower growing than those on the north coast, so recovery of timber volumes in the forests will be far slower.
Due to the severe fire impact and fire sensitivity of local species, it is anticipated that many of the fire-affected trees will die or decline in quality over the coming 10 years. In many fire affected forests in this region there has already been a prolific regeneration of new seedlings. Over the next 10 years the sustainable yield model focuses on recovery of fire affected stands where timber can be recovered before the timber degrades and is unusable. This strategy is recommended both for timber production but also for silvicultural purposes by removing the degrading damaged trees and allowing better growth in the regenerating forests. This will also allow a reduced level of harvesting in unburnt and less affected forests which can continue to grow for another 10 years.
On this basis, the model assumes that timber production will remain stable over the next 10 years, after which it will reduce for the medium term before recovering to current productive capacity in the long term.
Due to the severe fire impact and fire sensitivity of the local preferred commercial species (Alpine Ash), many of fire-affected trees have already died or are rapidly declining. The full extent of the tree mortality has not yet been able to be fully mapped, however that process is underway. Once the level of tree mortality is fully mapped the sustainable yield model will be revised. It is expected this will occur in a matter of months. Short term wood supply from Tumbarumba forests is entirely focused on removal of fire killed trees. There has already been a prolific regeneration of new seedlings across fire affected stands.
How has the environmental impact of the fires been accounted for?
The sustainable yield model is an assessment of how much timber is available working in line with the strict environmental rules that regulate forestry operations. Environmental regulations are a key part of the sustainable yield model and all the areas excluded from harvesting under these regulations, such as old growth, rainforest, wildlife corridors are mapped and excluded from the calculations. Provisions are also made for retaining hollow bearing trees and other important habitat features that are required to be retained in harvesting. Approximately half the total State forest estate and large proportions of each harvest area are set aside for habitat and environmental protection, and the models only calculate the volume of timber that can be produced in compliance with these environmental rules.
How accurate are Forestry Corporation’s sustainable yield models?
Forestry Corporation uses a system known as the Forest Resource and Management Evaluation System (FRAMES). This system has been used for more than a decade and the models have been continually adjusted and improved based on input over this time. FRAMES was independently reviewed by the Auditor General in 2009, with all recommendations subsequently carried out, and more recently in 2017. A range of reports, reconciliations and reviews are available on our website.
The models are constantly recalibrated and data inputs regularly updated to account for a changes in the forest and to ensure that long term growth modelling is accurate. This includes regular measurement of inventory plots as well as assessments of both standing and felled timber to account for the rate of unseen internal defects on high quality timber production. The models also maintain a 10 per cent ‘headroom’ or margin of error.
We have a high level of confidence in both the sustainable yield models and in the accuracy of the assumptions that underpinned this sustainable yield review following the fires. An independent review has been carried out, drawing on comprehensive technical data and sensitivity analysis.
How was the sustainable yield review completed following the fires?
It is important to note that this review is an interim measure, carried out in the immediate aftermath of the fires when it was not safe to measure inventory. Due to the safety hazards in forests recently impacted by fire, a satellite based fire severity model was used to map the fire intensity across the landscape. These fire intensity maps were combined with existing inventory data to model the range of severity of fire impact across the timber resource.
While this was a newly-developed system, because of our role in both firefighting and post-fire recovery, we had the advantage of having field staff ground truth the model using our Map App and provide feedback. The assumptions and models were modified based on feedback from both ground truthing by staff and stationary photo points have provided feedback on how the forest is recovering. Work has now commenced on field inventory for our full review, which will be completed in 2023-24.
Will timber commitments be reduced as a result of this sustainable yield review?
Forestry Corporation is now beginning discussions with its customers to discuss the updated resource models and implications for ongoing timber supply. Any specific changes to supply arising from this modelling work will be discussed with the affected customers. Given Forestry Corporation has never allocated 100 per cent of the available sustainable timber yield, overall timber production on the north coast can be maintained at current levels.
We cannot maintain our existing levels of timber production on the south coast or Tumbarumba. Our long-term contracts on the south coast expired in 2020 and future contracts will reflect the reduced resource availability. In the Eden area, the modelling proposes harvesting for the first ten years in forests impacted by high severity fire to remove fire affected and degrading timber, while facilitating forest regeneration. This will produce roughly equivalent volumes to existing supply, however after this initial period supply is likely to be reduced.
How confident is Forestry Corporation in this review?
This review is an interim measure that was carried out based on the best available data in the period immediately following the fires. The model inputs included significant ground truthing, timber recovery studies and a stationary photo point project that provide a sound basis for estimating the impacts and recovery from the fires. We are already working to update the model with field assessments and inventory measurements so a robust review can be published in 2023-24.
We have around 3000 active strategic inventory plots throughout the forest as well as several hundred permanent growth plots throughout the forest. Ahead of the next review, we will be increasing our measurements of both strategic and permanent growth plots to gather detailed data on post-fire recovery. The inventory re-measurement program started in late 2020 and we are bringing on extra staff to support the increased measurement of inventory plots to inform a robust review.