Interpretation of the Forecasts
This section discusses issues to consider when using the wood supply forecasts.
The forecasts presented in this report are based solely on the available supply of wood. There has been no attempt to match this supply to the international demand for forest products. The current outlook suggests that the future harvest from New Zealand's planted forests is most likely to fall between the base cut and late cut scenario in the short to medium term. Market demand, labour and capital capacity constraints may make it difficult to lift the level of harvest as quickly as the early or base cut scenarios indicate is possible. The increase in available wood supply from New Zealand needs to be set within an international context particularly within the Asia-Pacific trading region. The report "Asia-Pacific Forestry Sector Outlook Study" (FAO, 1998) provides an overall description of the wood demand and supply situation for the Asia-Pacific region. This report is available on the FAO Internet site: www.fao.org/forestry/fon/fons/outlook/Asia/apfsos/apfsos-e.stm .
ALTERNATIVE HARVEST STRATEGIES
Three forecast scenarios based on clearfell age are presented in this report. The primary constraint in all the scenarios is non-declining yield. Non-declining yield means the forecast harvest volume can not diminish over time: the volume must either go up or remain constant. In reality other harvest strategies are possible. In three regions (Northland, Auckland and Nelson & Marlborough) the early cut scenario is virtually identical to the base cut scenario. The reason for this is that in the early cut model it was not possible to reduce the clearfell age to 25 years and maintain non-declining yield. An alternative harvest strategy, which has not been modelled, would be to remove the non-declining yield constraint and allow larger volumes to be harvested earlier in the forecast horizon and reduced later in the horizon.
Harvesting at younger ages reduces the long-term sustainable yield. If a harvest strategy tending towards the early cut forecast was adopted, it would not be possible to switch back to a harvest strategy with an older clearfell age and still maintain a non-declining yield.
EFFECT OF HARVEST AGE ON WOOD PROPERTIES
The aspirations of forest owners and the intended end-use of harvested timber will direct forest management and hence the age at which stands are harvested. For instance, untended stands could be grown on shorter rotations if the planned end use was for fibreboard production. However pruned stands could be grown on longer rotations if the intention was to produce large diameter pruned logs suitable for veneer or clearwood end uses.
The wood supply forecasts show that the outcome of forest owners selecting a harvesting strategy tending towards the early cut scenario would more rapidly increase yield but with a consequent reduction in clearfell age. In the early cut scenario the average clearfell age decreases from 33 to 26 years between 2000 and 2015. In three regions (East Coast, Hawkes Bay and Southern North Island) the clearfell age drops as low as 23 years at times over the forecast horizon.
The physical properties of radiata pine logs from younger stands are different from those of logs produced from older stands. Within a region younger logs are generally lower in density and strength.
The forecast for each of the clearfell age scenarios reaches a plateau, where the annual recoverable volume becomes reasonably constant indefinitely. Table 3 (page 8) summarises these levels and the years these levels are reached.
The new planting scenarios do not reach a steady plateau, since new areas of forest are continuously established over the forecast horizon. The new planting scenarios initially track the base cut forecast, before beginning to diverge from 2010. This increase in the level of harvest before the newly established areas reach maturity is possible for two reasons; (a) increased volumes from production thinning are available, and (b) anticipated future yields from the new plantings can be allocated to the current sustainable harvest level. The new planting forecasts begin to rise significantly above the base cut forecast from 2022.
The wood supply forecasts in this report show the potential sustainable wood supply if the planted forests in New Zealand are managed to maximise long-term yield within the constraints of non-declining yield. They are based on sets of assumptions that are predominantly static through time. In reality, forest management practices, forest estate size and forest estate characteristics will change.
New forecasts should be undertaken when forest management practices and forest estate characteristics change. For instance, yield tables will be revised by forest owners to reflect changes in growth rates or stem quality characteristics. Genetic improvement in radiata pine may require quite significant changes to the forecasts over the next 10 years.
Although detailed forecast yields are presented over a 40-year horizon the forecasts will become less accurate through time.
It should be recognised that the harvest from New Zealand's planted forests is not regulated by the artificial forecasting constraints and regional boundaries used in this study.
Planted forests are managed to maximise the benefits to the enterprise that owns them. Each enterprise has its own harvest strategy based on the planted forest resources it owns and current market conditions. Changes resulting from these harvest strategies in forest resource characteristics, such as the age structure, feed back directly into the future available wood supply.
The primary driving constraint used in these forecasts is the non-declining yield constraint. At least one major company has not adopted this as an operating strategy. Other forest owners may choose to accept sustainable fluctuations rather than rigid adherence to non-declining yield regulation.
The forecasts contained in this report are essentially resource-based forecasts of the level of harvest attainable given the assumptions on yields, areas and harvesting constraints. This is not a prediction of how companies will manage the cut from their forests, nor is it a prescription for how their cut should be managed.
