Central North Island wood availability forecasts for the period 2008–2040
Introduction
Scenarios for radiata pine
Five wood availability scenarios have been modelled for radiata pine in this analysis. They show a range of potential ways for harvesting the forests in the region in the future.
To ensure the scenarios used in this analysis are reasonable, they were developed in consultation with the National Exotic Forest Description (NEFD) Steering Committee, and feedback was received from major forest owners and consultants in the Central North Island wood supply region.
Unless stated otherwise calendar years have been used in this report.
Scenario 1: Harvest all forests at age 28
All owners are assumed to harvest their forests at age 28. This scenario shows the potential future harvest in any given year, based on the area of radiata pine forest that reaches the assumed rotation age in that year.
Scenario 2: Large-scale owners harvest at stated intentions, small-scale owners harvest at age 30
Large-scale owners’ wood availability is assumed to be at stated harvest intentions for 2008 to 2015. After 2015, the large-scale owners’ wood availability is modelled not to decrease. Small-scale owners are assumed to harvest trees at age 30.
Scenario 3: Non-declining yield (NDY) – target rotation 30 years
Large-scale owners’ wood availability is assumed to be at stated harvest intentions (as for scenario 2). The total wood availability of radiata pine from the region is constrained to be non-declining in perpetuity.
Scenario 4: Split non-declining yield (NDY) – target rotation 30 years
This is the same as scenario 3 except that the total wood availability of radiata pine from the region is assumed to step down from 2034 (at the end of the current rotation). Thereafter, a reduction is projected.
Scenario 5: Target rotation age variations
This is similar to scenario 4 except target rotation ages of 28 and 32 years are also modelled.
Discussion on scenarios
With the exception of scenario 1, the small-scale forest owners have been modelled separately from the large-scale owners. Future harvesting from the small-scale owners is generally less certain than for the large-scale owners.
In scenarios 1 and 2 (Figures 1A and 1B, respectively), forests owned by small-scale owners are assumed to be harvested at a fixed age – 28 years in scenario 1 and 30 years in scenario 2. In scenario 1 all forests (large and small-scale) are harvested at 28 years. These two scenarios show the “potential” availability of mature forest in any given year and directly reflect the area of forest in each age class in the Central North Island region. For practical reasons already described, it is unlikely that the future harvesting would occur like this. These two scenarios simply show the potential magnitude of harvesting under favourable market conditions in any given year.
Scenarios 3 to 5 (Figures 1C and 1D, respectively) are based on yield regulation. Under these scenarios, future harvesting is generally constrained to be non-declining, that is, each year the volume must either be the same or higher than in the previous year. Yield regulation provides a more orderly harvesting volume profile that takes into account, to some extent, logistical and market constraints.
These scenarios avoid the large year-to-year fluctuations seen in scenario 1. A fundamental property of the forests in the Central North Island (although not as pronounced as in many other regions in New Zealand) is the increased area of forests established by small-scale owners during the 1990s. Scenarios 4 and 5 allow for harvesting these forests by applying a non-declining yield constraint for the period 2006 to 2034. Then once the “bulge” of forests planted during the 1990s have been harvested, the model lets the volume decline again.
The main limitations of scenarios 3 to 5 is that log prices and other market factors are significant determinants of harvesting in any given year. When log prices increase, harvesting will generally increase. When log prices fall, the level of harvesting will generally fall. It is beyond the scope of this analysis to predict future log prices.
Figure 1 shows the sequence of models (scenarios) that are presented throughout the remainder of this report.
Figure 1: The sequence of wood availability scenarios presented in this report for radiata pine. (Scenario 5 is the same as scenario 4 except it shows wood availability profiles of varying harvesting ages)
Figure 1A – Scenario 1 example: harvest all trees at age 28
Figure 1B – Scenario 2 example: large-scale owners harvest at stated intentions, small-scale owners harvest trees at age 30
Figure 1C – Scenario 3 example: non-declining yield with target rotation 30 years
Figure 1D – Scenario 4 example: split non-declining yield with target rotation 30 years
Scenarios for Douglas-fir
One scenario is presented for Douglas-fir (all owners): this is similar to scenario 3 for radiata pine. It is based on the harvest intentions of large-scale owners for 2006 to 2015 with yield regulated in subsequent years. Target rotation age is 45 years for Douglas-fir.
Wood availability from other species has not been modelled.
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