Auckland 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. These scenarios show a range of potential ways for harvesting the forests in the region in the future.
The scenarios were developed following consultation with the National Exotic Forest Description (NEFD) Steering Committee and feedback from interested parties who own the forests in the Auckland region, to ensure they were reasonable.
The scenarios include only radiata pine. Unless otherwise stated, calendar years have been used in this report.
Scenario 1: Harvest all forests at age 30
The estate of all owners is assumed to be harvested at age 30. This scenario shows the potential future harvest in any given year, based on the area of radiata forest that reaches 30 years of 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 2007 to 2013, thereafter the availability is regulated. From 2014 to 2017 total volume was modelled to not exceed the 2013 level. From 2018 on it was constrained to be non-declining. The estate of small-scale owners is assumed to be harvested 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 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 constrained to be non-declining for the current rotation (through to 2034). Thereafter a reduction is permitted.
Scenario 5: Target rotation age variations
This is similar to scenario 4 except that target rotation ages of 28 and 32 years are also evaluated.
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 latter.
In scenarios 1 and 2 (Figures 1A and 1B), forests owned by small-scale owners are assumed to be harvested at a fixed age of 30 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 Auckland region. For practical reasons already described, it is unlikely that 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) are based on yield regulation. Under these scenarios, future harvesting is generally constrained to be non-declining, that is, each year the volume harvested must either be the same or higher than 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 Auckland region (as in many other regions in New Zealand) is the large 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 has been harvested, the model lets the volume decline again.
The main limitations of scenarios 3 to 5 is that market factors such as log prices are significant determinants of harvesting in any given year. When log prices increase, harvesting will generally increase and vice versa. 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 the availability profiles of varying harvest ages).
Figure 1A – Scenario 1 example: harvest all trees at age 30
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
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