Central North Island wood availability forecasts for the period 2008–2040
Wood availability forecasts for the Central North Island
Assumptions
The wood availability forecasts for the Central North Island are based on the following assumptions:
- Replanting – All area in the large-scale owners’ estate that is clearfelled is replanted (with a regeneration lag of 1 year) apart from 8000 hectares in 2006 and 2007 combined. It is assumed that 90 percent of area clearfelled in the small-scale owners’ estate is replanted.
- The area awaiting replanting as at 31 March 2006 is included as area at age 0, that is, area to be replanted in the 2006 planting season.
- Species/Regime – Area is replanted into the same species. Following harvest of old radiata pine croptypes, replanting was assumed to be in proportion to the area in young radiata pine croptypes, that is, future silviculture was assumed to reflect what is currently being applied.
The total volumes of radiata pine and Douglas-fir harvested by large and small-scale owners in 2006 and 2007 are shown in Table 1.
Table 1: Volumes harvested in 2006 and 2007
| Harvest year | Species | Large-scale owners (m3) | Small-scale owners (m3) |
|---|---|---|---|
| 2006 | Radiata pine | 7 120 000 | 524 000 |
| Douglas-fir | 266 000 | 10 000 | |
| 2007 | Radiata pine | 6 918 000 | 533 000 |
| Douglas-fir | 303 000 | 10 000 |
These harvest figures differ from roundwood removal estimates by region as reported in MAF’s statistics (2008 – http://www.maf.govt.nz). The difference is attributed to the fact that the roundwood removal estimates are derived from regional mill outputs and log export volumes; the harvest figure indicated above are from a direct survey of growers within the region. This difference indicates a net flow of logs into the region for processing or export.
Overmature stands – it was assumed that any area of radiata pine in the small-scale owners’ estate over 40 years would not be harvested. This resulted in the removal of 134 hectares.
Scenario 1 – Harvest all forest at age 28
The scenario with all forest harvested at age 28 indicates the “pure” (that is, unconstrained) availability of wood from the Central North Island. It is essentially a translation of the age-class distribution into volume. Figure 2 shows the age-class distribution of radiata pine in the Central North Island, while Figure 3 shows the wood availability. The high point at 2024 in Figure 3 occurs because of the large area (24 187 hectares) at age 10 (planted in 1996) in Figure 2.
It is worth noting the lift in the wood availability in 2008: it suggests large-scale owners have potential harvest available immediately, but are not currently planning to harvest. Therefore changing market conditions are likely to cause larger owners to depart from their stated intentions within the 2008 to 2015 period. This in turn reflects the relative maturity of the Central North Island forest industry.
Figure 2: Age-class distribution of Central North Island radiata pine – combined estate as at 1 April 2006
Figure 3: Central North Island radiata pine availability under scenario 1
Scenario 2 – Large-scale owners harvest at intentions, small-scale owners at age 30
In this scenario, large-scale owners harvest in line with their stated intentions, and small-scale owners harvest trees at age 30.
Large-scale owners
The age-class distribution of the large-scale owners’ estate (Figure 4) is reasonably uniform at least between ages 0 and 26. The area at age 0 is the area awaiting replanting as at 31 March 2006 (that is, area to be replanted in the 2006 planting season).
Figure 4: Age-class distribution of the Central North Island radiata pine estate – large-scale owners as at 1 April 2006
For this scenario the availability of wood from large-scale owners is based on stated harvest intentions for 2006 to 2015. Thereafter the availability is constrained to be non-declining with a target rotation age of 30 years. The wood availability of large-scale owners (Figure 5) is forecast to increase until it reaches 9.8 million cubic metres per year from 2016. The increase between 2015 and 2016 reflects the higher yields (cubic metres/hectare) that owners expect to get from young stands when they mature.
Figure 5: Central North Island radiata pine availability under scenario 2 – large-scale owners
The volumes shown in Figure 5 are for clearfelling only. Production thinning volumes were compared for large-scale owners in the wood availability model, with stated intentions (Figure 6). Production thinning volumes are low compared to clearfell volumes.
Figure 6: Radiata pine production thinning volumes available under scenario 2 – large-scale owners as at 1 April 2006
Small-scale owners’ estate
The age-class distribution of the small-scale owners’ estate (Figure 7) is very irregular with greater areas between ages 4 to 14 years, particularly ages 9 to 12 years (planted in 1994 to 1997), and much less area in other age-classes. The key issue is how to forecast the availability from this estate. In particular, whether the large area of younger stands will be harvested:
- at a fixed rotation age (scenario 2);
- spread over many years (scenario 3);
- spread over an intermediate number of years (scenario 4).
Figure 7: Age-class distribution of the Central North Island radiata pine estate– small-scale owners as at 1 April 2006
Combined estate
The wood availability from all owners is presented in Figure 8, with that of large-scale owners being the same as in Figure 5. In this scenario 2, all forest in the small-scale owners’ estate is assumed to be harvested at age 30. The fluctuations in the total volume harvested reflect the variation in the age-class distribution of the small-scale owners’ estate.
The large increase in volume from 2022 (Figure 8) occurs when the large areas from the small-scale owners’ estate in young age-classes are harvested. For example, the increase in 2022 results from the 3769 hectares planted by small-scale owners in 1992 (age 14 in Figure 7) being harvested at age 30 years.
Figure 8: Central North Island radiata pine availability under scenario 2 – combined estate
Fluctuations in harvest volumes of the magnitude shown in Figure 8 would be impractical because of marketing and logistics realities (for example, the immediate availability of logging crews, transport capacity, and wood processing capacity).
Scenario 3 – NDY (target rotation 30 years)
The third scenario assumes a non-declining yield, with a target rotation age of 30 years. Figure 9 indicates that when the small-scale owners’ estate is harvested to complement the large-scale owners’ estate, the total volume (radiata pine) has the potential to increase to 11.6 million cubic metres per year from 2020. The model was constrained to ensure that the total volume harvested did not increase by more than 10 percent annually.
This scenario is similar to the base case scenario adopted in the 2000 NEFD wood supply forecasts. However, it results in the small-scale owners’ estate being harvested at rotation ages that differ markedly from 30 years (Figure 10).
Figure 9: Central North Island radiata pine availability under scenario 3
Figure 10: Average radiata pine clearfell age by ownership category under scenario 3
Scenario 4 – Split NDY (target rotation 30 years)
The fourth scenario is based on a split non-declining yield, with a rotation age of 30 years. This scenario gives a forecast wood availability that is similar to scenario 3 through to 2018 (Figure 11). Wood availability increases to 12.7 million cubic metres per year from 2021 before reducing to 10.3 million cubic metres per year from 2036.
The main difference from scenario 3 is that the large area of young stands in the small-scale owners’ estate is assumed to be harvested over a shorter period of time. The total volume was modelled to be non-declining from 2007 to 2034, that is, for the current rotation. Thereafter an annual reduction of up to 10 percent was allowed before the yield was required to be non-declining for the next rotation (from 2037). As a consequence the average clearfell age for small-scale owners stays closer to the target of 30 years (Figure 12) than was the case in scenario 3.
Figure 11: Central North Island radiata pine availability under scenario 4
Figure 12: Average radiata pine clearfell age by ownership category under scenario 4
The total volume forecast for scenario 4 is broken down by log grade in Figure 13. Potential volumes from production thinning are shown in Figure 14.
Figure 13: Central North Island radiata pine availability under scenario 4 – by log product
Figure 14: Radiata pine production thinning volumes available under scenario 4
The production thinning volumes shown above largely result from the croptype allocation in the NEFD; the rise of production thinning post-2030 reflects these areas reaching maturity for the second time. Production thinning in the CNI is influenced by several factors including the profitability of the fibre-using sectors, the demands of the pulp industry, and the silvicultural regimes required to meet these demands. A key feature is that relative to clearfell volumes, production thinning volumes are likely to remain relatively small.
Scenario 5 – Target rotation age variations
Different wood availability profiles are generated if target rotation age is changed from 30 years to either 28 or 32 years (Figure 15). Because of the limitations imposed by the current age-class distribution and large-scale owners’ stated harvest intentions, it takes some time to achieve separation of average clearfell age (Figure 16).
Figure 15 shows the potential for a significant increase in the Central North Island harvest volumes. There is a range of possibilities for timing the increase and for the level of the potential harvest volume.
Figure 15: Central North Island radiata pine availability under scenario 5
Figure 16: Average radiata pine clearfell age for each target rotation age under scenario 5
Deforestation scenario
The scenarios presented assume that the recently announced liabilities for deforestation of pre-1990 forests will result in little deforestation from 2008 on. As a variation of this, an additional scenario was modelled in which:
- 50 000 hectares of area in the large-scale owners’ estate is not replanted after clearfelling from 2008 on;
- 20 percent of area clearfelled in the small-scale owners estate is not replanted after clearfelling (compared to 10 percent in the previous scenarios).
Wood availability under the deforestation scenario is compared with that under scenario 4 in Figure 17. There is limited impact until 2037.
Figure 17: Central North Island radiata pine availability under a deforestation scenario and scenario 4
Other species
Douglas-fir
The area of Douglas-fir in the Central North Island is about 23 000 hectares of which 20 000 hectares is in the large-scale owners’ estate. The age-class distribution of Douglas-fir is reasonably uniform with an average of 500 hectares in age-classes 0 to 43 years (Figure 18).
Figure 18: Age-class distribution of Central North Island Douglas-fir – combined estate as at 1 April 2006
The Douglas-fir harvest for the large-scale owners’ estate is based on intentions for 2006 to 2015 and modelled to be non-declining from 2016 on, and the harvest from the small-scale owners’ estate from 2007 on. Long-run volumes are 200 000 cubic metres per year from the large-scale owners’ estate and 230 000 cubic metres per year from the combined estate (Figure 19).
Figure 19: Central North Island Douglas-fir availability – combined estate
Contact for Enquiries
Gerard Horgan
MAF Policy
Sector Performance Policy
PO Box 1340
Rotorua
Ph: 07 921 3403
Fax: 07 921 3402
Cell: 029 921 3403
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