Southern North Island wood availability forecasts for the period 2008–2040
Wood availability forecasts for Eastern Southern North Island
Assumptions
- The wood availability forecasts for the eastern side of the SNI wood supply region are based on the same assumptions as the western side:
- All areas are replanted after harvesting, with a regeneration lag of one year, except for 10 percent of the area in the small-scale owners’ estate which is assumed to be deforested.
- 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 and management regime – Areas are replanted into the same species and regime except that:
- all Douglas-fir in the large-scale owners’ estate is replanted to radiata pine following harvest;
- 25 percent of pruned area in the small-scale owner’s estate is replanted into the unpruned croptype following harvest.
The total volumes of radiata pine harvested by large- and small-scale owners in 2006 to 2008 are shown in Table 2. The large-scale owners’ returns are based on the harvest intentions data supplied to MAF. The small-scale owners’ estimates are based on feedback from the main consultants in the region.
Table 2: Volumes of radiata pine harvested in Eastern SNI 2006 to 2008
| Harvest year | Large-scale owners (m3) |
Small-scale owners (m3) |
Total (m3) |
|---|---|---|---|
| 2006 | 138 000 | 165 000 | 303 000 |
| 2007 | 285 000 | 305 000 | 590 000 |
| 2008 | 335 000 | 265 000 | 600 000 |
- For overmature radiata pine stands that appeared in the NEFD database it was assumed that the following will not be harvested, and therefore removed from the model:
- trees of 41 years or older (59 hectares total) in the large-scale owners’ estate;
- trees of 36 years or older (406 hectares total) in the small-scale owners’ estate.
Scenario 1 – Harvest all forests at age 30
This scenario has all areas harvested at age 30. It indicates the “pure” (that is, unconstrained) availability of wood from the eastern region. It is essentially a translation of the age-class distribution into volume. Figure 17 shows the age-class distribution of radiata pine in the eastern side, while Figure 18 shows the wood availability. The low point at 2019 (in Figure 18) occurs because of the small area (413 hectares) at age 17 (planted in 1989) in Figure 17. The high point at 2026 in Figure 18 occurs because of the large area (5455 hectares) at age 10 (planted in 1996) in Figure 17.
Figure 17: Eastern SNI radiata pine age-class distribution – all owners as at 31 March 2006
Figure 18: Eastern SNI 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 19) shows the variation in area by age class. There is relatively little area in ages 16 to 19. Conversely there is a relatively large area in ages 10 and 11. 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 19: Eastern SNI radiata pine age-class distribution as at 31 March 2006 – large-scale owners only
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 and can increase by no more than 10 percent per year. The wood availability of large-scale owners (Figure 20) is forecast to decrease through to 2013 but then to increase, reaching 375 000 cubic metres per year from 2024.
Figure 20: Eastern SNI radiata pine availability under scenario 2 – large-scale owners only
Small-scale owners
The age-class distribution of the small-scale owners’ estate (Figure 21) is very irregular with over 2000 hectares in each of ages 7 to 14 years (planted in 1992 to 1999) and a much smaller area in all other age classes. The key issue, as with the western side, is how to forecast the availability from this estate. In particular, will the large area in ages 7 to 14 be harvested:
- at a fixed rotation age (scenario 2); or
- spread over many years (scenario 3); or
- spread over an intermediate number of years (scenario 4).
Figure 21: Eastern SNI radiata pine age-class distribution as at 31 March 2006 – small-scale owners only
All Eastern SNI owners
The wood availability from all owners is presented in Figure 22, with that of the large-scale owners being the same as in Figure 20. 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 22) occurs when the large areas from the small-scale owners’ estate in young age classes (7–14) is harvested. For example, the increase in 2022 results from the 3543 hectares planted by small-scale owners in 1992 (age 14 in Figure 21) being harvested at age 30 years.
The increase in volume from the small-scale owners’ estate in 2009 (shown in Figure 22) reinforces what is evident in Figure 21: that there is a reasonable area that is approaching harvest age.
Figure 22: Eastern SNI radiata pine availability under scenario 2 – combined estate
Fluctuations in harvest volumes of the magnitude shown in Figure 22 would not be practical because of marketing and logistics realities (immediate availability of logging crews, transport capacity, and wood processing capacity).
Scenario 3 – Non-declining yield (target rotation 30 years)
The third scenario assumes a non-declining yield, with a target rotation age of 30 years. Figure 23 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 substantially, to 1.2 million cubic metres per year from 2022. An extra constraint was added so the total volume was not allowed to increase by more than 10 percent annually from 2006 on.
This scenario is similar to the base case scenario adopted in the National Exotic Forest Description, National and Regional Wood Supply Forecasts 2000 (MAF 2000). However, it results in the small-scale owners’ estate being harvested at rotation ages that differ markedly from 30 years (Figure 24).
Although the target rotation for the large-scale estate was nominally 30 years, the average clearfell age exceeds this. During the period 2006 to 2015 this occurs because the model is based on harvest intentions – large-scale owners are intending to harvest at average ages older than 30 years. This reflects the higher rotation age of the Juken resource. Thereafter the higher average ages reflect the consequences of imposing non-declining yield constraints on an age-class distribution that is far from normal.
Figure 23: Eastern SNI radiata pine availability under scenario 3
Figure 24: Average radiata pine clearfell age by ownership category under scenario 3
Scenario 4 – Split non-declining yield (target rotation 30 years)
The fourth scenario is based on a split non-declining yield, with a rotation length of 30 years. This scenario gives a forecast wood availability that is similar to scenario 3 through to 2021 (Figure 25). Wood availability increases to over 1.5 million cubic metres per year from 2024 before reducing to 1.1 million cubic metres per year from 2037.
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 volume 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 26) than was the case in scenario 3.
Figure 25: Eastern SNI radiata pine availability under scenario 4
Figure 26: 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 27.
Figure 27: Eastern SNI radiata pine availability under scenario 4 – by log type
Scenario 5 – Target rotation age variations
Different wood availability profiles are generated if the target rotation age is changed from 30 years to either 28 or 32 years (Figure 28). 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 29). No increase was allowed from 2008 to 2016 for the 32-year variation in order to get separation in harvest volumes.
Figure 28 shows that there is the potential for a significant increase in the Eastern SNI harvest volumes. There is a range of possibilities for timing this increase and the level of the potential harvest volume.
Figure 28: Eastern SNI radiata pine availability under scenario 5
Figure 29: Average radiata pine clearfell age for each target rotation age under scenario 5
Other species
Douglas-fir
The area of Douglas-fir in the Eastern SNI is about 660 hectares (large-scale owners have 560 hectares, small-scale owners have 100 hectares). Most of this area is approaching maturity (Figure 30) and is scheduled for harvest over the next 5 years (Figure 31).
Figure 30: Eastern SNI Douglas-fir age-class distribution – all owners as at 31 March 2006
Figure 31: Eastern SNI Douglas-fir availability – all owners
Contact for Enquiries
Policy Adviser
Pastoral House
MAF Policy
PO Box 2526
Wellington 6140
NEW ZEALAND
Fax: +64 4 894 0741
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