Southern North Island wood availability forecasts for the period 2008–2040
Wood availability forecasts for Western Southern North Island
Assumptions
The wood availability forecasts for the Western Southern North Island (SNI) are based on the following assumptions:
- Area was obtained from the NEFD as at 31 March 2006. To reflect the regime split in the harvest intentions data, 1000 hectares in the large-scale owners’ estate was transferred from the old pruned croptype into the old unpruned croptype.
- 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 area in the old pruned croptype in the large-scale owner’s estate is replanted into the unpruned croptype 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 2006–2008 are shown in Table 1. 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 consultants in the region.
Table 1: Volumes of radiata pine harvested in Western SNI in 2006 to 2008
| Harvest year | Large-scale owners (m3) |
Small-scale owners (m3) |
Total (m3) |
|---|---|---|---|
| 2006 | 426 000 | 329 000 | 755 000 |
| 2007 | 483 000 | 236 000 | 719 000 |
| 2008 | 494 000 | 269 000 | 763 000 |
For the overmature radiata pine stands still in the NEFD database, it was assumed that trees of 36 years or older will not be harvested, and therefore removed from the model:
- 431 hectares total in the large-scale owners’ estate;
- 490 hectares total in the small-scale owners’ estate.
Scenario 1 – Harvest all forest at age 30
This scenario has all areas harvested at age 30. It indicates the “pure” (that is, unconstrained) availability of wood from the Western SNI region. It is essentially a translation of the age-class distribution into volume. Figure 2 shows the age-class distribution of radiata pine in the Western SNI, while Figure 3 shows the wood availability. The low point at 2018 (in Figure 3) occurs because of the small area (1321 hectares) at age 18 (planted in 1988) in Figure 2. The high point at 2024 in Figure 3 occurs because of the large area (9674 hectares) at age 12 (planted in 1994) in Figure 2.
Figure 2: Western SNI radiata pine age-class distribution – all owners as at 31 March 2006
Figure 3: Western 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 4) shows the variation in area by age-class. On average, there is about 900 hectares in ages 0 to 28. However, there is relatively little area in ages 12 to 19. Conversely, there is a relatively large area in ages 7 to 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 4: Western 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 5) is forecast to decrease through to 2014 but then increase, reaching 475 000 cubic metres per year from 2019.
Log grade minimum small-end diameters are: Pruned 35 cm; Unpruned 20 cm; Pulplog 10 cm.
Figure 5: Western 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 6) is very irregular with over 3000 hectares in each of ages 9 to 14 years (planted in 1992 to 1997) and much smaller areas in all other age-classes. The key issue is how to forecast the availability from this estate. In particular, how will the large area in ages 9 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 6: Western SNI radiata pine age-class distribution as at 31 March 2006 – small-scale owners only
All Western SNI owners
The wood availability from all Western SNI owners is presented in Figure 7 with that of the large-scale owners’ estate 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 7) occurs when the large areas from the small-scale owners’ estate in young age-classes (9–14) is harvested. For example, the increase in 2022 results from the 4383 hectares planted by small-scale owners in 1992 (age 14 in Figure 6) being harvested at age 30 years.
The increase in volume from the small-scale owners’ estate in 2009 (shown in Figure 7) reinforces what is evident in Figure 6: that is, that there is a reasonable area that is approaching harvest age.
Figure 7: Western SNI radiata pine availability under scenario 2 – combined estate
Fluctuations in harvest volumes of the magnitude shown in Figure 7 would be impractical 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 8 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. The potentially available volume increases to 1.4 million cubic metres per year from 2020. An extra constraint was added so the total volume was not allowed to increase by more than 10 percent annually from 2008.
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 9).
Although the target rotation for the large-scale estate was nominally 30 years, the average clearfell age exceeds this. The older average ages reflect the consequences of imposing non-declining yield constraints on an age-class distribution that is far from normal.
Figure 8: Western SNI radiata pine availability under scenario 3
Figure 9: 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 2020 (Figure 10). Wood availability increases to over 1.75 million cubic metres per year from 2022 before reducing to 1.3 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 2008 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 11) than was the case in scenario 3.
Figure 10: Western SNI radiata pine availability under scenario 4
Figure 11: 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 12.
Figure 12: Western 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 13). 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 14). No increase was allowed from 2008 to 2016 for the 32-year variation in order to get separation in harvest volumes.
Figure 13 shows that there is the potential for a significant increase in the Western SNI harvest volumes. There is a range of possibilities for timing the increase and the level of the potential harvest volume.
Figure 13: Western SNI radiata pine availability under scenario 5
Figure 14: Average radiata pine clearfell age for each target rotation age under scenario 5
Other species
Douglas-fir
The area of Douglas-fir in the Western SNI is about 950 hectares (large-scale owners have 800 hectares, small-scale owners have 150 hectares). Most of this area is approaching maturity (Figure 15) and is scheduled for harvest over the next 15 to 20 years (Figure 16).
Figure 15: Western SNI Douglas-fir age-class distribution – all owners as at 31 March 2006
Figure 16: Western 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
Contact this person
