Northland wood availability forecasts for the period 2008–2040
February 2009
Wood availability forecasts for the Northland region
Assumptions
The wood availability forecasts for the Northland region are based on the following assumptions:
- Replanting - All area is replanted (with a regeneration lag of 1 year).
- The area awaiting replanting as at 31 March 2007 is included as area at age 0: that is area to be replanted in the 2007 planting season.
- Species/regime - Area is replanted into the same regime except that during the period 2007 to 2026:
- Only 25 percent of area harvested in the large-scale owners' estate from pruned stands is replanted into the young pruned croptype, with the other 75 percent replanted into the young unpruned croptype.
- Only 75 percent of area harvested in the small-scale owners' estate from pruned stands is replanted into the young pruned croptype, with the other 25 percent replanted into the young unpruned croptype.
These changes reflect the intention of owners, particularly large-scale, to prune less in the future.
Table 1: Volumes harvested in 2007 and 2008 for radiata pine in the Northland wood supply region
| Harvest year | Large-scale owners (m3) | Small-scale owners (m3) | Total (m3) |
|---|---|---|---|
| 2007 | 1 767 000 | 256 000 | 2 023 000 |
| 2008 | 2 053 000 | 240 000 | 2 293 000 |
Overmature stands - Forest aged 36 years or older (785 hectares in total) and half the area in the small-scale estate between ages 31 and 35 (703 hectares) was removed from the model, on the assumption that this area will not be harvested (or has already been harvested).
Scenario 1 - Harvest all forest at age 30
The scenario with all forest harvested at age 30 indicates the "pure" (unconstrained) availability of wood from Northland. It is essentially a translation of the age-class distribution into volume. Figure 2 shows the age-class distribution of radiata pine in the Northland, while Figure 3 shows the wood availability. The low point at 2021 (in Figure 3) occurs because of the small area (1711 hectares) at age 16 (planted in 1991) in Figure 2. The high point at 2016 in Figure 3 occurs because of the large area (12 075 hectares) at age 21 (planted in 1986) in Figure 2.
Figure 2: Age-class distribution of Northland radiata pine - combined estate as at 1 April 2007
Figure 3: Radiata pine availability in the Northland region under scenario 1
Scenario 2 - Large-scale owners harvest at intentions, small-scale owners harvest 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 total area included in the model for large-scale owners is 138 000 hectares. The age-class distribution of the large-scale owners' estate (Figure 4) is far from normal (uniform). There are relatively large areas between ages 20 and 25 (planted between 1982 and 1987). The area at age 0 is the area awaiting replanting as at 31 March 2007 (that is, area to be replanted in the 2007 planting season).
Figure 4: Age-class distribution of the radiata pine estate in the Northland region - large-scale owners as at 1 April 2007
For this scenario the availability of wood from large-scale owners is based on stated harvest intentions for 2007 to 2015. Log grade minimum small end diameters are: Pruned 35 cm; Unpruned 20 cm; Pulplog 10 cm.
A reduction is permitted between 2015 and 2016. 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 rapidly and exceed 3.2 million cubic metres per year from 2012 before reducing to 3.0 million cubic metres per year from 2016. The reduction between 2015 and 2016 reflects the age-class distribution; that is, the spike in 1982 to 1987 planting with less area planted in subsequent years. This reduction is consistent with supplementary information provided by large-scale owners on harvest intentions from 2016 to 2025.
Figure 5: Radiata pine availability in the Northland region under scenario 2 - large-scale owners
Small-scale owners’ estate
The age-class distribution of the small-scale owners’ estate (Figure 6) is irregular with over 2000 hectares in each of ages 8 to 15 years (planted in 1992 to 1999) and less area in all other age-classes. The key issue is how to forecast the wood availability from this estate. In particular whether the large area in ages 8 to 15 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 6: Age-class distribution of the radiata pine estate in the Northland region - small-scale owners only
Combined estate
The wood availability from all owners is presented in Figure 7 with that of large-scale owners the same as in Figure 5. In scenario 2, 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 (planted from 1992) are harvested. For example, the increase in 2022 results from the 2436 hectares planted by small-scale owners in 1992 (age 15 in Figure 5) being harvested at age 30 years.
Figure 7: Radiata pine availability in the Northland region under scenario 2 - combined estate
Fluctuations in harvest volumes of the magnitude shown in Figure 6 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 over 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 2015 on.
This scenario is similar to the base case scenario adopted in the "National Exotic Forest Description, National and Regional Wood Supply Forecasts 2000", (Ministry of Agriculture and Forestry, 2000). The increase in average rotation age for the large-scale owners'’ estate to 35 years (Figure 9) is a consequence of the non-normal age-class distribution (Figure 4). However the scenario results in the small-scale owners’ estate being harvested at rotation ages that differ markedly from 30 years (Figure 9).
Figure 8: Radiata pine availability in the Northland region 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 age of 30 years. This scenario gives a forecast wood availability that is similar to scenario 3 through to 2019 (Figure 10). Wood availability increases to 4.7 million cubic metres per year from 2023 before reducing to 3.4 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 constrained 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 11) than was the case in scenario 3.
Figure 10: Radiata pine availability in the Northland region 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: Radiata pine availability in the Northland region under scenario 4, by log product
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 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). For the 32-year variation, the harvest from the large-scale owners’ estate in 2009 to 2015 was reduced to 90 percent of harvest intentions.
Figure 13 shows the potential for a significant increase in the Northland harvest volumes. There is a range of possibilities for timing the increase and for the level of the potential harvest volume.
Figure 13: Radiata pine availability in the Northland region under scenario 5
Figure 14: Average radiata pine clearfell age for each target rotation age under scenario 5
Contact for Enquiries
Policy Adviser
Pastoral House
MAF Policy
PO Box 2526
Wellington 6140
NEW ZEALAND
Fax: +64 4 894 0741
Contact this person
