Canterbury wood availability forecasts for the period 2007–2040
Wood availability forecasts for Canterbury
Assumptions
The wood availability forecasts for Canterbury are based on the following assumptions:
Replanting
All the area that is harvested is replanted (with a regeneration lag of one year) apart from 7000 hectares in the large-scale owners’ estate that is intended to be deforested. (This is in addition to the 2200 hectares intended for clearance and deforestation).
Areas are planted back into the same species and regime.
The area awaiting replanting as at 31 March 2005 is included as area at age 0 (the area to be replanted in the 2005 planting season).
Harvest by year
The total volumes of radiata pine harvested by large-scale owners and the estimated volumes harvested by small-scale owners in 2005–2007 are shown in Table 3.
Table 3: Volumes of radiata pine harvested in 2005–2007
| Harvest year |
Large-scale owners (m3) |
Small-scale owners (m3)1 |
|---|---|---|
| 2005 | 740 000 | 90 000 |
| 2006 | 790 000 | 90 000 |
| 2007 | 740 000 | 90 000 |
Note
1 Industry estimates of harvesting from small-scale owners ranged from 80 000 to 100 000 cubic meters per year. For the purposes of modelling wood availability it was assumed 90 000 cubic meters were harvested for the years 2005–2007.
Overmature stands
The area in the small-scale owners’ estate that was age 41 years or older (534 hectares total) was excluded on the assumption that this will not be harvested.
Scenario 1
In this scenario, all trees are harvested at age 30, indicating the “pure” (unconstrained) availability of wood from Canterbury. This means wood availability reflects the age-class distribution. Figure 2 shows the age-class distribution of radiata pine in Canterbury, and Figure 3 shows the wood availability. The low point of 30-year-old trees in 2018 in Figure 3 occurs because of the small area (1714 hectares) at age 17 (planted in 1988) in Figure 2. Conversely, the high point at 2026 (Figure 3) occurs because of the large area (6246 hectares) at age 9 (planted in 1996) in Figure 2.
Figure 2: Age-class distribution of Canterbury radiata pine – combined estate as at 1 April 2005
Figure 3: Canterbury radiata pine availability under scenario 1 (all trees harvested at age 30)
Scenario 2
In this scenario, large-scale owners harvest in line with their state intentions to 2015 and small-scale owners harvest trees at age 30.
Large-scale owners’ estate
The age-class distribution of the large scale owners’ estate (Figure 4) shows some variation in the area of age-classes. The area at age 0 is the area awaiting replanting as at 31 March 2005 (to be replanted in the 2005 planting season).
Figure 4: Age-class distribution of the Canterbury radiata pine estate – large-scale owners as at 1 April 2005
For this scenario, the availability of wood from large-scale owners is based on stated harvest intentions for 2005 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 decline initially, but increase from 2011. Their high volumes in 2005 to 2007 are partially a result of areas being harvested for deforestation.
Figure 5: Canterbury radiata pine availability under scenario 2 – large-scale owners
Small-scale owners’ estate
The age-class distribution of the small-scale owners’ estate (Figure 6) is very irregular, with over 2500 hectares in ages 8 to 13 years (planted in 1992 to 1997) and much less in all other age classes. Forecasting the wood availability from this estate depends on how the large areas in ages 8 to 13 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 Canterbury radiata pine estate – small-scale owners as at 1 April 2005
Combined estate
The wood availability from all owners is presented in Figure 7. For the large-scale owners’ estate, it is the same as in Figure 5. The entire 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 (8–13) are harvested. For example, the increase in 2022 is a consequence of the 2565 hectares planted by small-scale owners in 1992 (age 13 in Figure 6) being harvested at age 30 years.
Figure 7: Canterbury 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. However, the increase in volume in 2008 indicates the potential for an increased harvest from the small-scale owners’ estate in the near future.
Scenario 3
The third scenario indicates 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 (of radiata pine) has the potential to stay at current levels through to 2016. The potentially available volume increases to 1.1 million cubic metres per year from 2019. An extra constraint was modelled, with the total volume increasing by no more than 10 percent annually. This simulates the logistical limitations of rapidly moving to a higher production volume.
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 9).
Figure 8: Canterbury radiata pine availability under scenario 3
Figure 9: Average radiata pine clearfell age by ownership category under scenario 3
Scenario 4
The fourth scenario is based on a split non-declining yield, with a rotation age of 30 years. It gives a forecast wood availability (Figure 10) that is similar to scenario 3 initially. Wood availability increases to 1.25 million cubic metres per year from 2021 before reducing to 0.93 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 2006 to 2034; that is, for the current rotation. Thereafter an annual reduction of up to 10 percent was allowed, with the yield 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 in scenario 3 (Figure 9).
Figure 10: Canterbury 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: Canterbury radiata pine availability by log grade under scenario 4
Scenario 5
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 assumed from 2008 to 2019 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 Canterbury harvest volumes some time after 2015. However, there is a range of possibilities for both the timing of the increase and the level of the potential harvest volume.
Figure 13: Canterbury radiata pine availability by target rotation age under scenario 5
Figure 14: Average radiata pine clearfell age in Canterbury by target rotation age under scenario 5
Scenarios for other species
Douglas-fir
There are about 15 000 hectares of Douglas-fir in Canterbury. The age-class distribution of Douglas-fir is far from uniform (Figure 15). The majority of the young resource (age 10 years or younger) is in the small-scale owners’ estate.
Figure 15: Age-class distribution of Canterbury Douglas-fir – combined estate as at 1 April 2005
Results are presented in Figure 16 for a split non-declining yield (as for radiata pine, scenario 4). The Douglas-fir harvest for the large-scale owners’ estate is based on intentions for 2005 to 2015, with non-declining yield thereafter. The harvest from the combined estate is required to be non-declining through to 2049 with changes (up or down) limited to 10 percent per year.
Figure 16: Canterbury Douglas-fir availability – combined estate as at 1 April 2005
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