Otago and Southland Wood Availability Forecasts for the Period 2007–2040
Wood availability forecasts for Otago
Otago Region
The Otago region has a plantation resource of 127 900 hectares, spread across five territorial authorities – Central Otago, Clutha, Dunedin City, Queenstown-Lakes and Waitaki. The majority of the resource is concentrated in the Clutha District, with 83 200 hectares (1 April 2006).
Assumptions
The wood availability forecasts for Otago are based on the following assumptions:
• All areas are replanted, with a regeneration lag of one year. Replanting is as follows:
− Large-scale forest owners – all areas are planted back into the same species and regime apart from about 7000 hectares of radiata pine that is replanted into Douglas-fir.
− Small-scale forest owners – all areas are planted back into the same species and regime.
Based on a recent deforestation survey (2006 Deforestation Intentions Survey, Bruce Manley, 2006), the Otago and Southland regions are likely to experience a relatively low rate of deforestation between 2006 and 2020 (about 3900 hectares). This level of deforestation is not sufficient to warrant changes to the forecast models.
• 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).
• The total volume of radiata pine harvested in 2005 and 2006 was 925 000 and 895 000 cubic metres respectively (MAF estimate).
• The total volume of Douglas-fir harvested in 2005 and 2006 was 66 000 and 94 000 cubic metres respectively (MAF estimate).
• It was assumed that any radiata pine forest in the small-scale owners’ estate that was aged over 40 years would not be harvested. The area in the small-scale owners’ estate that was aged 31 to 40 years was reviewed. Local knowledge was used to determine whether the forest was still standing and, if so, whether or not it was likely to be harvested. As a result of this exercise, the area data was reduced by 212 hectares (aged 31 to 40 years).
Scenario 1
In this scenario, all trees are harvested at age 30. This modelling approach views the Otago wood flow as unconstrained (or pure); meaning that wood availability reflects the age-class distribution of the resource. Figure 2 shows the age-class distribution of radiata pine in Otago, and Figure 3 shows the wood availability. The 2019 low point in wood availability (Figure 3) occurs because of planting conditions in 1989. Just 1167 hectares were planted in the 1989 season. These plantings were aged 16-years in the 2005 age-class distribution (Figure 2). Conversely, the 2024 high point in wood availability (Figure 3) occurs because of the large area planted in 1994 (6380 hectares), aged 11 in Figure 2.
Figure 3 indicates that wood availability does not have the potential to increase markedly for about 15 years.
Figure 2: Age-class distribution of Otago radiata pine – combined estate as at 1 April 2005
Figure 3: Otago 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 stated intentions and small-scale owners harvest their holdings at age 30.
Large-scale owners’ estate
The age-class distribution of the large-scale owners’ estate (Figure 4) shows that there is about 2000 hectares in most age-classes up to age 28. 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 Otago 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 be relatively static through the forecast period. Although there is replanting of some radiata pine area into Douglas-fir, the volume of radiata pine can be sustained. The higher yield (cubic metres per hectares) anticipated for younger stands and replanted stands compensates for the reduced area in radiata pine.
Figure 5: Otago 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 2000 hectares in ages 9 to 13 years (planted in 1992 to 1996) and much less in all other age classes. The key issue is how to forecast the wood availability from this estate. In particular, will the large areas in ages 9 to 13 be harvested:
• at a fixed rotation age (Scenario 2);
• spread over many years (Scenario 3); or
• spread over an intermediate number of years (Scenario 4).
Figure 6: Age-class distribution of the Otago radiata pine estate – small-scale owners as at 1 April 2005
Combined estate
The wood availability from all owners in Otago is presented in Figure 7. The large-scale owners’ resource is shown as the base load, and the data mirrors Figure 5. The fluctuation in the total volume harvested reflects the variation in the age-class distribution of the small-scale owners’ estate, and the assumption that this estate is harvested at age 30.
The large increase in harvest volume after 2022 (Figure 7) reflects the maturing of the small-scale owners’ estate. For example, the increase in 2022 is a consequence of the 3269 hectares planted by small-scale owners in 1992 (aged 13 in Figure 6) being harvested at age 30 years.
Figure 7: Otago 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. There would not be enough harvesting capacity (harvesting crews and equipment) to cut all the volume available during the peak period, and it would be difficult to get short-term sales contracts to cover this volume.
Scenario 3
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 (of radiata pine) only increases slightly through to 2017. The potentially available volume increases to 1.5 million cubic metres per year from 2021. 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: Otago radiata pine availability under scenario 3 – all owners
Figure 9: Average radiata pine clearfell age in Otago under scenario 3 – by ownership category
Scenario 4
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 2021 (Figure 10). Wood availability increases to 1.7 million cubic metres per year from 2022 before reducing to 1.25 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 not to decrease between 2006 and 2034, that is, for the current rotation. Thereafter an annual reduction of up to 10 percent was assumed, 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 than in scenario 3 (Figure 11).
Figure 10: Otago radiata pine availability under scenario 4 – all owners
Figure 11: Average radiata pine clearfell age in Otago under scenario 4 – by ownership category
The harvest volumes forecast under scenario 4 are broken down by log grade in Figure 12.
Figure 12: Otago radiata pine availability by log product under scenario 4 – all owners
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). The results indicate that the potential to markedly increase the wood harvest is limited prior to at least 2013.
Figure 13: Otago radiata pine availability by target rotation age under scenario 5 – all owners
Figure 14: Average radiata pine clearfell age in Otago by target rotation age under scenario 5 – all owners
Scenarios for other species
Douglas-fir
The age-class distribution of Douglas-fir in Otago is far from uniform, as shown in Figure 15. Large areas of Douglas-fir were established from 1997 to 2000, mainly by large-scale forest owners. This imposes challenges for future yield regulation. To illustrate this, the wood availability graph for Douglas-fir has been extended to 2060 (rather than 2040 as in all other graphs).
Figure 15: Age-class distribution of Otago Douglas-fir – combined estate as at 1 April 2005
The Douglas-fir harvest for the large-scale owners’ estate is based on intentions for 2005 to 2015. From 2015 to 2049, clearfell volume is constrained to be non-declining – both for large-scale owners and for the combined estate. Clearfell volumes can change by 100 000 cubic metres per year for the large-scale owners’ estate and by 150 000 cubic metres per year for the combined estate.
Figure 16 clearly shows how large-scale owners dominate the potential supply of this species. About 50 percent of the volume between 2027 and 2032 comes from production thinning.
Figure 16: Otago Douglas-fir availability – combined estate (volumes include production thinning as well as clear-fell)
Contact for Enquiries
Parnell Trost
Policy Analyst
MAF Policy
Natural Resources Group
PO Box 5648
Dunedin
Ph: 03 951 4705
Fax: 03 951 4711
Cell: 029 951 4705
Contact this person
