Otago and Southland Wood Availability Forecasts for the Period 2007–2040
Wood availability forecasts for Southland
Southland Region
The Southland region has a plantation resource of 87 800 hectares, spread across three territorial authorities – Gore, Invercargill City and Southland District. The majority of the resource is concentrated in the Southland District, with 82 700 hectares (1 April 2006).
Assumptions
The wood availability forecasts for Southland 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.
− 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 age 0 (the area to be replanted in the 2005 planting season).
• The total volume of radiata pine harvested in 2005 and 2006 was 507 000 and 527 000 cubic metres respectively (MAF estimate).
• The total volume of Douglas-fir harvested in 2005 and 2006 was 15 000 and 19 000 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 175 hectares (aged 31 to 40 years).
Scenario 1
In this scenario, all trees are harvested at age 30. This modelling approach views the Southland wood flow as unconstrained (or pure); meaning that wood availability reflects the age-class distribution of the resource. Figure 17 shows the age-class distribution of radiata pine in Southland, and Figure 18 shows the wood availability. The 2021 low point in wood availability (Figure 18) occurs because of planting conditions in 1991. These plantings were aged 14 in the 2005 age-class distribution (Figure 17). Conversely, the 2024 high point in wood availability (Figure 18) occurs because of the large area planted in 1994, aged 11 in Figure 17.
Figure 17: Age-class distribution of Southland radiata pine – combined estate as at 1 April 2005
Figure 18: Southland radiata pine availability under scenario 1 – combined estate
Scenario 2
In this scenario, large-scale owners’ harvest in line with their intentions, and small-scale owners harvest at age 30.
Large-scale owners’ estate
The age-class distribution of the large-scale owners’ estate (Figure 19) shows a variable area in each age-class. The area at age 0 is the area awaiting replanting as at 31 March 2005 (to be replanted in the 2005 planting season).
Figure 19: Age-class distribution of the Southland radiata pine estate – large-scale owners as at 1 April 2005
For this scenario the availability of wood from large-scale forest 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 volume available from large-scale owners (Figure 20) is forecast to fluctuate around 300 000 cubic metres per year until 2016, before increasing to over 400 000 cubic metres per year from 2019.
Figure 20: Southland radiata pine availability under scenario 2 – large-scale owners
Small-scale owners’ estate
The age-class distribution of the small-scale owners’ estate (Figure 21) is very irregular, with over 1500 hectares in ages 10 to 13 years (planted in 1992 to 1995) and aged 7 (planted in 1998). Plantings have been significantly lower in all other age-classes. The key issue is how to forecast the availability from this estate. In particular, will the large areas in ages 7 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 21: Age-class distribution of the Southland radiata pine estate – small-scale owners as at 1 April 2005
Combined estate
The wood availability from all owners in Southland is presented in Figure 22. The large-scale owners’ resource is shown as the base load, and the data mirrors Figure 20. 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 22) reflects the maturing of the small-scale owners’ estate. For example, the increase in 2022 is a consequence of the 1638 hectares planted by small-scale owners in 1992 (aged 13 in Figure 21) being harvested at age 30 years. The spike in 2024 is caused by the harvest of 3636 hectares planted by small-scale owners in 1994 (aged 11 in Figure 21).
Figure 22: Southland radiata pine availability under scenario 2 – combined estate
Volume fluctuations of the magnitude shown in Figure 22 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 is based on non-declining yield, and a target rotation age of 30 years. Figure 23 indicates that there is the potential for the total radiata pine volume (from the combined large owner and small-scale owner estate) to increase to over 850 000 cubic metres per year from 2023. However it also indicates that wood availability is only 450 000 cubic metres per year from 2007 to 2016. The drop from 2006 to 2007 is a consequence of the current level of harvest from the small-scale estate not being sustainable over the next 10 years.
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 24).
Figure 23: Southland radiata pine availability under scenario 3 – all owners
Figure 24: Average radiata pine clearfell age in Southland under scenario 3 – by ownership category
Scenario 4
The fourth scenario is based on a split non-declining yield, with a target rotation age of 30 years. This scenario gives a similar forecast of wood availability to scenario 3 through to 2023. Thereafter, there is an increase to over 1 million cubic metres per year from 2025 (Figure 25), with a subsequent reduction to 750 000 cubic metres per year from 2037 on. 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. As a consequence, the average clearfell age for small-scale owners stays closer to the target of 30 years than in Scenario 3 (Figure 26).
Figure 25: Southland radiata pine availability under scenario 4 – all owners
Figure 26: Average radiata pine clearfell age in Southland under scenario 4 – by ownership category
The harvest volumes forecast under scenario 4 are broken down by log grade in Figure 27.
Figure 27: Southland radiata pine availability by log product 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 28). To get separation in harvest volumes from 2006 onwards, the annual increase allowed for the 32 year rotation (over the 2005 to 2019 period) was limited to 1 percent, rather than 10 percent.
Figure 28: Southland radiata pine availability by target rotation age under scenario 5
Figure 29: Average radiata pine clearfell age in Southland by target rotation age under scenario 5
Scenarios for other species
Douglas-fir
The age-class distribution of Douglas-fir in Southland is far from uniform (Figure 30). Large areas of Douglas-fir were established from 1995 to 2003. This age class structure imposes challenges for yield regulation.
Figure 30: Age-class distribution of Southland Douglas-fir - combined estate as at 1 April 2005
The Douglas-fir harvest for the large-scale forest owners’ estate is based on harvesting intentions for the period 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 31 clearly shows the potential for an increase in the supply of this species in the long term. Over 50 percent of the volume between 2025 and 2032 will come from production thinning.
Figure 31: Southland 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
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