The NFPS defines old growth as forest that is ecologically mature and has been subjected to negligible unnatural disturbances such as logging, roading and clearing. The definition focuses on forests in which the upper stratum or overstorey is in the late mature to overmature growth stages.
In order to facilitate the application of this definition for the purpose of the IAP, interim old growth forest was defined as:
| Forest that has a significant proportion of the oldest discernible growth stages in its overstorey and negligible structural evidence of disturbances, using interpretation of 1:25,000 scale aerial photographs. These criteria must be interpreted within the context of the characteristics that would be expected of the latest successional stage(s) likely to be attained by the vegetation type under the unmodified disturbance regime characteristic of its site. |
In line with the precautionary principle, it permits any forest with negligible evidence of disturbances of any origin to be considered as old growth forest, and requires that the significance of discernible growth stage proportions and disturbance evidences be evaluated according to how significantly the forest structure differs from a state of ecological maturity. By specifying ecological maturity in terms of the latest successional stage(s) likely to be obtained under unmodified disturbance regimes, the definition allows for the irregularity of natural disturbance regimes. While these disturbances generally maintain forests in a non climax state, forests may progress to later stages (including climax vegetation) during unusually long intervals between individual disturbance events.
Records of forest disturbance was used to modify the outputs of API growth staging.
Forest growth stages were identified and mapped by the Broad Old Growth Mapping Project (BOGMP) using aerial photograph interpretation (API) of colour 1:25,000 photographs of varying ages. An interpretation protocol and coding system was developed and adhered to as far as practicable throughout the project. A nominal minimum polygon size of 25 ha was used to delineate growth stages.
All areas of public lands included in the IAP were classified, however, no growth staging was carried out for polygons identified primarily as : Code O non eucalypt forest (including eucalypt plantation where identified); Code R rainforest; and Code L recently logged forest.
The relative proportion of regrowth and senescent crowns formed the basis for determining growth stage classes. These elements were estimated over a polygon as a percentage of total crown cover as outlined below in Table 3.1.
Table 3.1 Key to growth stage classes and codes used in Table 3.2 and 3.3.
| Proportion of Late Mature and senescent tree crowns | ||||
| Proportion of regrowth tree crowns | A | B | C | U |
| >30% | 10-30% | <10% | unassessed | |
| t | tA | tB | tC | tU |
| s | sA | sB | sC | sU |
| e | e | e | e | e |
Note: Where regrowth exceeded 30% of the canopy cover, there was no assessment of the late mature or senescent growth stage classes
Additional tags were attached to the codes in Table 3.1 to qualify the growth stages assessed. These included:
D - insufficient detail, assessment unreliable
f - fire damaged crowns, assessment unreliable
y - logging disturbance but crowns assessable
r - continuous rainforest understorey
The API data were validated using:
(1) field checks standardised with set proformas and point to plant sampling protocols; and
(2) aerial photograph interpretation checks conducted by SFNSW which resulted in the examination of 50% of all photos in the Northern study area and 35% of all photos in the Southern study area.
On completion of API, old growth and other successional stages were defined according to the relative proportions of senescent and regrowth crowns in combination with disturbance or logging history data. The above successional stage codes were then applied across a range of environmental site qualities (see below Table 3.2). These codes were then linked by environmental site quality with forest types (see Section 3.1) specific to each major study area to enable
Table 3.2 Environmental site quality classes and allocations of API successional stage codes
| Successional Stages |
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| Interim Old Growth Forest |
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| Disturbed old forest |
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| Mature Forest |
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| Disturbed mature forest |
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| Young Forest |
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| Rainforest |
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Notes:
the determination of the proportion of old growth within each forest type (see Table 3.3).
Forest types in the following growth stages were only used where it was shown that no logging had occurred in those areas in the last 20 years (Table 3.2):
These definitional categories have only been included when it can be shown that no logging has occurred within these forest areas in the last 30 years. Logging history data supplied by SFNSW in the form of the Wood Resources Study (see Section 2.6) was used in all study areas except Northern where records compiled by NPWS were used.
The BOGMP mapped the growth stages of forests on most of the lands subject to the IAP. These include:
Table 3.3 The allocation of forest and vegetation types to environmental site quality classes for the four study areas.
Environmental Site Quality
Forest/ High Moderate High / Low Very low
Vegetation moderate
Types (atypical)
Northern 36, 47, 37, 38, 39, 49, 53, 30, 40, 41, 42, 61, 65/1,
Study Area 48, 51 45, 46, 52, 71, 150 55, 62, 64, 67, 65/2, 92/2,
54, 56, 60, 68, 70/1, 70/2, 97, 105, 106,
Forest Types 76, 81, 87, 72/1, 72/2, 74/1, 107, 111, 115,
101, 151, 152, 74/2, 80, 82, 83, 117, 119, 124,
153, 154, 155, 84, 85, 92/1, 93, 126, 129, 130,
163/1, 167, 96, 98, 122, 131, 138, 141, 142,
168 140, 144, 159, 161, 172, 207
160, 163/2, 164,
170, 177
Central 47 36, 37, 39, 49 41, 62, 64, 67, 65, 100, 105,
Study Area 46, 52, 60, 70, 72, 74, 74, 106, 113, 117,
82, 87 83, 84, 85, 115, 126, 128, 130
Forest Types 119, 121
Southern 81, 83, 88, 90, 77, 78, 60, 9, 4, 147, 23, 135, 142,
Study Area 82, 95, 97, 67, 92, 151, 114, 157, 119, 143, 134, 144,
56, 94, 62, 65, 149, 34, 120, 121, 122, 130, 133, 145,
Vegetation 47,49 50, 53, 10, 36, 156, 129 150, 161
Units 44, 45, 48, 55, 14, 15,
42, 43, 80, 152, 153,
20, 113, 13, 19, 22, 24,
38, 39, 41, 71, 29, 33,
148, 159, 5, 6, 7, 11,
85, 86, 2, 25, 96, 100,
107, 110, 150, 155, 118,
111, 116, 124, 125, 137,
138, 141, 123, 131, 132,
127
Eden Study 9, 10, 16 2, 3, 22, 25, 24, 36, 54,
Area 5, 11,12, 13, 14, 15, 26, 28, 30, 31, 56, 58, 59
17, 18, 19, 20, 21, 27, 32, 33, 34, 37,
Vegetation 29, 35, 41, 42, 43 44, 45, 46, 47,
Types 48, 49, 50
For the IAP, State forest, most national park and some vacant Crown land and leasehold lands (where identified by the FPA as likely to have significant areas of old growth) have been mapped for old growth. Exceptions were national parks in the Central Study Area and all tenures considered in the Tumut Study Area, where the late inclusion precluded old growth mapping. For the purpose of the IAP, it is assumed that no significant areas of old growth forest remain on private property or unassessed VCL and leasehold lands.
The Commonwealth proposed the following broad criteria for the inclusion in a reserve system of old growth which is a critical successional stage within forest types:
(1) Wherever practicable, all, but at least 90 per cent, of old growth in the following categories of forest types/communities should be included in the CAR reserve system
(2) For forest types with 10 to 25 per cent old growth, ... varying proportions of old growth should be protected in reserves, varying inversely from 90 per cent to 60 per cent according to the proportions of old growth in the extant distribution. At least 40 per cent of the protected old growth should be in dedicated conservation reserves.
(3) For forest types with more than 25 per cent old growth in extant distributions, 60% of that old growth be protected, with at least 40 per cent in dedicated conservation reserves."
The BOGMP identified a range of successional stages within each forest type including: old growth, disturbed old growth, mature, disturbed mature and young forest (see Table 3.2). For the IAP, the old growth successional stage was considered in isolation to all other successional stages which were pooled into the one category (i.e. other successional stages within that forest type).
Reservation targets for the old growth successional stage were set in line with the Commonwealth criteria, such that:
This was achieved using the formula:
OGT% = -2(x%) +110
where:
OGT% = old growth target (%)
x% = old growth proportion of extant distribution expressed as a percentage.
and,
No targets were set for other successional stages. Instead, where possible, other successional stages were addressed within the existing forest type target in the following way:
Figure 3.3 Old growth reservation for forest types with 0-25% old growth in the extant distribution.
A total of 3.46 million ha were mapped across a range of tenures in the four broad study areas. Tables showing forest type, old growth distribution and