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Environment, Planning and Sustainable Development Directorate - Environment

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Key Threatening Processes

Loss of mature native trees and lack of recruitment

Under the Nature Conservation Act 2014, the Minister for the Environment and Heritage added the Loss of mature native trees (including hollow-bearing trees) and a lack of recruitment to the List of Key Threatening Processes, following advice from the Scientific Committee, on 27 September 2018.

A submission to the Scientific Committee was made on behalf of Conservation Council ACT Region, Friends of Grasslands, Australian Native Plant Society Canberra Region, Canberra Ornithologists Group, and Field Naturalists Association of Canberra.

Mature native trees, which have developed hollows within the trunk and branches, are an important form of habitat for mammals, reptiles, bats and birds, who use the hollows to nest, raise young and shelter from predators. Hollow formation is an incredibly slow process with most hollows forming in eucalypt trees after the tree reaches 120 years old. They are formed through weather damage, branch shedding, insect attack, and advanced through modification by strong-billed native parrots like cockatoos and galahs.

Since urbanisation and land clearing began in the ACT region, there has been a dramatic decline of mature aged trees. Competition for suitable nesting hollows is fierce, and birds such as superb parrots, that migrate to the ACT each year, must work extra hard to compete with our resident parrot community for nesting hollows. Superb parrots, like many other threatened Australian birds including swift parrots, brown treecreepers and glossy black-cockatoos, are unlikely to persist in the ACT without stronger protections of hollow-bearing trees.

A Conservation Advice accompanies the listing with the priority management objective to reduce the loss of mature native trees and its impact on threatened native species and to improve recruitment of native woodland tree species across the ACT. Conservation issues and proposed management actions include:

Protection

Actions to mitigate against the loss of mature native trees include:

Restrict, as far as possible, clearing of: mature eucalypts over 50 cm diameter at breast height; mature native trees that contain nest hollows; and native trees (other than eucalypts) that have reached approximately 67% of their maximum diameter.
Promote retention of standing dead trees wherever possible.
Encourage retention of non‐mature native trees across urban and rural landscapes to ensure a future supply of mature trees and avoid lag times.

Conservation and management

Actions to promote improved health of mature native trees across the landscapes:

provide funding and support to encourage rural landholders to manage stock and control grazing to reduce compaction and accumulations of nutrients under trees to enhance recruitment and health of isolated trees
maintain connectivity of woodland tree species at a range of temporal and spatial scales

Actions to promote improved recruitment:

provide buffer plantings around isolated trees
fence off isolated remnants and trees to reduce grazing pressure
continue to fund tree replacement programs in urban areas and revegetation programs across the ACT

Survey, monitoring and research

Actions include:

continue to specifically monitor loss of mature trees across the ACT's landscapes
continue research on Eucalypt dieback in the ACT and appropriate provenance for revegetation programs under climate change

Unnatural Fragmentation of Habitats

Under the Nature Conservation Act 2014, the Minister for the Environment and Heritage added the 'Unnatural fragmentation of habitats' to the List of Key Threatening Processes (NI2019-822), following advice from the Scientific Committee, on 19 December 2019.

A nomination of the threatening process Unnatural Fragmentation of Habitat was made by the Scientific Committee and was assessed against the eligibility criteria outlined in the Nature Conservation (Key Threatening Processes Eligibility) Criteria 2016 (DI2016-256).

The Committee considered the nomination and other research on the process within the ACT and region. Evidence has been provided that the threatening process is occurring and that there has been substantial unnatural fragmentation of habitat particularly in development areas and agricultural landscapes.

'Unnatural Fragmentation of Habitat' is any fragmentation that disrupts biological processes/biological organisation and significantly increases the likelihood of extinction of flora and fauna beyond that due to natural processes.

Unnatural fragmentation applies, at different scales, to flora, fauna and ecological communities; terrestrial and aquatic species and habitats; suburban and rural areas; and reserves. It implies a loss of ecological connectivity.

A Conservation Advice (NI2019-833) accompanies the listing with the priority management objective to prevent further fragmentation and, where feasible, to improve connectivity between habitat fragments within the Australian Capital Territory.

Conservation issues and proposed management actions include:

Avoidance – It is far preferable to avoid fragmentation than to attempt to ameliorate it or recreate connectivity after a development.
Shape and edge effects – Ensure that terrestrial habitat patches are approximately circular in shape, while avoiding the creation of patches that are narrow and linear or have a convoluted outline.
Scale – Bigger is better. Avoid creating patches that are small. These will support fewer individuals of the species of interest and thus the population of that patch will be less resilient to other impacts.
Proximity – Minimize the distance between patches created. This may allow mobile individuals to move between patches, such that individuals lost to impacts on one patch may be replaced by immigration from a neighbouring patch.
Restoration – Habitat loss need not be permanent. In areas that will be disturbed during the activity but not permanently alienated, avoid disturbing soil and long-lived features (e.g. large mature trees) and plan to re-instate previous topography, vegetation etc.
Reconnection – Ideally any patches created by the activity should be re-connected via the restoration of habitat (above) but where this is not feasible, patches can occasionally be reconnected via design features tailored to the species of concern.
Plants are affected by fragmentation too – Plants can be susceptible to edge effects and may also need to “move” via the dispersal of seeds and pollen.
Barriers may be subtle – The factors that prevent movement may not be readily apparent to the human eye. The nature of a barrier depends on a range of factors such as the method of dispersal and the size and physiology of the organism.
Adaptive management – The effectiveness of any given method to improve (or maintain) connectivity is likely to be context dependent. It is important to apply an adaptive management approach, collecting data on how a method is utilized by the target species, and modifying the method where necessary to ensure its efficacy.