Indicator /

Extent and condition of native vegetation

Indicator
B4a: Extent of native vegetation

Extent: Due to the large area of conservation reserves, the ACT has extensive areas of native vegetation. Any recent native vegetation losses are estimated to be small and mainly due to changes in land use from urban development. There have also been substantial revegetation efforts to restore habitat and connectivity.

Condition & trend
  • Trending arrow Poor
  • Trending arrow Fair
  • Trending arrow Good
Data quality
Moderate
B4b: Condition of native vegetation

Condition: It was not possible to determine an overall assessment of vegetation condition for the ACT, or changes over the reporting period (2015–16 to 2018–19). Available condition assessments show an increased occurrence of dieback in the ACT, large areas of poor riparian connectivity, much vegetation outside tolerable fire intervals and vegetation dominated by early and young growth stages. However, woodlands, Natural Temperate Grasslands and secondary grasslands have shown an increase in native plant species richness suggesting an improvement in condition.

Condition & trend
  • ? Poor
  • ? Fair
  • ? Good
Data quality
Low
Indicator assessment legend
Condition
  • Poor
  • Fair
  • Good

Environmental condition is healthy across the ACT, OR pressure likely to have negligible impact on environmental condition/human health.

  • Poor
  • Fair
  • Good

Environmental condition is neither positive or negative and may be variable across the ACT, OR pressure likely to have limited impact on environmental condition/human health.

  • Poor
  • Fair
  • Good

Environmental condition is under significant stress, OR pressure likely to have significant impact on environmental condition/ human health.

  • Poor
  • Unknown
  • Good

Data is insufficient to make an assessment of status and trends.

Trend
Trending arrow

Improving

Trending arrow

Deteriorating

Stable

?

Unclear

Data quality
High

Adequate high-quality evidence and high level of consensus

Moderate

Limited evidence or limited consensus

Low

Evidence and consensus too low to make an assessment

N/A

Assessments of status, trends and data quality are not appropriate for the indicator

Background

Native vegetation is integral to ecosystem services such as the protection of biodiversity, protection of water quality and soil health, and sequestration of carbon. Declines in the extent and quality of native vegetation have profound implications for the health of the ecosystem. 

The loss of vegetation is considered to be the main threat to biodiversity in Australia. 

Historic land clearing for agriculture and urban development has produced a legacy of fragmented native vegetation in some areas of the ACT. The diversity and resilience of ecological communities relate directly to their spatial configuration, patch size, contiguity, condition and connectivity. Fragmented landscapes prevent the movement of species, limiting opportunities for mating and dispersal, and potentially creating genetic isolation. Research suggests that most animals of southern Australian woodlands and forests will not usually cross a canopy gap of more than 100 metres, and will not travel more than 1.1 kilometres from a patch of at least 10 hectares of suitable living habitat.Barrett T. and J. Love, 2012, Fine Scale Modelling of Fauna Habitat and Connectivity Values in the ACT Region, prepared for Conservation Planning and Research, EPSDD, ACT Government, Canberra

Although large-scale clearing is not an issue in the ACT, native vegetation remains under continuing pressure from urban expansion. Native vegetation in conservation areas has not been extensively cleared and is more intact than native vegetation on private land and those lands separated by urban developments. In these largely intact landscapes, vegetation communities are more likely to be resilient to natural disturbances such as fire and drought. In fragmented landscapes, native vegetation remnants are more vulnerable to natural disturbance as well as pressures arising from agriculture and residential activities. This results in the decline of vegetation, or being at risk of decline, in extent, quality and regenerative capacity. Declining vegetation quality is now a key driver of vegetation loss in the ACT. Fragmentation can also exacerbate the impacts of land use change and climate change by restricting opportunities for fauna to migrate or adapt.

Condition and trends

It was not possible to determine changes in the extent of native vegetation over the reporting period (2015–16 to 2018–19) for inclusion in this report. Nor was it possible to provide an overall assessment of vegetation condition.

The 2015 ACT State of the Environment report noted that comprehensive documented information on the condition of vegetation and the amount of clearing undertaken was lacking.Office of the Commissioner for Sustainability and the Environment, 2015, ACT State of the Environment Report 2015, ACT Government, Canberra The cumulative impact of approved clearing of vegetation had also not been documented or assessed.

These issues limit the ability to report on vegetation extent and condition changes in the ACT. However, aspects of vegetation condition assessments have been undertaken in the ACT including studies of dieback, riparian connectivity, tolerable fire intervals and growth stage, and the condition of grassland and woodland endangered ecological communities (see section on Condition of native vegetation).

Extent of native vegetation

Native vegetation losses are estimated to be small and mainly due to land use change from urban development. Urban development is likely to be an increasing pressure on native vegetation and may have major impacts on vegetation and ecosystem health, as well as the ecosystem services they provide. It is important that there is consideration of the cumulative impacts of small modifications to habitat, because these can lead to thresholds being crossed unknowingly and unintentionally for at least some aspects of vegetation and ecosystem health.

Most of the ACT’s vegetation loss has been from historic clearing and ecosystem modification for agriculture and urban development. Although there has not been a comprehensive assessment of the native vegetation extent in the ACT before European settlement, there are some examples of significant losses. For example, before European settlement, Natural Temperate Grasslands were thought to cover over 25,000 hectares or 11% of the ACT area,Gellie, N. J. H., 2005, ‘Native Vegetation of the Southern Forests: South-east Highlands, Australian Alps, South-west Slopes, and SE Corner Bioregions’, Cunninghamia, 9(2): 219–54. but today they only cover around 1,100 hectares, less than 1% of the ACT (Figure B13).

Figure B13: Current grassland extent compared with estimated pre‐European settlement grassland extent
Data sourced from: Environment, Planning and Sustainable Development Directorate.

For Lowland Box Gum Woodlands, the pre-European settlement distribution was thought to be over 47,000 hectares or 20% of the ACT area,Gellie, N. J. H., 2005, ‘Native Vegetation of the Southern Forests: South-east Highlands, Australian Alps, South-west Slopes, and SE Corner Bioregions’, Cunninghamia, 9(2): 219–54. but these woodlands now only cover some 11,500 hectares, around 5% of the ACT (Figure B14). Most of the native vegetation changes are thought to be on lowlands due to the abundance of grass and absence of dense trees for agriculture, and later for urban development. It is estimated that there has been little change in the distribution of upland vegetation types.

Figure B14: Current Box Gum Woodland extent compared with estimated pre‐European settlement Box Gum Woodland extent
Data sourced from: Environment, Planning and Sustainable Development Directorate

While the loss of native vegetation remains of concern for urban development, it is unlikely to be the largest source of native vegetation change in the ACT. Chronic degradation of habitat condition, mainly in fragmented landscapes is a significant problem in the ACT. This degradation is compounded by climate change impacts such as decreasing rainfall and higher temperatures. Such degradation has led to an increased occurrence of dieback in the ACT (see section on Condition of native vegetation).

Revegetation in the ACT

The ACT Government has undertaken extensive revegetation over the reporting period (2015–16 to 2018–19). This has been undertaken in cooperation with various organisations and programs including the Australian Government’s million Trees Project, Greening Australia, and the Australian Government’s Clean Energy Future Biodiversity Fund. The works will provide vegetation corridors, riparian restoration and bank stabilisation, woodland restoration, and post-fire rehabilitation. Restoration of habitat and connectivity increases effective habitat size and access for native species, enables migration and movement to avoid temporary stressors, and aids the recovery potential and recolonisation of degraded areas. 

Between 2015 and 2019, revegetation included planting of: 

In addition, there were revegetation activities on some 1,500 hectares of private land between 2015 and 2018, mainly through works undertaken by Greening Australia. See Community leadership in sustainability and science for more information. 

These revegetation activities will increase native vegetation extent and improve the condition of ecosystems in the future.

Condition of native vegetation

Dieback

Dieback is the gradual deterioration of health in trees, sometimes leading to tree death, and is usually caused by a combination of factors including disease and pathogens, insect attack, and additional drought and temperature stress from climate change. 

While dieback affects many species in the ACT (including Eucalyptus viminalis, E. bridgesiana and E. melliodora), recent observations have recognised a significant increase in the incidence of dieback in Blakely’s Red Gum (E. blakelyi). Dieback of Blakely’s Red Gum appears to affect any age class and is occurring across rural landscapes, urban environments and reserves within the ACT. High rates of mortality in younger trees have resulted in a lack of successful maturation across the ACT landscape. If younger trees are unable to replace the older, dying trees, the population will slowly thin out. 

A great deal of uncertainty surrounds the cause of Blakely’s Red Gum dieback in the ACT and is thought to be the result of a number of stress-inducing factors, impacts associated with climate change and reduced resilience within the landscape. The ACT Government and the University of Canberra has been undertaking research to better understand the causes and occurrence of red gum dieback in the ACT.Cowood A.L. et al., 2018, Blakely’s Red Gum Dieback in the ACT, Report to Environment, Planning and Sustainable Development Directorate, Institute for Applied Ecology, University of Canberra, Canberra.

Main findings include: 

Figure B15: Temporal condition mapping of Blakely’s Red Gum (Eucalyptus blakelyi) as at 2017.

Temporal condition mapping of Blakely’s Red Gum (Eucalyptus blakelyi) as at 2017
Source: Cowood A.L. et al., 2018, Blakely’s Red Gum Dieback in the ACT, Report to Environment, Planning and Sustainable Development Directorate, Institute for Applied Ecology, University of Canberra, Canberra.

Riparian connectivity

Decline in connectivity within riparian areas is primarily due to historic clearing of vegetation for agriculture and urban development. Low river flow conditions, climate change impacts (higher temperatures, increased drought and storm events), drought and fire also impact on riparian vegetation causing loss of habitat and increased disconnection within riparian areas. 

Riparian connectivity has been assessed for the Murrumbidgee and Molonglo Rivers in the ACT. Main findings include: 

Figure B16: Connectivity of riparian vegetation along the Molonglo River
Data sourced from: Environment, Planning and Sustainable Development Directorate Notes: Based on a proximity index which assesses the area-weighted measure of the distance between vegetation patches. This analysis uses three vegetation riparian-dependent vegetation communities: Ribbon Gum Very Tall Woodland, River She-oak Riparian Forest, and River Bottlebrush–Burgan rocky riparian tall shrubland.
Figure B17: Connectivity of riparian vegetation along the Murrumbidgee River
Data sourced from: Environment, Planning and Sustainable Development Directorate Notes: Based on a proximity index which assesses the area-weighted measure of the distance between vegetation patches. This analysis uses three vegetation riparian-dependent vegetation communities: Ribbon Gum Very Tall Woodland, River She-oak Riparian Forest, and River Bottlebrush–Burgan rocky riparian tall shrubland.
Figure B18: Connectivity of riparian vegetation along the Murrumbidgee River
Data sourced from: Environment, Planning and Sustainable Development Directorate Notes: Based on a proximity index which assesses the area-weighted measure of the distance between vegetation patches. This analysis uses three vegetation riparian-dependent vegetation communities: Ribbon Gum Very Tall Woodland, River She-oak Riparian Forest, and River Bottlebrush–Burgan rocky riparian tall shrubland.

Condition of grassland and woodland endangered ecological communities

The ACT Government has been monitoring the condition of Box Gum Woodland and Natural Temperate Grassland endangered ecological communities since 2009. Results to date show the following trends: 

Overall the long term condition is positive with Box Gum Woodland and Natural Temperate Grassland endangered ecological communities in the ACT becoming more diverse. However, it is clear that short-term variations are having an impact on grass cover and the number of exotic species. Ongoing monitoring and development of management practices will be important to maintain these important communities.

Impacts of fire on native vegetation

NOTE: The condition and trends information presented here do not include the impacts of the 2019-20 fire season which burnt extensive areas of the ACT. These fires will have a significant impact on vegetation tolerable fire intervals and growth stage.

Bushfire is an important occurrence for many native vegetation communities in the ACT. Although fire can cause a temporary loss of vegetation, fire is necessary for the regeneration and regrowth of many plant species. The appropriate fire regime to promote native biodiversity (intensity, frequency, season, extent and type of fire) varies between native vegetation communities. Changes to ecologically appropriate natural fire regimes can have significant impacts on the composition of vegetation communities and the ecosystems they support. 

The ACT’s fire regimes have changed over time due to increased human sources of ignition, the suppression of natural fire to protect human life and assets, and prescribed burning practices for the management of fuel loads (see Fire section). In addition, periods of prolonged drought and higher temperatures increase the risk of more frequent and severe fires. Climate change is expected to further influence the occurrence of bushfires in the ACT.

Tolerable fire intervals

What are Tolerable fire intervals?

Tolerable fire intervals (TFI) assess the likely ecological response of native vegetation communities to subsequent fire and are based on the requirements for sensitive plant species and key habitat elements. Assessments of TFI are based on: 

  • Minimum TFI: the minimum period of time between fires to avoid a loss of plant biodiversity. This period is based on the time it takes fire-sensitive plant species to grow to reproductive maturity and produce adequate viable seed banks. Frequent burning below minimum TFI can lead to localised loss of these fire-sensitive species, and can also prevent the development of key habitat features required by some fauna such as mature overstorey, tree hollows, and the accumulation of leaf litter and logs. 
  • Maximum TFI: the maximum period of time between fires to avoid a loss of plant biodiversity. Native vegetation communities not exposed to fire for extended periods can have reduced viability of shorter lived plant species which require fire to germinate seeds. Lack of fire may also result in a decline of key habitat features required by some fauna species such as dense mid-storey vegetation. 

Minimum and maximum TFI are ecosystem-specific and are typically longer for vegetation communities that have evolved with less frequent fire, for example those occurring in cooler and moister environments where fires are naturally less frequent and where the growth rates of plants is slower. 

It should be noted that the TFI status is only a potential issue should a large, high-severity fire occur in areas that are below minimum TFI. There is no requirement that ecosystems be within a specific TFI, only that fire outside of these thresholds be limited. To promote maximum biodiversity, a range of TFI status is required to provide different habitat resources.

In 2018, only 34% of the total area of native vegetation assessed was found to be within the required TFI to maintain vegetation communities; 53% was below minimum TFI (fire interval too short to maintain vegetation in its optimal state), 7% above the maximum TFI (fire interval too long to maintain vegetation in its optimal state), and 6% was classed as long unburnt (Figures B19 and B20).

Because over 50% of the total native vegetation assessed is below TFI, large areas of the ACT will remain outside optimal TFI irrespective of the level of prescribed burning and future fire events. This potentially places species with life cycles dependent on long inter-fire intervals at increased risk.

Figure B19: Percentage area of assessed vegetation communities by tolerable fire interval status, as at 2018.
Data sourced from: Environment, Planning and Sustainable Development Directorate Notes: Assessed using Keith Class level. Post-fire status of native vegetation communities is based on prescribed fire and bushfire history up to the end of 2018. Fire history records nominally begin in 1900 but are more reliable from 2003 onwards.
Figure B20: Distribution of tolerable fire interval status for selected native vegetation communities in the ACT, as at 2018.
Data sourced from: Environment, Planning and Sustainable Development Directorate. Notes: Assessed using Keith Class level. Post fire status of native vegetation communities based on prescribed fire and bushfire history up to the end of 2018. Fire history records nominally begin in 1900 but are more reliable in later years from 2003 onwards. Blank areas are either non-native vegetation communities or urban areas.

For the 10 native vegetation communities assessed, only 4 had 50% or more of their assessable area within the preferred TFI range (Figure B21). These are the Southern Tableland Grassy Woodlands (58%), Upper Riverina Dry Sclerophyll Forests (70%), Southern Tableland Dry Sclerophyll Forests (77%), and Tableland Clay Grassy Woodlands (89%). Five native vegetation communities had none of their assessable area within TFI, and one only has 3% within TFI. These communities had fire regimes mostly below minimum TFI, the exception being the Temperate Montane Grasslands which had 60% of the assessed area above maximum TFI. Other communities with high proportions of above maximum TFI include the Southern Tableland Grassy Woodlands (39%) and Upper Riverina Dry Sclerophyll Forests (28%).

The TFI assessment also showed the following trends:

Figure B21: Percentage area of selected native vegetation communities by tolerable fire interval status, as at 2018.
Data sourced from: Environment, Planning and Sustainable Development Directorate Notes: Assessed using Keith Class level. Post-fire status of native vegetation communities is based on prescribed fire and bushfire history up to the end of 2018. Fire history records nominally begin in 1900 but are more reliable from 2003 onwards.
Growth stage

Post-fire growth stages represent the recovery of native vegetation communities after fire and the progression from early response (re-sprouting and seed germination) to the maturation of plant species and animal populations, and eventually senescence and species turnover at longer times subsequent to fire. Each growth stage is characterised by a different structural arrangement of vegetation and may be dominated by different component species. Similarly, the faunal community supported by an area will vary as the vegetation progresses through growth stages. Biodiversity values are most likely enhanced at a landscape scale by achieving a range of growth stages within each vegetation community and across the landscape.

In 2018, the adolescent growth was the most common growth stage accounting for 44% of the total area of native vegetation communities assessed (Figures B22 and B23). The next most common growth stage was mature at 38% of the total area of native vegetation assessed, with both juvenile and senescent both accounting for 9% each. While all growth stages are represented across the ACT, the landscape is dominated by early and young stages which account for over half of the assessed vegetation communities.

Figure B22: Percentage area of assessed vegetation communities by growth stage, as at 2018.
Data sourced from: Environment, Planning and Sustainable Development Directorate Notes: Assessed using Keith Class level. Post-fire status of native vegetation communities is based on prescribed fire and bushfire history up to the end of 2018. Fire history records nominally begin in 1900 but are more reliable from 2003 onwards.
Figure B23: Distribution of growth stages for selected native vegetation communities in the ACT, as at 2018
Data sourced from: Environment, Planning and Sustainable Development Directorate. Notes: Assessed using Keith Class level. Post-fire status of native vegetation communities is based on prescribed fire and bushfire history up to the end of 2018. Fire history records nominally begin in 1900 but are more reliable from 2003 onwards. Blank areas are either non-native vegetation communities or urban areas.

For the 13 native vegetation communities assessed, 8 had 50% or more of their assessable area within juvenile or adolescent growth stages (Figure B24). Five of these communities had over 80% of their assessed area in juvenile or adolescent growth stages, including Alpine Bogs and Fens, Alpine Herbfields, Subalpine Woodlands, Southern Tablelands Wet Sclerophyll Forests, and Montane Wet Sclerophyll Forests. Only 4 vegetation communities had greater than 50% of their assessed area within the mature growth stage including Montane Bogs and Fens, Southern Tableland Dry Sclerophyll Forests, Southern Tableland Grassy Woodlands, and Upper Riverina Dry Sclerophyll Forests.

Figure B24: Percentage area of selected native vegetation communities by growth stage, as at 2018.
Data sourced from: Environment, Planning and Sustainable Development Directorate Notes: Assessed using Keith Class level. Post-fire status of native vegetation communities is based on prescribed fire and bushfire history up to the end of 2018. Fire history records nominally begin in 1900 but are more reliable from 2003 onwards.

Native vegetation growth stages across the ACT reflect TFI status, with extensive areas of the uplands being dominated by early and young growth stages. This is a result of the 2003 bushfires and the relatively slow recovery rate of many upland ecosystems. The dominance of early and young growth stages has significant implications for biodiversity, especially for fauna that require older growth stages.

The growth stage assessment also showed the following trends: 

In the longer term, conservation priority needs to focus on diversifying growth stages within and between ecosystems to maximise persistence of biodiversity. In the lowlands, this can be achieved through the ecological burning of late and mature growth stages for vegetation resilient to fire. However, in the uplands achieving growth stage diversity will require time and deliberate protection of the relatively rare older growth stages from prescribed fire and bushfire until more of the landscape reaches post-fire maturity.

Case studies