Land targets
The land forms the interface between the Earth’s crust and its atmosphere. Its physical form – the landscape – includes rock, soil, vegetation, water and structures built by people. ACT landscapes consist of rugged timbered mountains in the south and west (uplands), and hill and plains country in the north and north-east. Approximately 60% of the territory is hilly or mountainous. The flatter northern plains and hill country contain most of the urban landscape.
- The uplands occur at altitudes of 800 m to 1912 m above sea level, lying mainly on erosion-resistant, ancient sedimentary rocks and granite. Flooding has deposited sediments in many of the river valleys.
- The rolling or undulating hills country generally lies between 600 m and 900 m above sea level, across moderately weathered rocks in the north-eastern part of the territory and along the eastern parts of the Murrumbidgee corridor in the south.
- The plains are in the north of the ACT at between 550 m and 650 m above sea level. They occur on readily weathered rocks and on stream sediment surrounding isolated hills and ridges of erosion-resistant rock such as Black Mountain and Mount Ainslie.
ACT soils are highly variable, with most being infertile. The main soil types are lithosols, gradational soils and duplex soils.
- Lithosoils are characterised by shallow stony profiles overlying rocky parent material in the south and west of the ACT. These soils are nutritionally poor and on steeper slopes are liable to erosion when native vegetation is removed or they are mechanically disturbed.
- Gradational soils have profiles that show a gradual increase in clay content with depth. They are common in the Cotter River catchment and in the north-east, and are the principal soil types under the limestone plains of old Canberra. These soils are deep and relatively fertile. Those on the north-east plain are relatively resistant to erosion. Gradational soils on
steeper slopes erode if the land is cleared. - Most of the ACT and its settled areas have duplex soils, characterised by a distinct change in particle size at a depth of 15–30 cm. The topsoil is light in colour, coarse textured and often sandy. It is fragile and, if cultivated or overgrazed, becomes hard setting and relatively impermeable so that rain runs off and can form erosion gullies. Subsoils tend to be reddish or yellow clays that may shrink and swell as water content changes, sometimes damaging infrastructure. These soils often contain sodium salts, so that they are dispersible if exposed. Much of the turbidity of Canberra’s lakes after heavy rain is caused by erosion of these soils.
Land capability and soil health
The physical attributes of the land (landform, geology and soils) determine its capability to accommodate various kinds of land uses that in turn impact on natural processes such as nutrient movement, plant growth, and surface and subsurface flow of water. The capability of land to support a given type and intensity of use without its ability to carry out these natural processes being damaged must be taken into account when developing planning and management strategies, assessing developments, and managing land in accordance with current best practice.
The land is a dynamic and rich biological system. Soils contain a living biomass of microbial populations including fungi and bacteria that play a critical role in cycling nutrients, establishing plants and forming soils, and in geochemical transformations. Decayed living material forms the organic matter that supports the microbial populations, stores and buffers nutrient concentrations, influences water storage, and is a major factor in determining overall soil structure and erodability.
In addition, the carbon stored in soil is becoming a key issue in mitigating climate change – soil holds more carbon as plant organic matter than plants and atmosphere combined. Even when it is burnt much of the soil’s carbon is still held as charcoal. Carbon is also retained in the fibrous root mass of grasslands. In future, land capability assessment will likely need to take account of stored carbon.
The impacts of dryland, irrigation and urban salinity are evident across many rural areas in Australia, including the major catchments surrounding the ACT that provide a watershed to the Murrumbidgee River. Although salinity is not currently considered a major problem within the ACT, this situation may change, particularly with continued urban development and the likely adoption of water re-cycling at both the centralised and decentralised scale. The Council will adopt a watching brief in relation to the need for a specific salinity target and re-evaluate the need for a target in five years’ time.
Land capability: identify land capability so that land use can be matched to capability; better understand the ‘cumulative impact’ of long periods of altered land use
Soil fertility: ensure that soils do not lose their fertility
Acid soils: identify areas of acid soils
Salinity: understand the risk of salinity and reduce recharge wherever possible by increasing perennial vegetation in potentially saline catchments; reduce the amount of salt entering rivers from sewage treatment
Erosion: maintain adequate ground cover to reduce erosion by either wind or water; ensure a minimum of erosion occurs on land being developed for urban or other infrastructure
Land use: ensure universal adoption of best practice
Climate change: identify opportunities for mitigating climate change by storing more carbon in the soil; modify land use practices in order to retain resilient landscapes as the impacts of climate change unfold.
Land use and land management in the ACT
Land-use practices pose the major threat to our soils. Longterm improvement in soil health will depend on matching land capability to land use through a systematic approach.
Prior to the arrival of Europeans, land in the ACT supported a diversity of healthy, resilient natural landscapes. Over the past 200 years, it has been increasingly required to support activities – grazing, cropping, logging, forestry plantation and urban development – that have modified the land.
In the most modified areas, the cumulative impact of clearing, cultivation and urban development have induced a range of local and off-site impacts on soil health and landscape functioning, including:
- reduced permeability, structural stability, nutrient cycling and moisture, and carbon holding capacity
- increased soil erosion
- localised salinity and acidity problems and
- impairment of hydrological functioning.
Despite these impacts, with some exceptions, land uses in the ACT are not inherently inconsistent with land capability. Perhaps the single most significant exception has been the development of forestry plantations on lands with highly erodable soils and on slopes above 20 degrees (Environment ACT 2006c).
Urban land health
The city of Canberra now occupies only marginally less land than rural leases in the ACT. Current and projected population growth, and the already planned greenfield expansion, means that urban use will soon become the second most dominant land use after conservation reserves. Urban development (with all its associated infrastructure) is one of the most intensive forms of development that can be imposed on land and can dramatically alter natural ecological and hydrological functioning at a local, subcatchment and whole-of-catchment scale.
Best practice urban development and management aims to mimic natural ecological and hydrological processes so that the ecosystem services they provide are minimally disrupted. Best practice ensures that:
- strict controls over erosion during times when the land is most vulnerable (e.g. on building sites or after drought)
- vegetation cover on developed land is adequate, appropriate and resilient to large-scale natural events (e.g. fire or storms) and smaller-scale disruptions (e.g. prevention of driving on verges) and
- vegetation cover on buffer land (particularly at the urban boundary/interface) is preserved.
This target challenges the ACT to achieve and maintain a leading Australian standard for urban land health. Achieving this target depends on:
- developing better methods of measuring urban land health
- measuring current status and identifying priority areas for action and
- developing options for better urban land management and
supporting their uptake.
Rural land health
Approximately 20% of ACT land is used for rural production. While intensive agriculture and horticulture is undertaken in some areas, the dominant rural land use is grazing. Grazing enterprises face challenges at three levels:
- addressing the legacy of the past
- accommodating the likely future impacts of climate change and
- maintaining enterprise viability.
Significant progress has been and is being made by most landholders to improve soil health and landscape functioning. However, further improvement is needed to address the cumulative impacts of rural activity and improve catchment health.
Climate change is also likely to place increased pressure on leaseholders and land management authorities to ensure more widespread and consistent application of best practice as a buffer against more extreme weather events. However, climate change may also bring new opportunities. For example, rural land might be a focus for carbon sequestration activities such as:
- planting more trees
- restoring and extending native grasslands
- assimilating organic waste from urban areas and
- capturing environmental and economic benefits of increased soil carbon.
Healthy soils are a fundamental part of the landscape and the intention of the rural land health target is to increase the viability of sustainable land management in the ACT. The key indicators of soil health are soil pH, soil carbon and hydrological connectedness. Inadequate data means a quantitative baseline cannot yet be established for this target. The proposed actions include developing and applying the required measures of rural land health. Improvements in rural land health will be driven by education, incentives and regulation through land management agreements.
centre of Canberra.
