Background

Implications

Regional aspects

Assessing and measuring the current situation

Indicators

Future directions

Background

The most significant threat to natural diversity in Tasmania is the clearing of native vegetation and its replacement with another activity or land use. In relation to the level of impact upon biodiversity, the types of land clearing can be viewed along a continuum. At one end of the continuum is, for example, selective harvesting of forest where, given sufficient time, at least some of the original biodiversity values will return.

However, the greater the intensity, frequency, and area of disturbance of removal of native vegetation, the greater the probability of local flora and flora extinction. These forms of more intensive land clearance, which are generally irreversible, include plantation development, clearance of native vegetation for improved pasture and cropping, inundation, and urban growth. Clearance in general is reviewed in the Land Clearance Issue Report.

As housing becomes increasingly dispersed across the landscape, clearance for urban development also has an increasingly widespread impact on biodiversity values. However, urban development can itself be viewed along a continuum of land clearance. The impacts of land clearing depend on the disturbance intensity and frequency, and the context of the disturbance.

The actual impact of urban development varies depending on the house area relative to lot size, subdivision scale and intensity relative to remaining bushland, the actions of builders and land owners in retaining native vegetation, and approaches to management of hazard reduction for bushfires. Topography and slope also influences the landscape impacts of urban development (see Scenic Landscape Condition Issue Report).

There are undoubtedly many examples of houses in Tasmania that have a minimal footprint on the local bushland and where owners have adopted a stewardship ethic in maintaining their local environment. Covenants are used by some land owners and programs such as Land for Wildlife, Private Forests Reserve Program, and the Protected Areas on Private Land provide assistance in protecting conservation values.

At the other end of the urban development continuum, impacts generally occur irrespective of best intentions and it is unlikely that a 'bushland' subdivision can be achieved with current housing expectations and building methods (see Tolmans Hill subdivision case study). In typical subdivisions, native vegetation cover is generally lost irreversibly. In general, based on present consumer demands for housing, urban development is among the least reversible of all forms of land clearance.

Urbanisation places pressures on the natural biodiversity of an area. Urban sprawl into the bushland fringe causes the physical destruction of natural habitats, causes pollution (including nutrient enrichment), and introduces predators such as cats and dogs. Such factors push back the boundary of the natural area, sometimes to the point where there is no longer enough area to support some elements of the biota. For example, bettongs are sensitive to disturbance, and will not live in bushland that has been fragmented into small areas.

Degradation is also occurring through the collection of firewood, especially around urban centres. Even if it is only the fallen wood that is being collected, it takes away the habitat and food of many other species (e.g. fungi, insects, birds). This issue is discussed in more detail in the Firewood Collection and Usage Issue Report.

The coastal zone in Tasmania has been particularly affected by development. Many wetlands have been drained and saltmarshes destroyed either directly by development, or from the alterations and contamination by run-off from such areas. Ribbon development along the shore in particular has seriously disrupted many ecologically important sea-to-land transitions which are essential for many species, including penguins, intertidal molluscs and crustaceans.

Amongst a range of other threatening processes aside from direct clearance, weed invasion and changes to fire regimes are often cited as threats to the health of urban bushland. Many weeds are associated with disturbance but some have the capacity to invade remnant vegetation and to displace native species.

The degradation of bushland by other factors such as incremental small scale development (e.g. a water tank here, a power line there, etc.), off-road vehicle use and rubbish dumping are also important. While the impact of any one incident of these activities may seem minor and not noteworthy, it is the 'death of a thousand cuts' which cumulatively poses a huge threat to the urban bushlands of the State. The level of disturbance from these impacts is often relative to the length of bushland edge exposed to urban settlement pressures in proportion to the total area of remnant vegetation (Buchanan 1983).

Whilst fire is a natural part of the sclerophyll ecosystems of the State, the intensity and frequency of occurrence of fires influence the composition and structure of the vegetation of urban bushlands. Inappropriate fire frequency, intensity and location can result in:

• impoverishment of the native flora and fauna
• promotion of fire-tolerant and fire-promoting native
• plant species (e.g. bracken) and exotic species (e.g. gorse)
• erosion and/or landslips on sloping sites
• colonisation of bare ground and eroded sites by exotic plants.

Fire management in urban bushland is guided by the requirements of both fire ecology and fuel (hazard) management. Research has been conducted by the Tasmanian Fire Research Fund to compile fuel accumulation tables for the majority of vegetation types suitable for fuel reduction burning. These allow better targeting of areas with high fuel levels. Methods to provide protection for people living around and near urban bushland areas are being improved so that the amount of protective fuel management may be reduced in favour of habitat management. Risk assessments are used to identify the people and areas in need of the highest priority for improving both the local fuel management and local resilience to fire. Increased weed control has also made a major impact in reducing fire hazards in many areas. As managers of urban bushland, several Councils have developed fire management strategies and specific fire management plans for urban bushland areas.

The value of biodiversity in the urban setting

As places where natural processes still operate with minimal human interference, urban bushland has a range of values including:

• intrinsic value, that is its value 'in and of itself'
• habitat value as home to a range of plant and animal
• species which add to the biodiversity of the city
• scientific value for its comparison to similar ecotypes under different management regimes (i.e. agriculture, forestry, etc.)
• life support value, that is for its importance in maintaining biological systems beneficial to the community (i.e. clean air and water, erosion control, etc.) recreational and tourism value as a site for a range of informal activities such as sightseeing, walking, running, nature observation, etc.
• aesthetic value, that is for its visual delight in terms of colour, texture, form, etc.
• value to the community's 'sense of place', that is its contribution to the 'image' of the city and to people's appreciation of the uniqueness of their place of residence.

Many of Tasmania's rarest plants are contained in urban bushland areas in tips, cemeteries, road reserves and parklands. The Queens Domain in Hobart for instance, is the location for five vascular plant species which are absent from any secure reserve in the State; one species which is found only on the Domain; one species which is nationally endangered; another which is vulnerable; five vascular plant species which are considered endangered or vulnerable to extinction in Tasmania; and five vascular plant species which are rare in Tasmania (Kirkpatrick 1995).

Urbanisation's influence on vegetation clearance in Tasmania

Between 1972 and 1999 over a quarter of a million hectares of native vegetation were cleared in Tasmania. The greatest losses of major vegetation types have been in swamp forests, grasslands and grassy woodlands, coastal heathland, dry forests and wetlands. The most threatened community types now are the grasslands and grassy woodlands. The least affected types since 1803 appear to be less agriculturally productive, such as alpine vegetation, and western moorland and scrub.

While urbanisation has not resulted in the extent of clearance as some other broad-scale land use activities, Tasmania's larger urban areas are concentrated in locations containing vegetation types which have been substantially cleared, including: grasslands and grassy woodlands, coastal heathland, dry forests and wetlands. The classification of land cover for Greater Hobart and Launceston (see Land Use and Land Cover for Hobart and Launceston) gives an indication of the area of urban development which has occurred.

It was reported in the last SoE Report that the impact of urban development is indicated by the loss of remnant vegetation in an area like Boronia Hill, where rapid urban development since the early 1980s has resulted in a nearly 30% loss of vegetation (de Gryse 1994). The extent of subsequent loss of native vegetation that has occurred since this study to 2003 has not been estimated.

Implications

• The most significant threat to natural diversity in Tasmania is the clearing of native vegetation and its replacement with another activity. This applies as much in the urban context as the rural context.
• Vegetation clearing is the major threat to biodiversity and may cause species extinctions by reducing and fragmenting available habitat.
• Potential loss to eco-tourism opportunities.
• Land clearance impacts landscape aesthetics as it leads to changes in the visual landscape.
• Clearing of native vegetation may also lead to changes in ecosystem processes because less rainfall is intercepted, erosion increases, temperatures close to the ground are raised, and soil moisture is lost more rapidly.

Regional aspects

Native vegetation clearance for urbanisation is concentrated in the population growth areas of the State. This is shown in the Population Distribution and New Dwelling Completions indicators.

Assessing and measuring the current situation

The extent of the loss of urban bushland in the State is unknown. Defining what constitutes urban bushland also presents some challenges as urban development is now more extensively dispersed across the landscape. Local area assessments using historic aerial photographs to determine the loss of remnant vegetation between 1946 and the early 1990s have been made which indicate the extent of the clearance problem. These were reported in the last SoE Report (SDAC 1997), but it was not possible to update these estimates for the current report. Some other broad measures of urban vegetation condition, clearance, and land cover have been included to provide an indication of the type of changes that have occurred. However, citywide estimates of urban bushland retention and loss and integrated responses are needed. The preparation of citywide inventories of native bushland is now feasible given the availability of a complete and current aerial photographic coverage mosaic of Greater Hobart and Launceston.

Indicators

Land Use and Land Cover for Hobart and Launceston - at a glance

• Continued in depth

• According to the classification of land cover derived from satellite data in 2001, urban and suburban land cover occupies 7.9% of Greater Hobart and 9% of Launceston. 'Modified' land cover classes that can be identified from Landsat data represent 33.5% of Greater Hobart and 45% of Launceston.
   
• 'Natural' land cover classes account for 61.9% of greater Hobart and 49.6% of Launceston. The difference between Hobart and Launceston is due in part to the greater significance of agriculture, pasture and forestry activity around Launceston. The Mt Wellington Park and the Meehan Range in Greater Hobart also occupy a significant area of the Greater Hobart statistical division, contributing to the overall proportion of 'natural' land cover.
   

Native Vegetation Clearing - at a glance

• Continued in depth

• Housing completions have potentially affected 805 ha of priority forest vegetation in Hobart and 291 ha of priority forest vegetation in Launceston in the period 1992-2002. This provides a guide only to the potential impacts on priority forest vegetation through urban growth as the proportion of a land parcel cleared of native vegetation for any housing completion is unknown and will vary depending on the lot size and the attitudes of builders and owners.
   
• Nevertheless, it provides an indication of development pressure on remnant vegetation. For native vegetation remaining following housing completions-particularly large-scale subdivisions-changes in hydrology, changes to fire regimes, and the introduction of weeds can ultimately result in the loss of native vegetation.
   
• In Hobart, priority forest vegetation communities that have been potentially affected over the period 1992-2002 through housing completions include:
   
• Eucalyptus risdonii (up to 15 ha). Eucalyptus risdonii trees were cleared in October 2002 for the development of residential blocks in the Clarence municipal area.
   
• Eucalyptus tenuiramis inland forest (up to 110 ha)
   
• Eucalyptus obliqua tall forest (up to 122 ha)
   
• In Launceston, priority forest vegetation communities that have been potentially affected over the period 1992-2002 through housing completions include:
   
• Eucalyptus ovata - E. viminalis shrubby forest (up to 14 ha)
   
• Eucalyptus amygdalina forest on dolerite (up to 161 ha)
   

Population Distribution - at a glance

• Continued in depth

• There are a number of broader population trends that are relevant to the retention of urban bushland. Population decline is an issue as well as population increase.
   
• The inner city areas of the major Tasmanian urban centers reduced their share of the Tasmanian population by 10% during the period 1976-2001 from 412,300 to 456,652. Much of this change has been due to declining household occupancy rates. This has meant that inner city areas with established housing stock and infrastructure are accepting less of the overall task of housing the population.
   
• In contrast, between 1996-01, mid-size centres (1,000-19,999 people) experienced population growth of 17.9% and their share of State population increased from 21.5% to 25.5%. (ABS 1996 and 2001). However, these trends also mask some significant regional variations. The rapid growth of fringe urban centres including Old Beach, Seven Mile Beach, Dodges Ferry, and Pontville contrasts with population decline in other centres.
   
• Urbanisation has resulted in formerly separate towns being linked to major centres through the journey to work: the populations of a number of these communities that are within commuting distance to urban centres have grown rapidly as a result. Two examples are Hadspen in the north (6.4% annual growth from 1996-01) and Kingston in the south (7.3% annual growth from 1996-01).
   
• Overall, localities and villages with a population of between 200 and 999 people increased their share of population from 4.7% to 6.7%. The population of localities and villages grew by 15.5% between 1996 and 2001. During the period from 1976 to 1996, 17 centres reached the threshold of a minimum of 200 people and became classed as localities and villages for the first time. These included places such as Lewisham, Primrose Sands, and Opossum Bay in the south, and Dilston, Gawler, and Sisters Beach in the north.
   

Future directions

Tasmania Together and the RMPS

Relevant Tasmania Together goals and standards for 'Biodiversity' are listed in the linked file. The Tasmania Together Progress Board reported on progress toward targets for benchmarks set (Tasmania Together Progress Board 2003). Indicators, targets and baseline data are available in the latest Progress Report June 2003. Further information, including progress report updates, is available from Tasmania Together.

Involvement of the community, and the fair and orderly use of resources are also fundamental principles of the RMPS. The RMPS objectives have been developed to advance the principles of sustainable development.