What the results tell us for Tumbarumba
During the current reporting period the majority of land in Tumbarumba Shire was under landuse types compatible with the land capability class. Minor salinity problems were apparent within the shire, but no new data were available on the extent of soil erosion or soil acidity over the same period.
Drought, wildfire, forestry activities and land uses not suited to land capabilities had the potential to cause erosion in the shire during the current period, although no data were available on their actual impact. Vegetation vigour in the shire was the lowest in August 2000 and in January and August 2003 following a period of below-average rainfall for the area.
Sustainability of landuse
See also: Landuse
The majority of land in Tumbarumba Shire was under landuse types compatible with the land capability class (see Table 1). About 2% of the shire had mapped landuses which were not suited to land capabilities and thus had the potential to cause erosion.
Of the 25% of the shire under grazing, some 93% of the land was within its capability to be used for that purpose. The remainder of the grazing lands were in areas with a high erosion risk if cleared, but may support limited clearing; the Department of Natural Resources (DNR—formerly Department of Land and Water Conservation) recommends that these areas remain timbered or revegetated in order to reduce the high risk of soil degradation.
Of the 0.1% of the shire under mixed farming, some 84% of the land was within its capability to be used for that purpose. The remainder of these lands were in mainly in areas with a high erosion risk if cleared, but may support limited clearing; the Department of Natural Resources (DNR—formerly Department of Land and Water Conservation) recommends that these areas remain timbered or revegetated in order to reduce the high risk of soil degradation.
Of the 0.3% of the shire under cropping, some 90% of the land was not suitable for regular cultivation. Poor suitability of these lands for regular cultivation may be partially due to climatic variables as well as erodibility. Potential impacts of this may include low crop yields or, in more steeply undulating terrain, erosion.
Of the 138 hectares of the shire under horticulture, about 31 hectares (22%) of the land was not suitable for regular cultivation. Poor suitability of these lands for regular cultivation may be partially due to climatic variables as well as erodibility. Potential impacts of this may include low crop yields or, in more steeply undulating terrain, erosion.
Of the 2% of the shire under private timber plantations, about 16% of the land was within land capability class VII. The area of these lands under land capability classes VII has a high erosion risk if cleared, and although much of the timber production forests within the state occur on these lands, they are not necessarily suited to forestry operations; the Department of Natural Resources recommends that these areas remain timbered.
|Landuse||Land Capability Class|
|Lands suitable for regular cultivation||Lands suitable for grazing—occasional cultivation||Lands suitable for grazing—no cultivation||Other lands|
Source: see About the data
Types of land degradation
The only data available on erosion extent in Tumbarumba Shire are derived from surveys carried out between 1985 and 1992 (see tables 2 and 3). These surveys indicated about 90 kilometres of gully erosion and about 60 kilometres of streambank erosion were present in the shire at that time (see Table 2), as well as extensive areas of moderate to minor sheet erosion (see Table 3).
Just under 35% of the gully erosion measured between 1985 and 1992 was classed as severe to extreme, and most gullies were less than 3 metres deep (Table 2). It is considered that most erosion gullies in Australia would have formed soon after the native vegetation was removed, and although their length has since stabilised, they are continuing to contribute sediment loads to streams (Hughes and Prosser 2003), i.e. they are continuing to deepen. In NSW overall, Edwards and Zierholz (2001) estimated that accelerated erosion rates were 10–50 times the natural rates.
|Extreme gully erosion||3 to 6m deep||6|
|1.5 to 3m deep||14|
|less than 1.5m deep||2|
|Extreme gully erosion total||22|
|Severe gully erosion||1.5 to 3m deep||8|
|less than 1.5m deep||1|
|Severe gully erosion total||9|
|Moderate gully erosion||1.5 to 3m deep||10|
|less than 1.5m deep||11|
|Moderate gully erosion total||21|
|Minor gully erosion||1.5 to 3m deep||7|
|less than 1.5m deep||30|
|Minor gully erosion total||37|
|Streambank erosion||3 to 6m deep||2|
|1.5 to 3m deep||21|
|less than 1.5m deep||36|
|Streambank erosion total||59|
Source: Department of Infrastructure, Planning and Natural Resources data from 1985 to 1992
|Major erosion type||Degree / type||Hectares|
|soil debris avalanche||1|
|Rill erosion||severe rill erosion||155|
|moderate rill erosion||260|
|minor rill erosion||99|
|Sheet erosion||severe sheet erosion||872|
|extreme sheet erosion||110|
|moderate sheet erosion||11,879|
|minor sheet erosion||146,665|
Source: Department of Infrastructure, Planning and Natural Resources data from 1985 to 1992
Some erosion may have occurred within the shire during the current reporting period due to the 2003 and 2004 droughts.
No areas of salt affected land were mapped within Tumbarumba Shire by DNR between 1985 and 1992. Salinity mapping within NSW, undertaken by the DNR between 2000 and 2005, indicated the shire had about 6 hectares of land in the early phases of dryland salinity. This apparent increase in salt affected area may reflect improved data collection methods rather than a real change on the ground.
About 23% of surface soils within the Tumbarumba Shire were classed as strongly acid (pH 3.5–5.5) in 2002 by the Department of Land and Water Conservation (now the Department of Natural Resources) (DLWC, 2002b). These soils are scattered throughout the shire, but predominantly occur within agricultural lands in the north. Although many soils in high rainfall areas are naturally acid, the level of acidity in agricultural areas may be partially due to application of nitrogenous fertilizers, removal of produce, and build up of soil organic matter (Upjohn et al. 2005). In addition, about 24% of the shire's soils were classed with a high to critical risk of soil acidification (DLWC, 2002a). This included soils in agricultural areas between Rosewood and Kahncoban that were classed as slightly acid but had a high to critical risk of soil acidification.
Impacts of soil acidity can include reduced crop yields, poor establishment of or failure of perennial pastures, permanent degradation of soil if acidity leaches to deeper soils, increase in soil erosion and siltation and recharge of aquifers leading to dryland salinity (Upjohn et al., 2005).
Causes of land degradation
Climatic conditions, natural events such as wildfires, and human activities all influence levels of land degradation. Drought conditions accompanied by overgrazing or cultivation may lead to loss of effective groundcover, leaving soil vulnerable to erosion by wind and water. Drought breaking rain may also cause erosion and can make up about 90% of the total soil loss in an area in a 20–30 year cycle (DPI 2005). Logging and fire in forested lands can significantly alter erosion rates in the short term. Atkinson (1984) measured rates up to 62 tonnes/hectare/year after bushfires, while Wallbrink et al. (2002) measured 101 tonnes/hectare/year after forest harvesting.
Drought and vegetation condition
The majority of Tumbarumba Shire falls within the Hume Rural Land Protection Board area. The shire suffered drought between January and November 2003 and between April and June 2004 (see Table 4). In addition, the majority of the shire suffered drought in December 2002.
|Months||Seasonal Conditions||Portion of RLPB|
|July 2000—May 2001||Satisfactory||Entire shire|
|Eastern part of the shire (about 80%)|
Western part of shire (about 20%)
|July 2001||Marginal||Entire shire|
|August 2001—April 2002||Satisfactory||Entire shire|
|Majority of shire (about 90%)|
Northern part of shire (about 10%)
|June—July 2002||Marginal||Entire shire|
|August—November 2002||Marginal||Entire shire|
|Northern part of shire (about 20%)|
Majority of shire (about 80%)
|January—November 2003||In drought||Entire shire|
|December 2003—January 2004||Satisfactory||Entire shire|
|Majority of shire (about 95%)|
North western part of shire (about 5%)
|March 2004||Marginal||Entire shire|
|April—June 2004||In drought||Entire shire|
Source: Department of Primary Industries, NSW (2006)
The vigour of vegetation in Tumbarumba Shire during the reporting period (see Figure 1) was lowest in late August 2000 and in late January and late August 2003. During the six months leading up to April 2003, about 27% of the shire experienced conditions as bad as the worst 5% of years on record with respect to vegetation vigour (i.e. a 1 in 20 year drought). In the six months leading up to April 2004, about 12% of the shire suffered these conditions. This coincides with drought declarations for the shire (see Table 4).
In the six months leading up to October 2002, about 29% of the shire experienced rainfall in the lowest 5% of years on record. The shire experienced below-average rainfall for most of the reporting period with the most prolonged dry spell occurring between March 2002 and May 2003. The lack of rainfall during this period and the resultant decline in vegetation vigour in the following months may have exacerbated land degradation within the shire.
* Vegetation vigour index: 0 = worst; 1 = best. The index was measured three times a month (i.e. early, mid and late); Source: see About the data
At least 196,090 hectares of land within the shire (about 45% of the shire) were affected by fire (predominantly wildfire) during the reporting period, of which about 131,500 hectares was of moderately high to very high severity. It occurred predominantly within Kosciuszko National Park east of the shire, mostly in steep wooded terrain. Although no data were available on the actual impacts of these fires on land degradation within the shire, the following points are relevant.
- Soil loss, erosion and sedimentation may have been minimal in areas where the wildfire was mostly of low to very low severity.
- Drought conditions at the time of the wildfire and exposure of water repellent soils in the area burnt may have increased runoff and erosion. If a water repellent soil layer is present below the soil surface, the first rainstorms following a severe fire may result in rills eroding soil material down to that layer (Prosser and Williams 1998).
- The occurrence of high intensity rains immediately following a wildfire or in landscapes with unstable soils due to wildfires may increase soil washoff, soil slumping and streambank collapse (CRCCH 2006). However, areas subject to low severity burns in the January 2003 wildfire in the shire may not have experienced complete loss of vegetation, the remaining cover providing a mitigating effect for potential erosion and runoff events, and allowing water infiltration during post-fire high intensity rainfall events (SCS 1986).
About 15% of Tumbarumba Shire is covered by timber production forests, primarily State-owned forests. This includes about 9,800 hectares of predominantly agricultural land converted to pine plantations of which 1,200 was converted during the current reporting period. It is not known what impact forestry operations within the shire had on land condition during the current reporting period, but the following points are relevant.
- Depending on factors such as soil type, slope and rainfall frequency and intensity, soil loss and sediment deposition in streams can result during the site preparation and harvesting stages of plantation and forestry operations, although these impacts have been shown to decrease over time (Croke et al. 1999; Croke 2004).
- Roads are the main sediment sources in timber production forests. As road densities tend to be higher in plantation than in hardwood forests, there is greater potential for soil loss and sediment yield from plantations (Croke 2004).
- Land degradation caused by native forest harvesting and plantation activities can be reduced if best management practices are applied. These may include leaving native vegetation buffer strips along streams, siting roads appropriately in relation to topography and streams, minimising soil disturbance and ensuring good design of road drainage (Croke et al. 1999).
Three confirmed and thirteen potentially contaminated sites were recorded within Tumbarumba Shire (see Contaminated sites). It is unknown what impact these areas have on land degradation.
What is being done to improve land condition?
Tumbarumba Shire is predominantly located within the Murray and Murrumbidgee Catchment Management Authority (CMA) areas established under the NSW Catchment Management Authorities Act 2003. Catchment blueprints were prepared by the catchment management boards which preceded the CMAs. These blueprints support the improvement of salinity and soil health. The Murray Catchment Blueprint (Murray Catchment Management Board 2002), completed during the current reporting period, includes a range of management actions to reduce soil loss from cropping and grazing areas through improved land management and to identify and remediate eroded areas. The Murrumbidgee Catchment Blueprint (Murrumbidgee Catchment Management Board 2003), also completed during the current reporting period, includes a range of management actions to restore and improve the sustainability and viability of soil and land management practices and reduce the impacts of salinity in the catchment area.
An Australia-wide intergovernmental agreement on a National Action Plan for Salinity and Water Quality was introduced in December 2000. Following on from this NSW signed a bilateral agreement with the Commonwealth in May 2003 to pave the way for the development of salinity and water quality action plans in priority regions around the state.
Total expenditure on land salinity under the National Action Plan for Salinity and Water Quality within the Murray Catchment since the commencement of funding under this program (April 2001) to March 2004 totalled about $236,300 for the catchment (Commonwealth of Australia 2005). A further $463,900 was budgeted for regional investments in land salinity and soil condition, but none of this had been spent as at March 2004.
Total expenditure on land salinity and soil condition under the National Action Plan for Salinity and Water Quality within the Murrumbidgee Catchment since the commencement of funding under this program (April 2001) to March 2004 totalled about $1,760,400 for the catchment (Commonwealth of Australia 2005). A further $2,932,250 was budgeted for regional investments in land salinity and soil condition, but none of this had been spent as at March 2004.
The expended funding was targeted to (Commonwealth of Australia 2005):
- development and implementation of best management practices for dryland cropping systems
- establishment of agroforestry for groundwater interception
- establishment and improved management of perennial pastures to enable persistence of groundcovers and control land degradation, particularly dryland salinity
- establishment and maintenance of saline perennial pastures for salinity control at priority sites
- implementation of the Grain and Graze program
- profitable animal production from perennial pastures
- benchmarking and understanding soil acidity to better manage acidity, sodicity and structure.
It is not known what proportion of the above funding was expended, or which of these activities were undertaken, within the shire.
The NSW Salinity Strategy, prepared in August 2000 (DLWC 2000), aims to provide guidance to slow the rate of increase in salinity in the period 2000–2010. Tools to do this include developing salinity targets for end of catchments and undertaking research regarding salinity processes, impacts on ecosystems, social and economic impacts and landuse systems which minimise or allow the use of affected lands (DLWC 2000). As part of this strategy, salinity hazard mapping was undertaken for the state during the current reporting period. Over the same time in the Murray and Murrumbidgee catchments, biodiversity benchmarks were trialed and data collected to assist in developing benchmarks for salinity control and carbon sequestration, while a catchment scale salt balance model was applied to the Murrumbidgee catchment (DIPNR 2005) (see Salinity).
Community groups, council and/or other organisations undertook various projects during the reporting period that enhanced land condition in the shire; including restoration of priority erosion sites in the Upper Murray catchment which was funded through an Environmental Trust Grant in 2001–02. Other nationally funded activities undertaken during the reporting period in the Murray and Murrumbidgee Catchment Management Authority areas (DIPNR 2004) may also have enhanced land condition in the shire.
Other activities undertaken to enhance native vegetation may also help to enhance land condition (see Ecological communities for outlines of some of these projects).
About the data
The Department of Natural Resources (DNR—formerly Department of Land and Water Conservation) provided the following data.
- Erosion, salinity (polygon features) and gully erosion (linear feature) data collected as part of the Erosion—Landuse mapping undertaken between 1985 and 1992. Due to the length of the data collection period and a number of different field surveyors, the data may vary with respect to how erosion and salinity were classified across the landscape.
- Data from salinity mapping undertaken between 2000 and 2005.
- Land capability data.
The Office of the Commissioner for the Environment intersected the land capability data (provided by DNR) with the spatial landuse mapping developed for the Australian Capital Region state of the environment report to assess potential conflicts between landuse and land capability within the shire.
Normalised Difference Vegetation Index (NDVI) data were provided by Agrecon as a measure of vegetation vigour across the shire. In addition to these data, Agrecon provided data on the percentage of the shire less than the 5th percentile with respect to rainfall and NDVI in 6-month periods between April and October within the reporting period. These months were chosen to reduce any noise associated with snowfall in the winter months.
Monthly drought maps were sourced from the Department of Primary Industries (DPI—formerly Department of Agriculture) website http://www.agric.nsw.gov.au/reader/drt-area?picQuant=100. DPI prepares the drought maps from information provided by the 48 Rural Lands Protection Boards around NSW, rainfall details from the Bureau of Meteorology and reports from DPI's regional staff. Drought classification of an area takes into account a review of the area's historic rainfall records, pasture availability, climatic events such as frosts, and seasonal factors such as pasture growing seasons (DPI 2006).
The surface soil pH and soil acidification hazard mapping was provided by the Department of Natural Resources. This mapping was undertaken in 2002 by the then DLWC for the 2002 NSW State of the Environment Report. Surface soil acidity and soil acidification hazard were mapped for agricultural lands within NSW and was derived from (sometimes limited) point data in some areas and extrapolated for each soil landscape unit. Mapping scale is large and only give a broad representation of surface soil pH and soil acidification hazard at a local government area scale.
Atkinson, G (1984) Soil erosion following wildfire in a sandstone catchment, paper presented at the A.S.S.S.I. National Soils Conference, Brisbane, 13–18 May 1984, cited in Lu, H, Prosser, IP, Monn, CJ, Gallant, JC, Priestley, G and Stevenson, JG (2003) Predicting sheetwash and rill erosion over the Australian continent, Australian Journal of Soil Research Vol. 41, 1037–1062, viewed 3 May 2006, http://palaeoworks.anu.edu.au/pubs/AustJSS03.pdf.
Commonwealth of Australia (2005) National Action Plan for Salinity and Water Quality and Natural Heritage Trust Regional Programs Report 2003–04, Departments of the Environment and Heritage and Agriculture, Fisheries and Forestry, viewed 18 April 2005, http://www.nrm.gov.au/publications/regional-report/03-04/.
Cooperative Research Centre for Catchment Hydrology (2006) Bushfires and Hydrology: Background—Other Physical Changes Due to Fire, Cooperative Research Centre for Catchment Hydrology, viewed 3 May 2006, http://www.catchment.crc.org.au/bushfire/background_otherchanges.html.
CRCCH—see Cooperative Research Centre for Catchment Hydrology
Croke, J (2004) Forest Harvesting Activities and Water Quality: A New Approach to and Old Problem, in Croke, J, Takken, I and Mockler, S, Erosion in Forests: Proceedings of the Forest Workshop—March 2004, Cooperative Research Centre for Catchment Hydrology, Technical Report 04/10 December 2004, viewed 3 May 2006, http://www.catchment.crc.org.au/pdfs/technical200410.pdf.
Croke, J, Wallbrink, P, Fogarty, P, Hairsine, P, Mockler, S, McCormack, B and Brophy, J (1999) Managing Sediment Sources and Movement in Forests: the Forest Industry and Water Quality, Cooperative Research Centre for Catchment Hydrology, Industry Report 99/11, November 1999, viewed 3 May 2006, http://www.catchment.crc.org.au/pdfs/industry199911.pdf.
Department of Infrastructure, Planning and Natural Resources, NSW (2004) 2003/04 Combined NSW Catchment Management Authorities Annual Report, Volume 1: CMA Activities and Achievements, Department of Infrastructure, Planning and Natural Resources, Sydney.
Department of Infrastructure, Planning and Natural Resources, NSW (2005) Meeting the Challenge: NSW Salinity Strategy Premier's Annual Report 2003–04. NSW Department of Infrastructure, Planning and Natural Resources, viewed 12 May 2006, http://www.dlwc.nsw.gov.au/salinity/pdf/2003_2004_salinity_annual_report.pdf.
Department of Land and Water Conservation, NSW (2000) Taking on the Challenge: The NSW Salinity Strategy, Department of Infrastructure, Planning and Natural Resources, viewed 4 May 2006, http://www.dlwc.nsw.gov.au/salinity/government/govt-docs.htm.
Department of Land and Water Conservation, NSW (2002a) Soil Acidification Hazard Mapping (draft), produced for the 2003 NSW State of the Environment Report, Department of Land and Water Conservation, Parramatta.
Department of Land and Water Conservation, NSW (2002b) Surface Soil Acidity Mapping (draft), produced for the 2003 NSW State of the Environment Report, Department of Land and Water Conservation, Parramatta.
Department of Primary Industries, NSW (2005) Soil Management Following Drought, Agnote DPI 355, Third Edition, Department of Primary Industries, viewed 18 April 2006, http://www.agric.nsw.gov.au/reader/pasture-crops-recovery/dpi355.htm.
Department of Primary Industries, NSW (2006) Drought maps—areas of NSW suffering drought conditions, Department of Primary Industries, viewed 8 May 2006, http://www.agric.nsw.gov.au/reader/drt-area?picQuant=100.
DIPNR—see Department of Infrastructure, Planning and Natural Resources, NSW
DLWC—see Department of Land and Water Conservation, NSW
DPI—see Department of Primary Industries, NSW
Edwards, K and Zierholz, C (2001) Soil Formation and Erosion Rates, in PEV Charman and BW Murphy (eds) Soils: Their Properties and Management, 2nd Edition, pp 39–58, Oxford University Press, Oxford, cited in Lu, H, Prosser, IP, Monn, CJ, Gallant, JC, Priestley, G and Stevenson, JG (2003) Predicting sheetwash and rill erosion over the Australian continent, Australian Journal of Soil Research Vol. 41, 1037–1062, viewed 3 May 2006, http://palaeoworks.anu.edu.au/pubs/AustJSS03.pdf.
Hughes, AO and Prosser, IP (2003) Gully and Riverbank Erosion Mapping for the Murray-Darling Basin, Technical Report 3/03, March 2003, CSIRO Land and Water, Canberra, viewed 26 April 2006, http://www.clw.csiro.au/publications/technical2003/tr3-03.pdf.
Murray Catchment Management Board (2002) Integrated Catchment Management Plan for the Murray Catchment 2002: Murray Catchment Blueprint, NSW Department of Land and Water Conservation, viewed 2 June 2006, http://www.dlwc.nsw.gov.au/care/cmb/blueprints/pdf/murray.html.
Murrumbidgee Catchment Management Board (2003) Murrumbidgee Catchment Blueprint, NSW Department of Land and Water Conservation, Sydney, viewed 25 May 2006 http://www.dlwc.nsw.gov.au/care/cmb/blueprints/pdf/murrumbidgee_blueprint.pdf.
Prosser, IP, Williams, L (1998) The effect of wildfire on runoff and erosion in native Eucalyptus forest, Hydrological Processes, 12: 251–265, cited in Cooperative Research Centre for Catchment Hydrology (2006) Bushfires and Hydrology: Background—Other Physical Changes Due to Fire, Cooperative Research Centre for Catchment Hydrology, viewed 3 May 2006, http://www.catchment.crc.org.au/bushfire/background_otherchanges.html.
SCS—see Soil Conservation Service
Soil Conservation Service (1986) The Hidden Cost of Bushfires, Department of Land and Water Conservation, viewed 3 May 2006, http://www.dlwc.nsw.gov.au/care/soil/soil_pubs/pdfs/hidden_%20cost_bf.pdf.
Upjohn, B., Fenton, G. and Conyers, M. (2005) Soil Acidity and Liming Agfact AC.19 3rd Edition. NSW Department of Primary Industries, viewed 17 July 2006, http://www.agric.nsw.gov.au/reader/soil-acid/2991-soil-acidity-and-liming-.pdf
Wallbrink, PJ, Roddy, BP and Olley, JM (2002) A tracer budget quantifying soil redistribution on hillslopes after forest harvesting, Catena 47, 179–201, cited in Lu, H, Prosser, IP, Monn, CJ, Gallant, JC, Priestley, G and Stevenson, JG (2003) Predicting sheetwash and rill erosion over the Australian continent, Australian Journal of Soil Research Vol. 41, 1037–1062, viewed 3 May 2006, http://palaeoworks.anu.edu.au/pubs/AustJSS03.pdf.