Indicator: IW-26 Forested streamlength

Data

ERIN analysis of satellite data has derived the following information for all basins in the Intensive Landuse Zone. The following table summarises the analysis of these data.

Forested stream length and change by major divisions
Division	Total Km	Forested Length 1991	Forested Length 2004	Change by 1991	Change by 2004	Change between 1999 and 2004	Recent change as a proportion of total stream length
Total North-East Coast Drainage Division	353,763.00	202,309.40	201,361.20	151,453.60	152,401.80	-948.20	-0.27%
Total Western Plateau Drainage Division	1,411.00	197.00	179.00	1,214.00	1,232.00	-18.00	-1.28%
Total South-East Coast Drainage Division	236,038.05	140,114.40	141,642.35	95,923.65	94,395.70	1,527.95	0.65%
Total Tasmania Drainage Division	49,735.20	36,019.45	35,598.45	13,715.75	14,136.75	-421.00	-0.85%
Total Murray-Darling Drainage Division	457,027.30	129,181.00	132,323.55	327,846.30	324,703.75	3,142.55	0.69%
Total South Australian Gulf Drainage Division	23,807.55	4,942.75	5,176.05	18,864.80	18,631.50	233.30	0.98%
Total South-West Coast Drainage Division	96,494.35	28,093.55	28,494.45	68,400.80	67,999.90	400.90	0.42%
Total Indian Ocean Drainage Division	6,817.75	1,129.35	1,143.10	5,688.40	5,674.65	13.75	0.20%
Total Gulf of Carpentaria Drainage Division	46,796.85	23,309.15	23,092.30	23,487.70	23,704.55	-216.85	-0.46%
Total	1,271,891.05	565,296.05	569,010.45	706,595.00	702,880.60	3,714.40	0.29%

Source: Derived from AGO [Australian Greenhouse Office] 2006, Analysis of forest in Australia, unpublished data, Australian Greenhouse Office, Department of the Environment and Heritage. Source of data AGO Version 2, May 2006, NCAS, Department of the Environment and Heritage and the Australian Greenhouse Office, Canberra.

Forested streamlength in all Drainage Divisions of the ILZ

Detail in relation to each of these drainage divisions, and the data underlying this analysis, can be downloaded:

Forested streamlength (Excel - 235 KB)

Forest stream length by basin within the Intensive Landuse Zone, 2004

Source: Derived from Australian Greenhouse Office 2006, Analysis of forest in Australia, unpublished data.

Forested stream length change by basin within the Intensive Landuse Zone, 2004

Source: Derived from Australian Greenhouse Office 2006, Analysis of forest in Australia, unpublished data.

What the data mean

Forest is defined for AGO purposes as vegetation with at least 20% canopy cover and 2 metres tall.

In total, around 706,000 kilometres of forested streamlength, across all main drainage divisions, is estimated to have been lost between European settlement and 1991. (This assumes that the entire stream length in all divisions was vegetated at the time of European settlement). Nearly 4000 kilometres (less than 0.3% of total stream length) have been revegetated since 1991, mainly in the Murray-Darling Drainage Division, between 1991 and 2004.

Removal of riparian forest vegetation has been variable across drainage divisions. The banks of the Blackwood River and Albany Coast basins (South-west Coast Drainage Division, Western Australia), Goulburn River basin (Murray-Darling Drainage Division, Victoria) and Burnett River basin (southern part of North-East Coast Drainage Division, Queensland) have been heavily cleared (prior to 1991, the date of the earliest analysed satellite data), whereas several rivers in the same regions still have a significant forest cover.

All the rivers analysed in the northern part of the North-East Coast Drainage Division, Queensland, have forest vegetation along most of the bank. A few river basins, such as the Goulburn River, have increased the length of forest in recent years.

Overall, the most intact river basins are in the Tasmanian Drainage Division while the most clearing has occurred in the Murray-Darling Drainage Division. Forested stream length has changed very little since 1991, ie by then most clearing had already occurred and revegetation programs have not added much in comparison to the original forest extent.

Data Limitations

The data shows woody vegetation only. Native non-woody vegetation is not shown in these data. The analysis assumes that total stream length is the original extent of wooded streamlength, so that the differences between current wooded stream length and entire streamlength is the wooded streamlength lost since European settlement. This may not always be the case, as some streams may have always had, and still have, grassy or shrubby riparian vegetation, rather than woody vegetation, along part of their length.

To be included as wooded streamlength, the patches of woody vegetation have to be at least 50 metres in width on both sides of the river. In some cases, however, they may be much wider.

Data collection commenced in 1989. It is not known how much earlier than this date, the clearing of riparian vegetation occurred.

The analysis of the satellite data is of 1 pixel (25m) width along the streams and a different result is likely to be obtained if a wider analysis is taken.

The woody non-woody data is 'AGO Version July 2005'. This data was provided to ERIN by the AGO and was the best available information at the time. All subsequent analysis by ERIN assumes data are correct as received from the supplier. This is an 'Indicative Analysis Only' with a focus on monitoring trends through time and the comparison of the results between the IBRA regions.

Issues for which this is an indicator and why

Inland Waters — Habitat scale influences - Riparian vegetation

Although the indicator does not provide insight into the extent or condition of riparian vegetation, forested streamlength does provide a direct and measurable indication of how much of the length of Australian streams are protected by streamside vegetation, the streams, where it continues to be lost, where revegetation is occurring, and the rate at which the loss or revegetation is occurring.