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The area and condition of native riparian vegetation by type. Ecosystem diversity and the integrity of fluvial geomorphic systems may be correlated with the extent and condition of native vegetation types within them. Different vegetation types are the products of different ecological and environmental conditions and, therefore, could reflect different habitats and components of ecosystems e.g. species composition and amount of available habitat. The extent and condition of native vegetation, by type, is the best available surrogate for the condition of terrestrial ecosystem diversity at this time. Native riparian vegetation has distinctive structural features and community attributes that could be used to evaluate its extent and condition. Riparian vegetation protects waterbodies from pollutants travelling overland in runoff, guards against excessive erosion, and is an important energy source (through litterfall) for aquatic ecosystems. Retention or loss of riparian vegetation has a major impact on physical (and biological) processes in watercourses; consequently changes in riparian vegetation, together with catchment vegetation cover changes, are important pervasive influences on aquatic ecosystem and fluvial and karst system integrity.
Assessment of Tasmania's riparian vegetation, December 2001 This assessment was conducted as part of the National Land and Water Resources Audit. It was conducted through a workshop process that combined expert opinion and the presentation of independent analyses. Bioregion Condition Trend Threatening processes (see list below) Ben Lomond Fair Declining 1,2,3,4,5,6,7,10,11 Central Highlands Good Static 1,2,3,4,5,6,10,11,12 Flinders Degraded Declining 1,2,3,4,5,6,9,10,11,13 King Good Declining 1,2,3,4,6,9,10,11,12,14,15,16 Northern Midlands Degraded Declining 1,2,3,4,5,6, 9,10,11,12,15 Northern Slopes Degraded Declining 1,2,3,4,5,6,9,10,11,12,17 South East Fair Declining 1,2,3,4,5,6,7,8,9,10,11,12,14,15,18 Southern Ranges Good Static 1,2,3,4,5,6,9,10,11,12,14 West Good Static 1,2,3,4,5,6,7,8,9,10,11,19 NLWRA Threatening Processes Other Threatening Processes Source: Adapted from Dunn 2002 In the 460 native riparian sites investigated by Daley 2003, 857 native vascular taxa were recorded in the riparian zone as well as 89 exotic species. In Tasmania, 77 vascular plant species are characterized as riparian species. Of these, only two are considered to be confined to the riparian zone (Alex Buchanan, Tasmanian Herbarium, pers. comm.). Many endemic, rare, vulnerable and endangered plants are also known to occur mainly in the riparian zone. It is estimated from analysis of The LIST hydrological data that Tasmania has approximately 39,000km of major watercourses. In 1993, there was an estimated 1,500 km2 of significantly degraded riparian zones in agricultural areas of Tasmania (Land and Water Resources in Geraghty and Ratcliffe 1993). In 1998, data on river disturbance related to human intervention was collected as part of the assessment for the Regional Forest Agreement. The unpublished data from the project shows that moderate to substantial disturbance was evident along approximately 20,855 km of major streams and watercourses (River Disturbance Index, Wild Rivers Project, 1998). If the Forest Practices Code maximum riparian buffer of 40 m for each bank is used to evaluate area of moderately to substantially disturbed riparian zone (Forest Practices Board 2000), then a conservative estimate of 1,668 km2 of a possible 3,120 km2 of the riparian vegetation along major water courses in Tasmania was categorised as moderately to substantially disturbed in 1998. Estimated area of riparian zone disturbance in 1998 Wild rivers
Length of stream
Area of stream (km2)
% No disturbance value 35 - No disturbance 6,930 554 18 Minor disturbance 11,370 910 29 Moderate disturbance 18,055 1,444 46 Substantial disturbance 2,800 224 7 Disturbances to minor streams and headwaters are not taken into account in the calculations in this table Source: Adapted from RDI data derived from Wild Rivers Project, 1998 The condition of Tasmania's riparian vegetation varies around the State. Evaluation of riparian vegetation condition is based on extent, intensity and number of disturbances, and recovery potential for each bioregion. (Dunn 2002 and Daley 2003). All bioregions have stretches of remnant native riparian vegetation in excellent condition. These stretches are usually located in areas that are remote or in conservation areas or reserves, but are also found on private land. The size, extent and location of reserves are not equally spread across the State. Maintenance and management of riparian areas within reserves also varies across the State. In the absence of historic data on native riparian vegetation, an evaluation of trend is based on whether the sum of the cumulative pressures and activities within a bioregion are continuing or not. For example, if there are regional plans to continue or increase in-stream dams, agricultural productivity and native forest clearing, then the trend for the bioregion is evaluated as 'declining.' The 'decline' in condition of riparian vegetation was rated as a slower trend, in contrast with a 'rapid decline' (<10 years) time-frame. The assessment of a slower rate of decline offers an opportunity for intervention to reduce the threatening processes impacting on the riparian zone, stabilisation and restoration (Dunn 2002). Adapted from core biodiversity indicators BD7 and IW7 (ANZECC 2000) using Dunn 2002 and Daley 2003. |
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