State of the Environment Report 2007
Fringing vegetation is the vegetation that grows alongside a waterway or wetland. This issue relates to waterways, as wetland associated vegetation is covered elsewhere (see 'Loss or degradation of wetlands'). Fringing vegetation has adapted to inundation or waterlogged conditions, has an important role in the ecology of waterways, and provides a vegetated linkage between aquatic and terrestrial ecosystems. It provides habitat for both aquatic and terrestrial fauna and provides wildlife corridors, so is essential to biodiversity conservation. Overhanging vegetation regulates light availability and temperature in the water body, preventing weed growth and algal blooms. Fringing vegetation also intercepts and filters nutrients, pollutants and sediments leaving the catchment and helps to stabilise embankments from erosion. Instream vegetation consists of aquatic plants within a waterway or wetland. It helps to stabilise streambeds, recycle nutrients in the water column and serves as food and habitat for aquatic organisms.
Historically there has been little value placed on retention of fringing and instream vegetation. In many populated areas, fringing vegetation along estuaries, rivers and wetlands has been removed to provide water views for residential development and to enhance land values. In some agricultural areas, fringing vegetation has been removed to enable farming of productive floodplain soils. Similarly, instream vegetation has been removed during dredging activities to allow boat navigation. In some waterways, nutrient and sediment pollution has contributed to significant degradation of seagrass communities.
Information about changes in fringing vegetation remains extremely limited and has not been comprehensively updated since the 1998 State of the Environment Report. While foreshore surveys of fringing vegetation are occasionally undertaken for waterways in the South West, the information has not been centrally collated. In contrast, foreshore assessments in the rangelands is extremely difficult given the difficult terrain, vast size of some catchments and limited accessibility. Aerial surveys and satellite imagery are sometimes used for these reasons.
Satellite imagery shows fringing vegetation of waterways is still being lost or degraded throughout the South West. Net declines in fringing vegetation are apparent in many coastal catchments between Bunbury and Geraldton, due to land development, drought and rural activities (Figure IW4.1). Declines in fringing vegetation for the Blackwood and Moore rivers and southern reaches of the Avon River are likely to be due to the effects of salinisation. Net gains in fringing vegetation are apparent for some waterways near Perth, Mandurah, Collie and Albany, and may be due to increased weed abundance or revegetation rehabilitation and restoration efforts. Further ground truthing and frequent foreshore assessments are required to verify these findings.
Foreshore condition of Mid West rivers are generally poor. For example, 50% of the sites on the Greenough, Chapman and Hutt rivers have lost more than half their native vegetation, with minimal understorey and a dominant weed presence. Specifically, about 34% of foreshore on the Hutt River was in a good or very good condition (Department of Environment, 2005b). Foreshore assessments have also shown that tributaries of the lower Avon River, such as the Brockman, Mortlock, Toodyay and Mackie rivers are in a generally degraded condition due to previous and current farming activities.
Surveys on the Swan-Canning Estuary and its major tributaries indicate minimal retention of native vegetation and a significant weed presence, with the exception of the upper reaches of the Helena and Canning rivers which remain largely forested. Most of the estuary foreshore has been found to have more than 70% weed cover, indicating a substantial shift of fringing vegetation from its natural state (Swan River Trust, 2006).
Surveys of river foreshores in the Oyster Harbour catchment near Albany, found 81% to be in a degraded condition that were erosion prone or weed infested, with about 55% of foreshores fenced (Water and Rivers Commission, 1997a). In the upper reaches of the Kent River catchment, 92% of surveyed foreshore area was in a similar degraded condition, with about 67% of foreshores fenced (Kent River LCDC and Water and Rivers Commission, 1998).
![Figure IW4.1: Net loss or gain of vegetation within 50 metres of waterways in South West catchments, 1996–2004. [Data source: Department of Land Information – Land Monitor [ver. 2004]; Analysis: EPA; Presentation: EPA.]](/site/files/images/Figure-IW4.1_Large.jpg)
Current monitoring of instream vegetation is limited to a few South West estuaries. Seagrass and macroalgal species and distribution have been periodically well researched in the Swan-Canning and Peel-Harvey estuaries, Princess Royal and Oyster harbours, and Wilson and Leschenault inlets (Brearley, 2005). Instream vegetation in rivers and wetlands is generally not monitored and it is therefore not possible to report on condition or changes over time. For estuaries it is generally understood that once seagrasses have been lost or disturbed they may never recover (Clarke & Kirkman, 1989; Kirkman & Kuo, 1990). Large declines in seagrass in the 1970s, due to massive increases in macroalgae, were documented in the Peel-Harvey estuarine system near Mandurah (McComb & Lukatelich, 1995). However, construction of the Dawesville Channel has significantly altered macroalgal distribution and diversity, and has also contributed to the loss of some fringing vegetation with increasing tides and salinity in the estuary (Brearley, 2005).
In Princess Royal Harbour and Oyster Harbour near Albany, 90% and 80% of seagrass was lost, respectively, between the early 1960s and the late 1980s (Hillman et al., 1990; Water and Rivers Commission, 1997b). However significant recovery was noted in the mid-1990s, coinciding with a series of dry years with reduced catchment runoff and decreasing macroalgae (Bastyan et al., 1996). With significant restoration and rehabilitation efforts being undertaken in Oyster Harbour, there is now emerging evidence that seagrass meadows (Posidonia sp.) are recovering (G Bastyan, pers. comm.). Enhanced seagrass (Ruppia sp.) growth was also observed in nearby Wilson Inlet during the 1980s but is now declining there due to increasing algal blooms.
Many WA settlements were established in lowland valley areas adjacent to waterways to allow easier transportation, access to water and because of the better agricultural productivity on floodplains. This resulted in extensive removal of fringing vegetation in some areas, such as the upper Swan and lower Avon rivers. Damage to fringing vegetation is still occurring as a result of residential developmental and the cultural appeal of owning a waterfront property with water views. This is particularly evident for land adjacent to estuaries and major river systems across the South West. Pressures such as clearing, salinisation, over grazing, erosion, Phytophthora dieback, altered fire regimes, and feral and weed invasion are also degrading remaining fringing vegetation. Altered water regimes can seriously degrade fringing vegetation by causing flooding or reducing water availability. Increasing levels of acid, sediment and other pollutants in waterways can also contribute to loss of fringing vegetation.
In agricultural areas, acute loss of fringing vegetation continues to occur where stock has easy access to waterways and wetlands. Recent surveys undertaken in the South West agricultural region indicate that 45-50% of farmers protect river creek frontages from grazing animals (Department of Agriculture, 2006). Grazing is also a problem for waterways and wetlands in the rangelands, where stock depend on access to water in an otherwise dry landscape. The topography of the land and extent of pastoral livestock grazing areas means that it is often impractical to fence large portions of waterways and wetlands. Only 33% of pastoralists indicated that they protect river or creek frontages from grazing animals (Department of Agriculture, 2006).
The major pressure associated with loss of instream vegetation is dredging to aid navigation for recreational boating, commercial operations or tourism charters. Estuaries or major river systems with port, harbour, marina or boating facilities undertake occasional dredging of channels to prevent them filling with sediment. Sometimes removal of seagrass occurs but can be minimised with adequate management practices. Many WA estuaries including the Swan, Peel Inlet, Harvey (Dawesville), Oyster Harbour, Murchison River and Leschenault estuaries are dredged to maintain navigation channels. Sedimentation, eutrophication and salinisation can also radically affect the extent and density of instream vegetation but unfortunately there is little or no ongoing monitoring to assess these changes.
Vegetation clearing regulations: Amendments were made in 2003 to the Environmental Protection Act 1986 to provide regulations that protect native vegetation while allowing for approved clearing activities. The regulations extend to protection of instream and fringing vegetation of wetlands and waterways.
Planning policy: A Water Resources Statement of Planning Policy (Western Australian Planning Commission, 2006a) has been prepared by the Western Australian Planning Commission to assist with the management and protection of wetlands (and other waterways) in the land use planning system. An accompanying draft Guideline for the Determination of Wetland Buffer Requirements (Western Australian Planning Commission, 2005) has also been released to provide advice on minimising planning and development impacts to wetlands. A new State Planning Policy (Western Australian Planning Commission, 2006b) has been developed specifically for the Swan-Canning river system to ensure that new development does not compromise the health, amenity and landscape values of the rivers.
River and wetland restoration manuals: A river restoration manual has been developed to assist with restoration and long-term management of waterways (Water and Rivers Commission, 2002). A wetland restoration manual is in development by the Department of Environment and Conservation. These manuals provide information on how waterways and wetlands function, the causes and effects of degrading processes, and planning, restoration and management techniques.
Natural Heritage Trust/National Action Plan for Salinity and Water Quality (NHT/NAP) programs: All regional Natural Resource Management groups in the South West have recognised loss of fringing vegetation as a major threat to inland waters. Many other regional groups will address this as part of estuary, waterway and wetland management. The regional groups are developing projects for management of affected waterways and protection of valued natural assets at risk.
Foreshore policy and assessment: In 2001 the Water and Rivers Commission approved a policy that provides a consistent methodology for assessment and determination of waterway foreshore and buffer areas. The foreshore assessment technique for waterways in the South West does not require expert knowledge and covers bank stability, foreshore vegetation condition, stream cover and habitat diversity.
Riverbank Program: is administered by the Swan River Trust to provide project funding for the rehabilitation and protection of foreshores along the Swan and Canning rivers. A baseline study has recently been undertaken, in partnership with the Swan Catchment Council using Natural Heritage Trust assistance, which assessed fringing vegetation condition along 61 km of foreshore. A comprehensive assessment of shoreline type, vegetation and weed cover was undertaken along the Swan Canning Estuary.
Streamlining: Streamlining of agricultural drains consists of fencing waterways and drains to prevent livestock access, and revegetating the fringes using native species. Incentives can be offered to encourage landholders to fence to exclude stock from drains and to revegetate where possible.
Fringing vegetation research: The Tropical Savannas Cooperative Research Centre is conducting a research project on fringing vegetation across Northern Australia, including in the Kimberley. The project aims to define fringing vegetation health, develop practical methods to assess foreshore condition, generate better understanding of threatening processes and evaluate techniques to manage those threats.
Loss of fringing and instream vegetation is often a contentious issue. In some urban riverside areas, fringing vegetation has been illegally poisoned to allow for improved water views. In some rural and sparsely populated areas the loss of fringing vegetation goes largely unnoticed until obvious downstream impacts on biodiversity or water quality begin to occur. There is a need to increase community awareness of the value of fringing and instream vegetation and its importance for maintaining healthy waterways and wetlands. Failure to do this will result in loss of ecological functionality of inland waters (including loss of habitat and food sources for fish and other native animals), and may impact on tourism and recreational and commercial fishing. Loss of fringing vegetation allows more light to reach the water body, enhancing weed and algal growth. Inland waters without fringing and instream vegetation will also become more susceptible to the effects of erosion and sedimentation, causing potential for flooding and navigation problems.
4.14 Establish an agreed baseline of the condition of fringing and instream vegetation.
4.15 Implement the Water Resource Statement of Planning Policy and finalise the draft Guideline for the Determination of Wetland Buffer Requirements.
4.16 Develop and implement a package of education, assistance and incentives for fencing and rehabilitation of waterways and wetlands on private lands.