Fringing (or riparian) vegetation is an integral part of a riverine ecosystem and includes the terrestrial and emergent vegetation that borders and is influenced by the waterway. Fringing vegetation provides food and shelter for many bird species and other small animals.
A dense network of roots enables fringing vegetation to stabilise riverbanks and protect them against erosion from boat wash, river flow and surface water run-off.
Fringing vegetation helps to reduce nutrients and sediment entering waterways by slowing the rate of overland runoff, enabling sediments to settle and nutrients to be trapped and used on land.
Overstorey species provide shade to waterways and reduce water temperature. They also drop leaves, bark and insects into the waterway, providing food to aquatic invertebrates and fish. Woody debris in the form of fallen trees and branches provide structure, food and habitat along the shoreline. Woody debris provides important shelter for fish and helps deflect erosive forces away from the banks.
Riparian vegetation is reduced or removed from a foreshore through disturbance including:
Grasses and weeds often replace native fringing vegetation, and often have only shallow roots making the banks more vulnerable to the hydraulic forces that cause erosion. Bank undercutting and slumping can occur which contribute to increased sedimentation of waterways. More rapid runoff increases nutrients and sediment entering the waterways.
In-stream light availability and temperature increase without overstorey shading and, where nutrients are available, encourages the growth of submerged aquatic plants, periphyton (the collection of organisms such as algae and bacteria that live on the surface of submerged plants and other underwater objects) and filamentous algae. Where plant growth is excessive it can increase the amount of decomposing organic matter instream, reducing oxygen levels. In-stream plant growth also helps to trap sediments moving downstream, promoting channel infilling and smothering habitat.
Reduction in terrestrial insects, woody debris and leaf litter in-stream and increased growth of submerged plants, periphyton and filamentous algae changes habitat and food for fish and invertebrate communities. This reduces diversity, with degraded waterways often dominated by fewer species.
It is an offence under the Swan and Canning Rivers Management Regulations 2007 to damage vegetation in the Swan Canning Riverpark or Development Control Area (DCA). Parks and Wildlife encourages appropriate planning and development in the DCA and has a range of planning control measures and processes to facilitate and evaluate development applications around the rivers, depending on where the development is located.
Occasionally foreshore vegetation is damaged by people who did not realise they needed a permit to carry out maintenance. However, in some cases, trees have been systematically poisoned, have had their limbs removed or are cut down. Tying boats or dinghies damages foreshore vegetation and is an offence.
Parks and Wildlife regularly receives complaints from the public about deliberate foreshore vegetation damage in the Riverpark. These are thoroughly investigated in consultation with land managers.
Offenders may face penalties of up to $5000 under the Swan and Canning Rivers Management Regulations 2007.
Signs are installed at some tree damage sites to educate the community about the value of vegetation and encourage reporting of tree damage.
Generally new trees are planted and damaged trees left standing (as long as it is safe to do so) while the new tree grows.
The public are encouraged to report any acts of environmental vandalism to Parks and Wildlife on 9278 0900, or after hours on 0419 192 845.