Ecological impacts of recreational vehicle use on saltmarshes of the Georges River, Sydney

The unauthorised use of recreational vehicles (trail bikes, BMX, 4WDs, mountain bikes) is a major threat to many saltmarsh communities of the Georges River, Sydney. Analysis of historical aerial photographs was undertaken to quantify the saltmarsh areas damaged by vehicle use and a field study conducted to assess the associated ecological impacts. The field study involved a comparison of vegetation, soil and invertebrate fauna parameters between undisturbed, low and high track density areas of four communities dominated by the low-growing chenopod Sarcocornia quinqueflora and two communities dominated by the taller rush Juncus kraussii.

Aerial photo analysis showed that over 21000m² of saltmarsh has been directly impacted by vehicle use along the Georges River, with observations of vehicle use suggesting a continuing increase to this area. The field study showed that vegetation cover, soil compaction, soil moisture, and mollusc and crab distributions were all adversely affected by vehicle use. In Sarcocornia communities the impacts were most severe in areas of high track density, though single track areas also showed significant effects. Juncus communities generally showed less damage, due in part to morphological characteristics of the dominant plant species. In both community types vehicle ruts and excavations were prone to waterlogging, could alter vegetation composition and facilitate the breeding of mosquitoes and spread of mangroves. Recommendations are made for the control of vehicle use and restoration of damaged saltmarshes