The Warriewood Wetlands

Introduction

The Warriewood Wetlands comprise approximately 30.5 hectares including Irrawong Reserve, and is zoned 7A, Environmental Protection. The remnant forest in the wetlands and Irrawong Reserve is part of the last significant stand of swamp mahogany forest in Sydney. It forms a corridor of important habitat linking the wetlands, the Ingleside escarpment and the coastal forests of Garigal and Ku-ring-gai Chase National Park. Palaeoecological studies indicate that the wetlands began as a coastal lagoon over 6000 years ago, which slowly infilled with sand and evolved into a freshwater habitat.

The Warriewood Wetlands was purchased by Pittwater Council in 1996, following an 18 year long battle by conservationists to retain the environmentally sensitive and regionally significant wetlands area which was privately owned. In the late 1970's, the then Wran Government agreed to let developers build a shopping centre on part of the site on the condition that Warringah Council would purchase the remainder of the site for retention as a natural area.

Dispute over what constituted a fair price for the area continued until 1996, when the matter was resolved in an out of court settlement which resulted in the purchase of the land by Pittwater Council for $4.5 million. The resolution of the issue means that this important environmental asset is now secured and conserved for the residents of Pittwater and for the benefit of future generations.

Flora and Fauna

The vegetation represented in the wetland area is quite diverse. There is a large area of swamp sclerophyll forest with a stand of Eucalyptus robusta (Swamp mahogany). Other dominant communities represented are Casuarina glauca (Swamp she-oak), Melaleuca ericifolia (Swamp scrub) and Phragmites australis (Common reed) with several other herbaceous and graminoid associations adjacent to the main water bodies.

The entire wetlands are important habitat for several bird and animal species. A large number of bird species have been recorded including several migratory birds covered by international treaties between the governments of Australia, Japan and China. Several frog and reptile species have been recorded, making the wetland one of the last refuges in the area for this type of fauna.

Conservation Significance

Warriewood Wetlands are of high conservation significance for the following reasons:

  • its status as virtually the last remnant of sandplain in the Sydney region.
  • its function in protecting the water quality of Narrabeen Lagoon as a filter and sink for sediments and nutrients.
  • its habitat value for flora and fauna, and the high level of biodiversity conferred by the variety of vegetation and habitats as well as by the wetland's large size.
  • its function as habitat for the endangered Black Bittern.
  • its function as habitat for the regionally significant plant species, Swamp Mahogany.

Pressures on the Wetlands

It is estimated that sections of various vegetation communities are heavily weed infested. The most invasive weed present is Ludwidgia (Ludwidgia peruviana), which has taken over the open water area and is colonising into the adjoining forest. In the swamp mahogany community, several invasive weeds are present including morning glory and lantana.

The weed infestation makes access difficult for arboreal fauna likely to use the forest area as habitat, although this situation has improved since the January 1994 fires and some restoration works. Open water channels are affected by the water weed, Salvinia molesta impeding the water bird habitat and water movement.

The major impacts affecting wetlands in the area are sediment and nutrient loading from a large catchment area with a history of intensive agricultural use, including market gardening and glasshouse production as well as urban development. The extent of sedimentation and the nutrient levels of that sediment is unknown, however weed infestation is an indicator of the presence of high nutrient concentration in the soil. The wetland itself acts as a natural sink and filtration system for the catchment and an important environmental buffer for the Narrabeen Lagoon.

Past landfilling of Warriewood wetlands has put additional stress on the remaining area by reducing the size of the functioning wetlands.