Warringah Council’s Natural Area Survey has surveyed and mapped the native vegetation of the Warringah Local Government Area outside Ku-ring-gai Chase and Garigal National Parks. The NSW Department of Environment and Climate Change has mapped the vegetation within the national parks. The present report draws on this mapping to estimate the distribution of native vegetation types in the Warringah Local Government Area prior to European settlement, for comparison with their present distribution.
Maps have been produced and incorporated in Council’s geographic information system showing the distribution of the 11 native vegetation types in the Warringah Local Government Area in 1750 and 2000. A table has been compiled subdividing the 11 vegetation types into 37 vegetation communities and estimating the area of each community in 1750 and in 2000, with a further breakdown showing the reservation status of the remaining vegetation. Three additional communities have not been included in the analysis: two derived communities (not present in 1750), and a submerged aquatic community (not mapped).
Forty-one percent of the native vegetation of the Warringah Local Government Area has been lost since 1750, but the impact of clearing has been very uneven. Fifteen of the 37 vegetation communities have been cleared to less than 30% of their original area. The majority of these are communities that are more or less restricted to the vicinity of the coast (within 4 km), where very little native vegetation now remains. Away from the coast, the most reduced communities are those associated with shale lenses on ridges and plateaus in Hawkesbury Sandstone. The flat topography, absence of rock outcrops, and the more fertile soils, meant that these sites were selectively cleared for agricultural and later urban development in Warringah, in preference to the rocky, rugged, infertile sandstone areas.
Twenty-two of the 37 vegetation communities are poorly represented in reserves, with less than 15% of their estimated area in 1750 reserved in national parks or other reserves, or else with a reserved area of less than 5 ha. The 22 communities are:
• Bangalay Slopes Forest – 10% remains, 5% reserved (8 ha reserved)
• Silvertop Ash-Brown Stringybark Forest – 21% remains, 14% reserved (120 ha)
• Blackbutt-Turpentine Forest – 10% remains, 1% reserved (2 ha)
• Angophora-White Mahogany Forest – 100% remains (3 ha), none reserved
• Coastal Banksia-Eucalypt Scrub – 7% remains, 6% reserved (10 ha)
• Forest Oak Forest – 69% remains, almost all reserved, but only 2.5 ha
• Tall Open-forest/Closed-forest – 69% remains, all reserved, but only 4.5 ha
• Coastal Banksia-Teatree Scrub – 13% remains, almost all reserved (1.5 ha)
• Narrabeen Escarpment Scrub – 34% remains, 12% reserved (1.5 ha)
• Themeda Grassland – 13% remains, all reserved (0.7 ha)
• Lomandra Sedgeland – 23% remains, all reserved, but only 0.2 ha
• Sandstone Headland Heath – 13% remains, almost all reserved (7.5 ha)
• Heart-leaved Stringybark Mallee – 68 % remains, 7% reserved (0.3 ha)
• Estuarine Reedland – 16% remains, 10% reserved (5 ha)
• Estuarine Paperbark Scrub – 50% remains, all reserved, but only 2.5 ha
• Swamp Mahogany Forest – 16% remains, 12% reserved (4.5 ha)
• Bangalay Alluvial Forest – 16% remains, 13% reserved (41 ha)
• Palm Woodland – 16% remains, 9% reserved (8.5 ha)
• Water Fern Swamp – 16% remains, 13% reserved (5 ha)
• Paperbark Swamp – 16% remains, all reserved, but only 4 ha
• Coastal Freshwater Lagoon – 100 % remains, all reserved, but only 2 ha
• Coastal Dune Swamp – 1.5% remains, 1% reserved (0.5 ha)
The present report also reviews the issue of wildlife corridors, core habitats and landscape connectivity. Detailed definitions and criteria are developed and are used to map core habitats and wildlife corridors in the Warringah Local Government Area, including the national parks. The mapping is based on interpretation of high definition colour air photos taken in 2008, and has been incorporated in Warringah Council's geographic information system.