Open woodlands are scattered across the higher levels of Hawkesbury Sandstone uplands. In exposed settings, trees are generally smaller, more straggly and spaced more widely, grading or changing abruptly into patches of tall shrubland, heathland or swamp. But tree size increases on slopes with some mighty Sydney red gums among clefts and boulders.
Such woodlands are eucalypt-dominant, notably with Sydney peppermint Eucalyptus piperita, Sydney red gum Angophora costata, silvertop ash E. sieberi, scribbly gums E. haemastoma and E. racemosa and red bloodwood Corymbia gummifera, the latter accompanied in the west of the GeoRegion by yellow bloodwood C. eximia
Photo: Open forest in Ku-ring-gai Chase viewed from Kalkari visitors centre. The flowering trees are Sydney red gums Angophora costata.
Dwarf apple Angophora hispida and black sheoak Allocasuarina littoralis are widespread. Sandstone stringybark Eucalyptus oblonga grows on high points overlain ultimately by Mittagong Formation as is Silvertop ash. Two species, Angophora crassifolia and yellow-top mallee ash Eucalyptus luehmanniana, are limited in distribution, confined to upland reserves towards the coast and listed vulnerable, the GeoRegion being one of their refuges. Large-fruited red mahogany E. scias subsp. scias is strongly local being confined to West Head in the GeoRegion while broad-leaved white mahogany E. umbra is common in the area but is at the southern limits of its range. Camfield’s stringybark E. Camfieldii , sometimes called heart-leaved stringybark from its juvenile leaves, is uncommon and listed vulnerable but occurs at several localities in Ku-ring-gai Chase National Park.
Photo: Sydney red gums can grow large and sturdy in extremely rocky sites, like here at Resolute lookout in Ku-ring-gai Chase.
Hawkesbury Sandstone country is dissected by numerous steep sided valleys, and forests can thrive in the deeper more sheltered ones, though much depends on aspect. Sandstone valleys in the GeoRegion carry tall blackbutts Eucalyptus pilularis, turpentines Syncarpia glomulifera, Sydney red gums Angophora costata, forest oaks Allocasuarina torulosa and scattered Christmas bushes Ceratopetalum gummiferum. Closer to the coast, like in the valley of Middle Harbour Creek, ribbons of forest in the valleys are created by tall Sydney red gums accompanied by Sydney peppermints and broad-leaved white mahoganies Eucalyptus umbra. Such moist valley settings offer protection from hot, dry north-westerlies and fires.
Tall eucalypt forests tend to have open crowns stimulating a rich and diverse sound flora and even vine-laced rainforest understorey in sheltered, high rainfall settings. Shrubs include beard-heaths especially Leucopogon lanceolatus and L. juniperinus; pea flowers such as Platylobium formosum, Phyllota grandiflora and Pultenaea flexilis, Fraser’s boronia Boronia fraseri and cream-flowered toothed phebalium Leionema dentatum. Orchids include pixie caps Acianthus fornicatus, hyacinth Dipodium species, Cryptostylis and greenhood Pterostylis species. Then there are guinea flowers like Hibbertia dentata and H. bracteata; climbers such as Clematis aristata, wonga vine Pandorea pandorana and five-leaf water vine Cissus hypoglauca; ferns such as rainbow fern Calochlaena dubia and gristle fern Blechnum cartilagineum.
Photo: Yellow bloodwood Corymbia eximia, Muogamarra Nature Reserve.
Riparian and Gallery Rainforests
Streams descend from sandstone plateaus by distinct trains of waterfalls and rapids (called knickpoints and knickzones) marking stages of their progressive upstream-deepening erosion cycles. These are commonly stalled and focused by thick, massive sandstone beds creating waterfalls, and the GeoRegion hosts some spectacular ones. Seepages from shady valley sides support a cooler environment that’s enhanced by water trickling from small tributary valleys overhung with broad-leaved shrubs and trees and carpeted with ferns.
Photo: Rare and threatened, Camfield’s stringybark Eucalyptus camfieldii, near Elvina trailhead, Ku-ring-gai Chase.
Rapid, rocky, bubbling streams are almost devoid of alluvium and so the plants that thrive near them are ones whose roots can worm among the rocks and boulders accessing nutrients percolated in or washed in by flooding. Principal of these is water gum Tristaniopsis laurina which is largely restricted to rocky banks and creek beds and it is stoutly resistant to flooding. You may also encounter its shrubby and more brightly flowered cousin Tristania neriifolia sprouting from rock crevices. Coachwoods Ceratopetalum apetalum, grey myrtles Backhousia myrtifolia and black wattles Callicoma serratifolia are common gallery rainforest trees or large shrubs of small sandstone valleys and gorges, to which one may add white cherry Schizomeria ovata, sweet pittosporum Pittosporum undulatum, lillypilly Acmena smithii and sandpaper fig Ficus coronata. Tall shrubs like scrub beefwood Stenocarpus salignus, satinwood Nematolepis squamea subsp. squamea and river lomatia Lomatia myricoides may be present.
Five-leaf water vine Cissus hypoglauca thrives in such settings.
Photo: A characteristic tree of rocky Hawkesbury Sandstone creek lines, water gum Tristaniopsis laurina is flowering here firmly rooted in the rocky bed of Middle Harbour Creek, Garigal National Park.
The valleys and gorges of Hawkesbury Sandstone country converge into larger valleys which can be more than 150 metres deep, becoming tidal inlets downstream. Seawards, an estuary shoreline may shelter littoral rainforest. Such shorelines are of course at sea level and will benefit from more reliable high humidity and greater rainfall regularity.
The floras of shoreline cliffs, notches and enclaves can be surprisingly rich especially on south-facing shorelines, and may feature species normally found in sheltered inland settings and on richer soils. Rough-barked apple Angophora floribunda thrives in such settings. Figs are usually represented, especially Port Jackson Ficus rubiginosa. Additional species appear where merging with saltwater, notably swamp oak Casuarina glauca and one or both local species of mangrove, grey Avicennia marina and river Aegiceras corniculatum and its groundcover relative, creeping brookweed Samolus repens. And where the shoreline broadens to include mudbanks there may be samphire Sarcocornia quinqueflora.
Photo: Riparian rainforest in the sandstone valley of Lane Cove River.
