SHRUBLANDS AND HEATHLANDS

OF THE WET TROPICS BIOREGION METCALFE © DAN Shrublands and heathlands (vegetation codes 67a-67k)

Shrublands and heathlands encompass a diverse range Aeolian dune fields are very uncommon in the Wet Tropics, of floristic associations. The extent and distribution of being limited to a few occurrences on the Cairns, many of these is highly restricted due to specific Helensvale and Hinchinbrook Island map sheets. Although environmental requirements. Sclerophyll shrubs coastal heath communities are more typical of the Cape dominate the formation, although rainforest tree species York Peninsular Bioregion, relatively extensive areas are may occasionally be present depending upon the found on both the Cairns and Helensvale map sheets. Field prevailing environmental conditions. Many of the observation suggests that the aeolian process was much constituent species are shrubland specialists, although a more active in the past but over time a gradual reduction in significant number are common canopy constituents of sand deposition has enabled the incremental stabilisation well developed rainforest and woodland communities. A of the dune fields by myrtaceous shrubs. large number of shrubland communities have also been For example, on the Cairns map sheet dune fields may be incorporated as alliances in other formations based upon occupied by a Thryptomene oligandra heathland (67c) while their floristic association. the Archer Point (Helensvale map sheet) dune field has In this classification a shrub is a woody less than 8 been colonised by a more diverse mix of shrubs metres tall, frequently with multiple stems arising at or which include: lysicephala, Asteromyrtus near the base (after Specht 1970), while the term heath angustifolia, Thryptomene oligandra, Acacia crassicarpa, refers to shrubland communities where crown cover Jacksonia thesioides and Leucopogon yorkensis (67k). In a exceeds 80%. bioregional context, these shrublands are unique. The rugged, elevated topography of Hinchinbrook Island hosts a range of shrubland communities. Type 67a is an Younger prograding dune systems in the Department of unusual shrubland association, occurring on Mount Defence training area at Cowley Beach host a unique Straloch at altitudes above 600m at the southern end of shrubland complex (67j) controlled largely by seasonal Hinchinbrook Island. The community, characterised by fluctuations in the ground water table. The landscape is Acacia celsa, Podocarpus grayae and Callitris endlicheri, characterised by regularly alternating dune ridges and blankets extensive areas of exposed hillslope on highly perennially wet swales, with the dune ridges rarely infertile acid volcanic detritus. Notophyll rainforest elevated more than a metre above the high point of the occupies adjacent sheltered locations where it attenuates swale. The suppressed topography has not facilitated the along incised gullies and crevasses. Acacia flavescens development of soil that is sufficiently drained at any point dominated shrubland (67b) is prominent on rocky in the landscape to allow development of anything but a headlands where it merges upslope with areas of depauperate shrubland dominated by viridiflora. Allocasuarina littoralis dominated shrubland (67f), which is habitat for the endemic plagiocarpa. Unlike association 67a, this community is directly influenced by Lophostemon is a prominent in a number of fire which is an important habitat regulator and controlling shrubland associations. Lophostemon confertus dominated factor. Observations suggest that hot fires destroy Banksia shrublands (67h) has an extensive distribution on Walsh's plagiocarpa shrubs and that their subsequent regeneration Pyramid (Gordonvale map sheet) and is also a significant is suppressed by the aggressive invasion of Allocasuarina component of the broader rock pavement complex spp. formation. The association consistently occupies the more favourable sites in sheltered enclaves amongst the broader rock pavement formation. The structural and Allocasuarina spp. are particularly well-adapted at floristic uniformity, coupled with the areal extent of these colonising harsh environments (67e). In a very wet area to shrublands warrants their recognition as a separate entity. the south of Innisfail there is a lens of deeply weathered Lophostemon suaveolens is a common shrub species of ultramafic rock forming a low linear ridgeline which has rock pavement complexes, often forming near pure stands. been colonised by an Allocasuarina littoralis dominated These shrublands have, however, been mapped as a shrubland. It is apparent that there is some degree of soil component of a broader rock pavement complex formation toxicity associated with the unusual geology which severely (example 66c) due to their limited areal extent and their limits most vegetation development. It is very unusual to inconsistent expression across the broader landscape. find such a depauperate sclerophyll community in a high Association 67i does, however, recognise the floristic rainfall belt, on what appears to be a soil of reasonable dominance of Lophostemon suaveolens in a mixed tall open structure and depth, in an area that has not been subject shrubland community in the Windin Falls area (Bartle to any severe disturbance event. Frere map sheet). This association is delineated on © DAN METCALFE with as a occupied byvinethicket communities. Althoughclassified depressions onthealluvialsurface andtheseareas are (beach ridges).Rockrubble moundshave beenexposed in occupy anumberofextremely narrow stranded shorelines the protection provided bytheboulder mounds. incursions withthegroves ofvinethicket survivingdueto most likely beeninfluenced inpartbyregular fire complexity ofthecommunity shouldberecognised. Ithas scattered widely separated groves ofvinethickets, grasslands, Curacoa Island(Palm IslandGroup). Itsstructure isoneof is confined to anextensive flatonthenorth-west sideof Association 67gisanunusualshrublandcommunity which favourable environmental conditions. dominant formation isfound down-slope inmore whereas themore extensive neighbouringsyncarpia ridgelines withextreme drainage andskeletal soils, Area protected bioregion Current extent inthe Vegetation alliances Facts andfigures alluvial outwash,groves of Although thelandform iscomposed predominantly of landform. and thelackofsubstrate homogeneityintheoccupied complex can beattributed to boththerecent nature of, shrublands andwoodlands.Thisunusualvegetation Corymbia tessellaris Corymbia Corymbia tessellaris Corymbia equisetifolia Casuarina Melaleuca viridiflora Melaleuca shrublands suaveolens Lophostemon shrublands confertus Lophostemon tessellaris Corymbia shrublands littoralis Allocasuarina shrublands lysicephala Asteromyrtus flavescens Acacia celsa Acacia 7,817ha (80%) 9,783ha dominant alliance, thestructural Casuarina equisetifolia Casuarina and shrubland interspersed shrublands Acacia crassicarpa Acacia shrublands shrublands shrublands tend to reduction of floristic diversity inthesecommunities. managed fire regimes are likely to result insevere thickening mayoccur intheabsence offire. Poorly species mayoccur after ahotfire event, oramore gradual by heathland alliances. Theexception isthosecharacterised structural changeinthemajorityofshrublandand Edaphic controls limitthedegree andrate offloristic or Impacts andchanges drained orskeletal soiltypes. important controlling factors are highly infertile, poorly Although theformation occurs onarange ofgeologies, the Hinchinbrook Islandandadjacent mainlandareas. shrubland areas are associated withthesteep terrain of escarpment orcoastal plain.Themost extensive This formation islargely confined to areas onthecoastal Geography Appropriate fire regimes important to maintenance of • Management considerations Fitzroy IslandNP,Paluma RangeNP,Tully Gorge NP. Extensive areas conserved ontheHinchinbrook IslandNP, Tenure Loss offloristic diversity associated withinappropriate • Threatening processes Habitat oftheendemic • Form extensive wilderness areas onHinchinbrook Island • Key values floristic diversity in fire regimes. NP withconsiderable scenic value Allocasuarina littoralis Allocasuarina Allocasuarina littoralis Allocasuarina where prolific regeneration ofthe Banksia plagiocarpa Banksia wettropics.gov.au alliances. .