This is a diverse formation whose major environmental

controlling factors are skeletal soils and exposure. The

formation encompasses a range of structural and

floristic types more typical of other formations; however

it was not possible to map these individual components

due to both the scale of the variation and its complexity.

Geography provides a dominant control on its expression

with variation occurring in response to position in the

landscape, position in the bioregion (climate) and, to a

lesser extent, geology. The formation comprises two

alliances that can be distinguished by landscape position.

The coastal headland complexes are characterised byexposure to the prevailing trade winds, salt spray andsteep slopes which rapidly shed surface water preventingthe formation of anything but the most skeletal rocky soils.Association 66a is a variable heathland/shrublandcommunity that has a number of scattered and disjunctoccurrences on coastal headlands and islands throughoutthe bioregion. The association ranges from a low openshrubland to shrubland with species from the Myrtaceaeand Mimosaceae families dominating the shrub layers.Ground covers are typically sparse although the grassThemeda triandra is always present mixed with a variableassemblage of ephemeral herbs, low shrubs, grasses andlianes. With increasing soil development or greaterprotection from exposure, low woodlands to open forestsstructural types are possible (66b) and is much moreextensive than 66a as it can occur in all climatic zones. It istypically a low woodland dominated by Lophostemonsuaveolens, Corymbia tessellaris and Acacia spp. andgenerally merges upslope with much better developedeucalypt woodland or rainforest associations.

Rock pavement complexes occur throughout the bioregionand across all climatic zones. Typically their majoroccurrences are associated with rocky coastal ranges indry to wet regions, and in the drier western parts of thebioregion. Association 66c is the most extensively mappedand widely dispersed community, however its floristiccomposition and structural expression is both poorlyconstrained and highly variable. The association mayencompass elements of fernland, sclerophyll heath,woodland, and low vine thicket in various closelyinterspersed combinations. The association is classifiedaccording to the prevailing ecological controls of skeletalsoil and exposure rather than floristic or structuralexpression. Similarly, Association 66e is separated fromsurrounding woodland communities on the basis of ashallowing of the soil profile, manifest as a reduction inwoodland stature and canopy cover. The floristic

composition of Association 66e is similarly variable, mostclosely aligned to the adjacent woodland types from whichit was derived.

A number of communities within this alliance provide amore structurally and floristically consistent expression,although these are generally restricted to particulargeographic locations. Association 66f is confined to rocky,acid volcanic pavements on the dry western and southernmargins of the bioregion where Acacia leptostachya formsextensive areas of low shrubland, interspersed with areasof bare pavement and scattered emergent eucalypts.Similarly, Association 66d is restricted to rocky graniteknolls and escarpments of the coastal fall in the Paluma /Mt Spec area where Leptospermum neglectum is aprominent component mixed with a range of associatedshrub species including Banksia aquilonia andAllocasuarina torulosa.

In the drier northern parts of the bioregion, areas ofskeletal soils may be colonised by deciduous shrubland orlow woodland communities dominated by Cochlospermumgillivraei or Bombax ceiba (66g), or Canarium australianum(66h). These are highly restricted associations, both interms of extent and distribution in the bioregion, althoughthey are much more common in the Cape York Bioregionextending northwards through the Torres Strait Islands toNew Guinea.

Facts and figures

Vegetation alliances

Rock pavement complexesCoastal headland complexes

Current extent in the

bioregion 13,912haArea protected 6,474ha (47%)

VEGETATION COMPLEX AND MOSAICS

OF THE WET TROPICS BIOREGIONRock pavement and coastal headland complexes (vegetation codes 66a-66h)

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Geography

This alliance occurs throughout the bioregion,predominantly on steep coastal escarpments and on thedrier western margins. Its distribution is heavily influenceby skeletal soils with the most extensive occurrencestypically associated with highly weather resistantgeologies including acid volcanic, granitic andmetamorphic rock types. Extensive areas are alsoassociated with the incised middle reaches of the majorriver systems including the Barron, Tully, Herbert,Daintree and Bloomfield Rivers.

Impacts and changes

This formation, being adapted to harsh edaphic conditions,is generally stable and not subject to successional orstructural changes. Colonising species such asAllocasuarina littoralis may proliferate in the absence offire, resulting in a reduction of floristic diversity, althoughthese changes tend to be transient and short term. Moreconcerning changes relate to the proliferation of exoticgrass species, most prominently in coastal areas, wheremolasses grass (Melinis minutiflora) is colonisingextensive areas of rock pavement, displacing nativespecies.

Key values

Uncertain

Threatening processes

• Invasion of exotic species, particularly grasses, in theabsence of regular prescribed burning.

Tenure

Extensive areas conserved in Hinchinbrook Island NP,Tully Falls NP and in the Herbert Gorge area.

Management considerations

• Fire management required in degraded coastal areas

• Requires prevention of extremely hot wildfires whichmay promote colonisation by molasses grass andprevent reestablishment of native species

• Continued prescribed burning regimes on HinchinbrookIsland necessary to prevent domination by Allocasuarinalittoralis.