Appendix 2 - Vegetation Communities and Regional Ecosystems

an attempt to better describe the landscape and provide a more comprehensive ecological
analysis, a number of land zone sub-groupings have been recognised.
Sub-groupings, as listed in Table 7, are characterised in respect to a rock types specific
ecological properties. Rhyolite (R), which is extensive on the inner group of islands (including
Muralug), is generally the least fertile grouping, being fine grained, and resilient to weathering.
Granites weather to form sandy soils which are relatively well-drained, and can be relatively
fertile depending on the percentage of iron and magnesium rich mineral in the parent rock. The
Badu Granite, which comprises a significant proportion of the Badu, Moa, Dauan and Iama land
masses, is relatively rich in biotite and derived soils are of moderate fertility (as a generalisation).
By definition, diorite is richer in iron and magnesium rich minerals than both granite and rhyolite,
and derived soils are of moderate fertility. This feature is a useful indicator to assist
differentiation of forest types, for example, some of the best-developed examples of vine forest
on foothills occupy diorite knolls and talus slopes on the south eastern-side of Muralug Island.
A final classification recognises altered acid plutonic rocks classified as MG, and is indicative of
rocks that have been hardened through superheating during subsequent intrusive events. These
rocks, generally termed hornfels, are extremely resistant to weathering and often manifest in the
landscape as rock piles and knolls comprised of boulder talus as on Moa Island. Although a
metamorphic rock on a generic level, hornfels is grouped within Land Zone 12 in recognition of
the limited chemical change parent material undergoes during the heating process.
5.2 Regional Ecosystem Descriptions and Rationale for
Classification
This section provides descriptive notes on the occurrence and characteristics of RE’s in the study
area. Features of each RE are discussed in relation to component vegetation communities with
recognition of some marked structural and floristic variations which may occur within individual
RE’s. It should also be noted that individual vegetation communities may be recorded in a range
of regional ecosystems dependant on geological association.
5.2.1 Regional Ecosystem 3.1.1
Description: Closed forest of Rhizophora stylosa ± Bruguiera gymnorhiza. Occurs as outer
mangroves.
Status: Not of Concern
Vegetation Communities: 24a (co), 24b, 24d, 12b
Reference Sites: 41 Quaternary
This is a highly complex and variable RE occupying intertidal areas, generally on the seaward
fringe of mangroves where tidal exchange is greatest, although may be attenuated well inland
along estuarine drainage systems. All islands sampled with the exception of the Coral Cays have
some development of this regional ecosystem on their shorelines, although the most extensive
occurs on the northern islands of Saibai and Boigu, as well as mangrove islands of Zagai, Buru
and Sassie. The major component is open to closed forest although a range of structural
variations including closed shrubland, mangrove woodland and low open forest have been
included in the classification. As such, VC24a the major component of this RE is described as a
mangrove forest, woodland and shrubland complex. Vegetation Community 24d is a purer
expression of RE3.1.1 mapped on the mangrove tidal islands of Sassie and Buru.
3d Environmental – Torres Strait Regional Ecosystem Mapping Project – August 2008
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