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Publication Type J
Authors Semeniuk, V. and P. A. S. Wurm
Title MANGROVES OF THE DAMPIER ARCHIPELAGO WESTERN AUSTRALIA
Source Journal of the Royal Society of Western Australia
Abstract The mangrove habitats, vegetation assemblages and vegetation structural and floristic types along the coast of the Dampier Archipelago occur in definitive and discrete locations that are related to coastal evolution, geomorphology, and a range of physico-chemical and biological factors. The disposition and evolution of coastal environments has been determined by the interaction of the oceanography/meteorology with the ancestral geomorphology of the Precambrian rock hinterland. The large scale coastal geomorphic units which have developed are: straight sandy and sandy and rocky coasts; embayments and straits; and connective tidal lands. Medium scale, intertidal geomorphic units developed within the large scale setting include: rocky shores, gravelly, sandy and muddy tidal flats, spits and cheniers, sandy beaches, tidal creeks, shoals, tidal lagoons, mid and high tidal alluvial fans, limestone pavements and the hinterland margin. Habitats for mangroves and an associated mangrove assemblage are developed on these geomorphic units in response to salinity, tidal level and substrate. Various selected areas in the region are described to provide an indication of the variability of mangrove habitats and vegetation. There is a heterogeneous distribution of habitats in each of the areas to the small and medium scale, with the embayment setting containing the most heterogeneous aggregate of habitats. However, while small scale heterogeneity is emphasised it is also noted that many habitats are recurring. For instance, rocky shores are widespread units and may be considered to be the most common habitat in the region. Other units, while discrete in occurrence and limited in area, also are quite widespread when viewed regionally. Mangroves are most luxurant, abundant, and diverse in embayments and connective tidal-lands. The most species rich, zoned mangal occurs in two main environments: (1) on some alluvial fans and (2) peripheral to sandy terrains, such as spits and beaches. Six mangrove speceis occur in the Dampier Archipelago area: Avicennia marina, Aegialitis annulata, Aegiceras corniculatum, Bruguiera exaristata, Ceriops tagal and Rhizophora stylosa. Environmental forcing factors can only influence three aspects of mangrove populations: their composition, structure and maintenance. Since there is only a small species pool in the region, environmental gradients and differences between habitats therefore are reflected in a variety of structural and physiognomic types within the limited floristic assemblage. Although the vegetation, comprised of structural/floristic units, that occurs on a given habitat may vary locally, generally recurring patterns of distribution can be determined. The muddy tidal flats support scrub of a seaward Rhizophora zone and a landward Avicennia zone. Sandy tidal flats support a physiognomically-zoned Avicennia, grading from forest at its seaward edge, through scrub to heath or low shrubland. Rocky/bouldery shores support a monospecific Avicennia shrubland or scrub. Spits and cheniers support zones of Avicennia shrubland, Ceriops scrub, Bruguiera scrub and Avicennia scrub. Beaches support an Avicennia scrub which may be mixed with Ceriops, Bruguiera, Aegialitus and Aegiceras. Avicennia scrub occurs along the hinterland margin, along high tidal dune margins, and along high tidal lagoons. Tidal creek banks are vegetated by Rhizophora and/or Avicennia forest or scrub. Small accretionery shoals in tidal creeks support an Aegiceras scrub with an understorey of Aegialitis. Limestone pavements support an Avicennia shrubland. Gravelly tidal flats support an Avicennia scrub. High tidal alluvial fans support a mixed Ceriops and Avicennia shrubland or scrub. Mid-tidal alluvial fans support a physiognomically zoned Avicennia scrub with patches of Rhizophora scrub. The approach adopted in this study has tended to emphasise the physico-chemical factors that lead to coastal heterogeneity and habitat variability at various scales of reference. Thus this paper provides a framework within which the distribution and internal heterogeneity of mangrove formations may be understood by resolution of the essential features of habitat evolution, maintenance and distribution. Mangroves then are viewed simply as opportunistic inhabitants that respond to the variable environment by changes in their composition, physiognomy, structure and maintenance strategies.
Author Address SEMENIUK V; 21 GLENMERE RD, WARWICK, WA 6024, AUSTRALIA
ISSN 0035-922X
ISBN 0035-922X
Year Published 1987
Volume 69
Issue 2
Beginning Page 29-87
Unique Article Identifier BCI:BCI198885066865
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