Journal of the Royal Society of Western Australia, 86:25-30, 2003 
Structure and productivity of inland mangrove stands 
at Lake MacLeod, Western Australia 
J C Ellison 1 & S Simmonds 2 ' 3 
1 School of Geography and Environmental Studies, University of Tasmania, 
Locked Bag 1-376, Launceston, TAS 7250 E Joanna.Ellison@utas.edu.au 
2 Dampier Salt Ltd, PO Box 1619, Karratha, WA 6714 
3 Current address: ERA - Ranger Mine, PO Box 333, Jabiru, NT 0886 
El stuart.simmonds@era.riotinto.com.au 
(Manuscript received March 2002; accepted February 2003) 
Abstract 
Lake MacLeod has the largest area of inland mangroves in the world, where communities of 
stunted Avicennia marina (Forsk) Vierh occur isolated from coastal mangroves. These mangroves 
exist in extremes of environmental stress, mainly related to high salinity, as a consequence of the 
extreme environment associated with their location on the margins of a non-tidal salt lake in an 
arid climate. Characteristics of this unique mangrove system are described, showing an annual 
productivity of 855 g dry wt nr 2 and an average biomass of 121.3 t ha 1 . These are equivalent levels 
to open coastal mangroves in sub-tropical Eastern Australia. Phenological patterns showed a 
maximum production of 3-4 g nr 2 d' 1 associated with fruiting during late summer, and minimum 
leaf loss during the winter period June to September. 
Keywords: mangroves, Avicennia marina, arid, inland, Lake MacLeod, productivity, structure 
Introduction 
Lake MacLeod is a large saline coastal lake located 
approximately 30 km north-north-west of Carnarvon, 
Western Australia. It has an area of 220 000 ha, of which 
permanent waters cover ca 6 000 ha. The salt lake is 
episodically inundated by fresh water, allowing 
development of a unique assemblage of wetland types in 
Australia (Lane et al 1996). These include permanent 
saline wetlands and inland mangrove swamps that are 
maintained by subterranean waterways. The lake is a 
major migration stop-over and drought refuge area for 
shorebirds, and is also one of the most important non- 
tidal stop-over sites in Australia. It also supports 
Australia's and the World's largest inland community of 
mangroves and associated fauna. Lake MacLeod is listed 
on the Register of National Estate and is recognised in 
the Directory of Important Wetlands in Australia (Lane et 
al. 1996). 
Lake MacLeod's mangrove community is the larger of 
only two inland occurrences in mainland Australia; the 
other is also in Western Australia, at Mandora Salt 
Marshes (Beard 1967). The Lake MacLeod mangroves 
occur as low closed-forest to open scrub/shrubland, 
forming narrow margins that fringe water bodies at the 
sinkholes, channels and the central lake. Surrounding 
areas support low open samphire shrubland. There are 
two main areas, 7.5 ha at North Cygnet Pond, and 15 ha 
at South Cygnet Pond (Johnstone 1990). The only 
mangrove species occurring in Lake MacLeod is 
Avicennia marina (Forsk) Vierh, which is the only 
mangrove species to reach this far south on the WA coast 
(Semeniuk 1993). 
© Royal Society of Western Australia 2003 
Mangroves inhabit the intertidal zone of sheltered 
shores in the tropics or sub-tropics. Those that occur 
inland, isolated from the ocean, are very unusual and 
for this reason these rare cases are well described in the 
literature. Because mangrove seeds or propagules are 
dispersed by seawater, these inland locations are 
usually relics of a former sea level, so have geological 
interest. 
Several limestone islands in the Caribbean area have 
inland saline ponds connected with the ocean by 
submarine caves, supporting inland mangroves. In 
Bermuda there are many small mangrove areas, some 
occurring in inland anachaline ponds that exchange 
water with the ocean through submarine caves (Thomas, 
1993). These occur at sea level, and water salinity is 
around 35 %o. Thomas et al. (1992) described biotic 
characteristics of the largest mangrove ponds, finding 
species variability of mangrove and root biota between 
ponds, caused by isolation of communities. In the 
Bahamas, mangroves 50 km inland are described from 
Inagua by Lugo (1981) at three locations with no 
apparent connection with the ocean. The island is 
limestone, and the inland mangrove areas are cut off 
from the ocean by lithified beach ridges. Evaporation 
from the large shallow lakes raises salinity to up to 70 %o, 
which has the effect of stunting the mangrove trees. 
Barbuda has inland mangrove ponds 2-4 km from the 
ocean and separated by Pleistocene beach ridges of 2-4 m 
in height (Stoddart et al. 1973). These inland Rhizophora 
thickets are dense and productive, but tended to be of 
lower height than the 7 m coastal Rhizophora on Barbuda. 
The distribution was interpreted as a geological relic, 
caused by sea-level change. 
In the South Pacific, Woodroffe (1987) described 
inland mangroves on a small island of Tuvalu, 
Nanumanga, where mangroves fringe a water body that 
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