Ellison & Simmonds: Inland mangroves at Lake MacLeod 
Figure 2. Aerial photograph of Cygnet Pond showing the 
locations of the three mangrove monitoring sites. Photo 5142 of 
Minilya (SF49-16) 16/06/95, Western Australian Department of 
Land Administration. 
relationships established by Clough et al. (1997) between 
stem diameter and above-ground biomass, for the multi¬ 
stemmed trees of Avicennia marina found in arid northern 
WA. Their procedure treats each stem as a discrete tree 
that shares a proportion of the butt and other elements 
common to all stems. They measured stem diameters of 
trees located at Port Hedland, Dampier and Exmouth 
Gulf, at a height of 10-15 cm above the stem junction, 
then cut the trees and divided them into leaves, branches, 
stems and butts. From these measurements they 
determined an allometric equation that estimates tree 
biomass from stem measurement (Table 2 of Clough et al. 
1997); log(W) = -0.7506 + 2.299 log (D) where W is dry 
weight (kg) and D is stem diameter (cm). Clough et al 
(1997) pointed out that it is largely a question of 
semantics whether or not the multi-branched architecture 
of arid mangrove trees should be regarded as multi¬ 
stemmed or simply multi-branched. The distinction is 
irrelevant if the allometric relationship is being used to 
estimate total above-ground biomass or the above¬ 
ground biomass of all woody parts of the tree (trunks 
and branches); it is potentially an issue only if separate 
estimates of stem biomass and branch biomass are 
needed. 
Monitoring Sites 
Permanent plots for monitoring of mangrove 
community structure were established in December 1997 
at three representative sites within the Lake MacLeod 
mangrove system. The sites (Fig 2) encompass the 
variability of mangrove types found at Lake MacLeod, of 
fringing mangroves close to the vents (site 1), on a mid¬ 
lake island (site 2), and fringing the main water body at 
distance from the vents (site 3). 
Three replicate permanent monitoring plots, each of 
10 x 10 meters, were established at each site location. All 
trees and seedlings within the plots were tagged and 
girth measured. Where trees had multiple branches, 
which occurred in the majority, all were tagged and 
measured. 
Litter fall was measured to quantify vegetative 
production and phenology. In each plot at each site, two 
1 m 2 litter catchers were hung below the mangrove 
canopy (Saenger & Snedaker 1993). These were emptied 
each quarter, and the catch oven dried at 60 °C for 2 
days, then sorted and weighed. Given the aridity of the 
Lake MacLeod site, it was possible to empty the litter 
traps at periods longer than monthly (which was not 
feasible owing to remoteness and poor access). Trees 
were re-measured annually, and crown cover and crown 
density were also estimated in November 1999 to give 
percent foliage cover (Daubenmire 1959). 
Mean tree density and tree height were calculated for 
each site from the three replicates at each site. Leaf litter 
data were averaged for the 6 litter catchers at each site, 
and expressed in dry weight (g) per day for each 
collection period. Annual variation in production and 
phenology were analysed from the period September 
1998 to September 1999, when collections were most 
regular. 
Biomass was calculated using the allometric 
Results 
The mangroves of Lake MacLeod form a narrow 
margin around permanent ponds, of usually less than 20 
m in width, with dense shrub growth. At all sites a 
distinct zonation in Avicennia physiognomy is apparent. 
The most developed zone is of tall, dense shrubs fringing 
the water body (Fig 3). The width of this zone is 
generally 10 m or less, but at Goat Bay (Site 3) the width 
extended to 50 m in places. The shrub height and zone 
width of the taller mangroves is greater on shoreline 
promontories than bays. Adjacent to the Lake MacLeod 
water bodies, the density of Avicennia pneumatophores is 
far higher than for Avicennia on the open coast (Fig 3), 
indicating low oxygen levels in the soil and interstitial 
water. This is also a feature of inland mangroves of 
Bermuda (Thomas 1993), and could be caused by the lack 
of aeration of mangrove mud without tidal movement. 
Behind the shoreline zone is a sharp demarcation from 
dense mangrove cover to domination by open salt flat. 
Figure 3. Avicennia marina forest fringing Lake MacLeod at site 
2, showing multi-stemmed architecture, very dense 
pneumatophores, and an eroding shore. 
27 
