Mangrove biodiversity survey south of the Onilahy River - Frontier ...

Methods
Surveys were undertaken in the Lavadanora mangal between November 2001 and February 2002.
Methods were revised from English et al. (1994) as appropriate for this mangal and are outlined
below.
Mapping
• First the mangal was mapped using a GPS (WGS 84 Projection dd°mm.mmm’, Southings 23°,
Eastings 043°). The mapping included the edges of the creeks at high tide and the extent of the
mangal. Edges being defined as where the tree density fell to below one per 100m 2 . Important
points were noted, such as fresh water sources. This map was then used to set out transects. Due
to poor GPS coverage resulting from the proximity of the cliffs at this mangal, compasses and
distance estimation were also used.
Tree density and height measurements
• Transects were conducted at approximately 200m intervals on either side of the creek
perpendicularly to the angle of the creek. The perceived lack of different species zonation in this
mangal making more frequent measurements unnecessary.
• A 10m x 10m quadrat was placed at the beginning of each transect and then every 50m until the
edge of the mangal was reached.
• Within the quadrat the total number of adults, saplings and seedlings for each species present
was recorded. Adults were classified as having a girth at breast height (GHB) greater than 4cm.
Saplings were classified as having a height greater than 1m and a GBH less than 4cm, and
seedlings as having a height less than 1m and a GBH less than 4cm.
• The GBH and the height of the trees were recorded for three adults of each species present.
• The trees closest to the Southwest corner of the quadrats if North of the creek or the Northwest
corner of the quadrat South of the creek were measured. If the stem forked below breast height
each branch was measured as a separate stem.
• The height was measured using a clinometer in addition to being visually estimated. If the trees
were small enough then a measuring tape was used to further increase the accuracy of the results.
Salinity
• Soil salinity is a more accurate measure than water salinity in the creeks, as it is not as tide
dependent. In accordance with this, the salinity of the soil in each of the 35 quadrats sampled
was measured using the following method.
• Soil samples were taken at low tide when the substratum was uncovered.
• They were taken from the middle of each quadrat.
• In the region of 20g of soil was taken from 10cm below the surface to avoid problems associated
with high salinity due to evaporation.
• This was placed into a plastic bag with a piece of waterproof paper with the transect and quadrat
number recorded on it in pencil.
• The bag was then sealed to ensure it was airtight.
• Analyses were carried out within two to three hours to minimise errors associated with
evaporation and condensation.
• The soil was analysed by putting it into a 60cc syringe previously prepared with a piece of filter
paper placed in the bottom of the barrel.
• Water was then squeezed through the filter using the plunger to extract 3-4 drops.
• The drops were analysed for salinity using a refractometer before all the equipment being
cleaned in preparation for the next sample.
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