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Ganl. Bull. Singapore 70 (Suppl. 1) 2018 
Lim Nee Soon (1879-1936), the Nee Soon freshwater swamp forest is located in the 
Central Catchment Nature Reserve, surrounded by the Executive Golf Course in the 
north, Seletar Expressway and Old Upper Thompson Road in the east. Upper and 
Lower Peirce reservoirs in the south, and the southern-most tributary of the Upper 
Seletar Reservoir and the northern-most tributary of the Upper Peirce Reservoir in the 
west (Yeo & Lim, 2011). This area incorporates areas that were previously part of the 
Chan Chu Kang forest reserve (Corlett, 1992), which has allowed it to preserve much 
old-growth vegetation. The Nee Soon freshwater swamp forest is thus the last remnant 
of a larger swamp forest which was previously found along the entire Seletar drainage, 
including the areas surveyed by Corner in Mandai (Comer, 1978; Ng & Lim, 1992; 
O’Dempsey & Chew, 2013). It has probably only survived to the present day by virtue 
of being both included in the Central Catchment Nature Reserve as well as being used 
as a training area for the Singapore Armed Lorces and the presence of military shooting 
ranges nearby (Ng & Lim, 1992). According to Corlett (2011), the freshwater swamp 
forest is concentrated within several shallow valleys that drain towards the Seletar 
River while the elevated areas between the valleys support patches of dryland forest. 
Physical environment of Nee Soon freshwater swamp forest 
The ground surface of most places in Nee Soon freshwater swamp forest is covered 
by a shallow layer of peat and there is some variation in the microtopography of the 
forest (Taylor et al., 2001; Corlett, 2011). Because the water table is so close to the soil 
surface, periodic to semi-permanent flooding can be observed (Yeo & Lim, 2011). In 
addition, depressions in the topography are often saturated with water, forming small 
pools and slow-flowing streams (Turner et al., 1996; Taylor et al., 2001). Usually, 
the clear water in the swamp forest is stained a dark-tea colour, a result of tannin 
leaching from slowly decomposing plant matter under waterlogged soil conditions 
(Yeo & Lim, 2011). Some of the larger streams have bed deposits of coarse-grained 
sand that probably originates from the Triassic Period Bukit Timah granite formation 
that constitutes most of the basement rock below the swamp (Taylor et al., 2001). 
Soil analysis conducted at the Nee Soon freshwater swamp forest in the 
mid-1990s revealed that the first 5 cm of the soil layer was rich in organic matter 
(approaching 80% to 90% loss-on-ignition by mass), though the content decreased 
rapidly beyond that depth to less than 50% loss-on-ignition by mass (Turner et al., 
1996). Hence, the lower layer of soil is not considered to be peat, which has more 
than 90% loss-on-ignition by mass. The anaerobic and waterlogged conditions found 
in the soil of the Nee Soon freshwater swamp forest reduce its rate of decomposition, 
contributing to the richness in its organic matter (Turner et al., 1996). 
Additionally, leaf litter in the Nee Soon freshwater swamp forest was found to 
have a lower level of nutrients such as nitrogen, potassium and phosphorus compared 
to the top 5 cm of soil. This could be caused by the draining of nutrients from the leaf 
litter into the soil (Turner et al., 1996). 
The pH of swamp forest streams and soil water is between 4.6 and 5.5, more 
acidic compared to typical forest streams, and could become more acidic 5 cm below 
the surface of the soil (Turner et al., 1996; Yeo & Lim, 2011). This could be a result of 
