Conservation recommendations for Nee Soon 
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Vegetation ecology 
Although the field study found that soil conditions appeared to be more important 
than the presence of open water in structuring tree communities, experiments with 
seedlings showed that for three of the five species, flooding had a significant effect 
on growth responses but not the soil type. Taken together, these results suggest that 
flooding leads to the formation of the tree community structure and the accompanying 
soil properties in the freshwater swamp forest over time. Seedlings growing in the 
swamp forest substrate are likely to be more resilient against short-term droughts. 
Many nationally uncommon and rare plant species are restricted to the swampy 
parts of the Nee Soon catchment. The catchment is also a hotspot of new plant 
records and rediscoveries of species that have previously been presumed to be extinct 
in Singapore. The Nee Soon freshwater swamp forest is therefore of high floristic 
conservation value locally (Chong et al., 2018; Clews et al., 2018). 
The vegetation ecology team predicts that non-swamp plant species are more 
vulnerable than swamp species to anticipated changes in the hydrology of the Nee 
Soon catchment in the future. In some sense, this may be good news, as the swamp 
flora is generally more unusual and tends to be locally rarer. It is expected that about 
2-4 weeks may elapse from the onset of a severely receded water table in originally 
swampy areas following extreme drought, before mass die-offs of seedlings will occur 
so this provides some buffer time for action to be taken, for example, for manual 
irrigation to be set up. However, the time lag periods for saplings and mature trees 
were not investigated during the study. It could be anticipated that the deeper roots 
of larger trees would provide them with a longer buffer period, but water stress might 
also be amplified. 
An ordination analysis was conducted to investigate the relationship between the 
tree community and soil and hydrology. It was only a cross-sectional study and should 
be viewed as correlative rather than causal. To investigate the impacts of drought or 
extreme flooding on mature trees would require either of two approaches: 
1) field manipulations of precipitation (e.g. using rain screens) and hydrology 
(e.g. digging soil trenches or creating artificial flooding) followed by monitoring of 
trees. “Drought-Net” is a global network of study sites that are using standardised 
methods such as these to artificially create drought-like conditions for plants. However, 
they lack partner sites in forest biomes due to the logistic and operational difficulties 
of creating rain screens over a forest canopy. Additionally, given that the Nee Soon 
freshwater swamp forest is the last substantial tract of this forest type in Singapore, 
there would be concerns whether such large-scale manipulations within the forest 
could cause more harm than the resulting science could be beneficial. Tree coring to 
provide direct measurements of sap flow could not be carried out during this study for 
the same reason. A possible solution is to find alternative patchy freshwater swamp 
areas outside nature reserves, which are of lower conservation value, for hydrological 
manipulation and sap flow experiments. 
2) Long-term monitoring of soil hydrology coupled with tree health is the other 
approach, but will require a long time to accrue useable data, and will depend on 
whether different hydrological conditions will occur in the sampled areas over the 
