Global significance of freshwater swamp forest 
13 
Fig. 1 . Conceptual diagram showing the effects of stream morphology, hydrology, vegetation 
and physico-chemistry on each other and on the macroinvertebrate and fish community in 
freshwater swamp forests, specifically in the Nee Soon freshwater swamp forest. 
discharge. The authors identified that changes in pH were related to both streamwater 
level and monthly rainfall. Indeed, the decrease in pH was related to the inundation 
of the streams and an increase in overland flow (Ramirez et al., 2006). Furthermore, 
Ramirez et al. (2006) noted that discharge and pH changed most during the year and 
whilst pH decreased, stream discharge increased. The temporal variation in pH was 
attributed to the increases in the concentration of humic acids suspended in the water 
column during the wet season. Indeed, previous work by Winterbourn & Collier (1987) 
observed low pH levels in many New Zealand streams and attributed this to the large 
inputs of humic acids from surrounding watersheds. Alternatively, temporal variations 
in conductivity were small and were independent of discharge but were related to 
groundwater influence (Ramirez et al., 2006). 
Aquatic flora in freshwater swamp forests 
The environmental conditions of a tropical freshwater swamp forest are similar to those 
of a tropical dryland rain forest, but in general, the tree canopy of the freshwater swamp 
forest is lower than that in the lowland dipterocarp forest (Corner, 1978; Theilade et 
al., 2011). The vegetation structure in freshwater swamp forests is often dependent on 
