Global significance of freshwater swamp forest 
11 
conversion to agriculture has led to severe degradation and loss of ecological and 
biological diversity (Rijksen & Peerson, 1991; Hansen et al., 2009; Yule, 2010). 
The conceptual model presented in this review explores the direct and indirect 
effects of hydrology, physico-chemistry, stream morphology, and vegetation on the 
macroinvertebrate and fish co mm unities. 
The following sections will explore and review the hydrology, physico- 
chemistry, as well as both the aquatic flora and fauna in freshwater swamp forests in 
Southeast Asia. Owing to the dearth of studies investigating freshwater swamp forests 
specifically, the literature concerning peat swamp forests was also incorporated, as 
peat swamps are the habitat most similar to freshwater swamp forests in Southeast 
Asia. 
Hydrology in freshwater swamp forests 
How water flows is a major determinant of geomorphological, biological and bio- 
geomorphological processes and functions within aquatic ecosystems (Poff et al., 
1997; Bunn & Arthington, 2002; Davidson et al., 2012; Fig. 1). By influencing 
geomorphology, flow plays a major role in determining spatial and temporal benthic 
community structure (Poff & Allan, 1995; Bunn & Arthington, 2002; Mim s & Olden, 
2013). For example, Leigh & Sheldon (2009) found that hydrological connectivity 
had a major effect on macroinvertebrate assemblages, with highly connected water 
bodies displaying greater macroinvertebrate diversity than isolated water bodies, 
which tended to have fewer diverse assemblages and were dominated by a handful 
of taxa. Similar effects have been noted in tropical systems where wet or monsoon 
season flooding has resulted in greater proportions of migratory species and changes in 
community assemblages (da Silva et al., 2010). On a smaller scale, changes in physical 
habitat caused by alterations in flow regime can increase habitat heterogeneity and 
thereby increase species diversity (Downes et al., 1998; Bunn & Arthington, 2002). 
Furthermore, a highly heterogeneous habitat is able to provide refugia for species 
during periods of disturbance such as flooding or drought (Bunn & Arthington, 2002; 
Negishi et al., 2002). In ecosystems where water availability can vary dramatically 
between seasons, such refugia can become extremely important (Brown, 2003; Leigh 
et al., 2010). 
In some tropical systems there is pronounced seasonal variation in the hydrologic 
regime between the monsoon and dry seasons (Douglas et al., 2005; Mitsch et al., 
2010), though with caveats for Singapore’s meteorology as described below. When 
the monsoon season arrives, heavy rains can create flood pulses which integrate 
terrestrial and aquatic systems (Davidson et al., 2012). Junk et al. (1989) stressed the 
importance of seasonal flood pulses through effects such as over-bank flooding, which 
strongly influences biological community structure through allochthonous inputs and 
changing of the physical habitat (Douglas et al., 2005; Davidson et al., 2012). For 
example, in Brazilian floodplains da Silva et al. (2010) found that turbid and anoxic 
water conditions dominated in the high water season compared to low or falling water 
