Hobbie et al. 2017). According to Ngo et al. (1987, 1991b) and Nhan et al. (1996),
assemblages of peat-forming plants in ancient coastal swamps are mainly composed
of angiosperms, which are woody plants growing in saline swamps in the past, as
Rhizophora sp., Bruguiera sp., Avicennia sp. Anacardiaceae, Sommeratia sp.,
Excoecaria sp., Quercus sp., Nypa fruticans, Cyperaceae, Rutaceae, Fagaceae,
Euphorbiaceae, Leguminosae. Peat-forming plants in ancient abandoned river
courses belong to herbaceous plants which grew in freshwater marsh environments.
They are mainly composed of groups of ferns as Microsorrium sp., Stenochlaena
palustris, Acrostichum aureum, Polypodiaceae, Cyatheaceae, Blechnaceae,
Cupressaceae.
The cross-sections of peat profiles recorded two various stages of peat formation
in U Minh swamps: (1) Lower peat layer composed of typical remnants of mangroves; their predominance diminished in the upper peat layer and (2) in the upper
peat layer, typical plants were Melaleuca leucadendron, Astonia spatula, Nypa
fruticans, fern group also recorded including species of Polypodiaceae,
Stenochlaena palustris, Polypodium sp., and species of ferns in the top layer. The
accumulated succession of peat-forming plants identified from bottom to upper
layers showed that at the beginning peats had been formed in saline-affected
swamps, which were then converted into the freshwater environment after being
isolated due to expanded accretion of the coastal plains. Based on field observation,
Safford et al. (2009) recorded many large stumps of other tree species apparently
preserved in situ, but now either long extinct or historically too rare to have been
described as typical of the area.
Peat is formed by decomposition and accumulation process of buried organic
matters, which do not fully decay in acidic and anaerobic conditions, derived from
plant materials that grow on the land, which is influenced by the dry and wet season
periods (Charman 2002; Craft 2015), and the rate of accumulation of peat depends
on the physical and hydrologic conditions of various wetlands. Peat-swamp forest
soils are waterlogged most of the year and the anaerobic, nutrient-poor conditions
prevent the complete decomposition of forest litter to form peat (Finlayson and
Moser 1991; Warren et al. 2016). However, the slow rate of peatland growth and
development is associated with waterlogged and anaerobic subsurface conditions
(FAO 1988). According to Charman (2002), peat formation occurs in a long period
with the formation rate of about 1 mm/year, and Dommain et al. (2011) stated longterm average rates of peat accumulation are relatively slow, ranging from 0.5 to
1.8 mm/year. Based on the radiocarbon dating data, Nhan et al. (1996) estimated the
average rate of peat accumulation was ranged from 1 to 2 mm/year. The estimated
peat accumulation rate is similar to those on peatlands in Southeast Asia.
29.2.2 Distribution of Peatlands
In the world, peatlands are referred to by various names such as bogs, fens, and mires
(Craft 2015). Based on the FAO’s World reference base for soil resources (FAO
780
Q. P. Le and T. X. Le
assemblages of peat-forming plants in ancient coastal swamps are mainly composed
of angiosperms, which are woody plants growing in saline swamps in the past, as
Rhizophora sp., Bruguiera sp., Avicennia sp. Anacardiaceae, Sommeratia sp.,
Excoecaria sp., Quercus sp., Nypa fruticans, Cyperaceae, Rutaceae, Fagaceae,
Euphorbiaceae, Leguminosae. Peat-forming plants in ancient abandoned river
courses belong to herbaceous plants which grew in freshwater marsh environments.
They are mainly composed of groups of ferns as Microsorrium sp., Stenochlaena
palustris, Acrostichum aureum, Polypodiaceae, Cyatheaceae, Blechnaceae,
Cupressaceae.
The cross-sections of peat profiles recorded two various stages of peat formation
in U Minh swamps: (1) Lower peat layer composed of typical remnants of mangroves; their predominance diminished in the upper peat layer and (2) in the upper
peat layer, typical plants were Melaleuca leucadendron, Astonia spatula, Nypa
fruticans, fern group also recorded including species of Polypodiaceae,
Stenochlaena palustris, Polypodium sp., and species of ferns in the top layer. The
accumulated succession of peat-forming plants identified from bottom to upper
layers showed that at the beginning peats had been formed in saline-affected
swamps, which were then converted into the freshwater environment after being
isolated due to expanded accretion of the coastal plains. Based on field observation,
Safford et al. (2009) recorded many large stumps of other tree species apparently
preserved in situ, but now either long extinct or historically too rare to have been
described as typical of the area.
Peat is formed by decomposition and accumulation process of buried organic
matters, which do not fully decay in acidic and anaerobic conditions, derived from
plant materials that grow on the land, which is influenced by the dry and wet season
periods (Charman 2002; Craft 2015), and the rate of accumulation of peat depends
on the physical and hydrologic conditions of various wetlands. Peat-swamp forest
soils are waterlogged most of the year and the anaerobic, nutrient-poor conditions
prevent the complete decomposition of forest litter to form peat (Finlayson and
Moser 1991; Warren et al. 2016). However, the slow rate of peatland growth and
development is associated with waterlogged and anaerobic subsurface conditions
(FAO 1988). According to Charman (2002), peat formation occurs in a long period
with the formation rate of about 1 mm/year, and Dommain et al. (2011) stated longterm average rates of peat accumulation are relatively slow, ranging from 0.5 to
1.8 mm/year. Based on the radiocarbon dating data, Nhan et al. (1996) estimated the
average rate of peat accumulation was ranged from 1 to 2 mm/year. The estimated
peat accumulation rate is similar to those on peatlands in Southeast Asia.
29.2.2 Distribution of Peatlands
In the world, peatlands are referred to by various names such as bogs, fens, and mires
(Craft 2015). Based on the FAO’s World reference base for soil resources (FAO
780
Q. P. Le and T. X. Le