tropical peatland ecosystems. Additionally, land-use change has a similar impact on
tropical peatland ecosystems.
The hypothesized peat formation process (Fig. 1.4) is as follows:
• Phase 1: Mangroves are dominant, indicating that the water in the ecosystem is
mainly sea water. In this stage, nutrients are mainly supplied from the sea.
• Phase 2: Mosaic vegetation is dominant because organic matter accumulates at
the bottom, the sea water supply decreases downstream, and the fresh water (rain
and river flooding) supply increases upstream. In this stage, nutrients are supplied
from the sea water (tidal effect) and river sediments (clay) due to river flooding.
• Phase 3: A freshwater swamp forest dominates, indicating that water is mainly
supplied from rainwater. In this stage, the nutrient supply is very limited because
of the lack of nutrients in rain.
Peat domes develop at the third step due to the poor nutrient supply.
Along diked rivers, tree growth is very good because of the rich nutrients in
organic soils and the lack of water.
In flooding areas along rivers, only grass can grow because of the rich nutrients
(clay supplied by floods) in the organic soils and floodwaters, which cause low
reducing conditions (less than À300 mV redox potential). Thus, the peat depth
decreases.
At the bottom of peat domes, trees can grow well because there are enough water
and sufficient nutrients (approximately 0 mV redox potential). Biomass production
is high, but biomass decomposition is also high because of the high microorganism
activity due to the high nutrient levels. Thus, the peat depth increases.
At the top of peat domes, tree growth is poor, but biomass decomposition is low
because of low microorganism activity due to the low nutrient levels.
Anderson (1964) emphasized that mangrove-based peatlands developed at an
early development stage. However, initial peat formation involves not only mangrove vegetation but also freshwater vegetation upstream (Furukawa and Supiandi
1986), indicating that topography is also important in mangrove formation. The
subsoil under peat soil is different along the vertical profile (from mountains to the
sea) of the dome structure. A common pattern is (1) sandy Podzolic subsoils
upstream, (2) alluvial subsoils, and (3) (potential) acid sulfate subsoils near the sea
(Fig. 1.5). The peat developed from these subsoils is typically (1) inland peat,
(2) intermediate peat, and (3) coastal peat, respectively. After peat degradation,
sandy Podzolic soil and acid sulfate soil appear. These soils are considered problem
soils, because they are extremely nutrient-poor and very acidic (less than pH 3.0) due
to the presence of sulfate (Fig. 1.5).
Thus, between island ridges in the maritime continent of Southeast Asia, peat
dome structures form (Fig. 1.3). In the peat dome structure, as water is supplied only
from rain (precipitation), the nutrient supply is extremely limited.
10
M. Osaki et al.
tropical peatland ecosystems.
The hypothesized peat formation process (Fig. 1.4) is as follows:
• Phase 1: Mangroves are dominant, indicating that the water in the ecosystem is
mainly sea water. In this stage, nutrients are mainly supplied from the sea.
• Phase 2: Mosaic vegetation is dominant because organic matter accumulates at
the bottom, the sea water supply decreases downstream, and the fresh water (rain
and river flooding) supply increases upstream. In this stage, nutrients are supplied
from the sea water (tidal effect) and river sediments (clay) due to river flooding.
• Phase 3: A freshwater swamp forest dominates, indicating that water is mainly
supplied from rainwater. In this stage, the nutrient supply is very limited because
of the lack of nutrients in rain.
Peat domes develop at the third step due to the poor nutrient supply.
Along diked rivers, tree growth is very good because of the rich nutrients in
organic soils and the lack of water.
In flooding areas along rivers, only grass can grow because of the rich nutrients
(clay supplied by floods) in the organic soils and floodwaters, which cause low
reducing conditions (less than À300 mV redox potential). Thus, the peat depth
decreases.
At the bottom of peat domes, trees can grow well because there are enough water
and sufficient nutrients (approximately 0 mV redox potential). Biomass production
is high, but biomass decomposition is also high because of the high microorganism
activity due to the high nutrient levels. Thus, the peat depth increases.
At the top of peat domes, tree growth is poor, but biomass decomposition is low
because of low microorganism activity due to the low nutrient levels.
Anderson (1964) emphasized that mangrove-based peatlands developed at an
early development stage. However, initial peat formation involves not only mangrove vegetation but also freshwater vegetation upstream (Furukawa and Supiandi
1986), indicating that topography is also important in mangrove formation. The
subsoil under peat soil is different along the vertical profile (from mountains to the
sea) of the dome structure. A common pattern is (1) sandy Podzolic subsoils
upstream, (2) alluvial subsoils, and (3) (potential) acid sulfate subsoils near the sea
(Fig. 1.5). The peat developed from these subsoils is typically (1) inland peat,
(2) intermediate peat, and (3) coastal peat, respectively. After peat degradation,
sandy Podzolic soil and acid sulfate soil appear. These soils are considered problem
soils, because they are extremely nutrient-poor and very acidic (less than pH 3.0) due
to the presence of sulfate (Fig. 1.5).
Thus, between island ridges in the maritime continent of Southeast Asia, peat
dome structures form (Fig. 1.3). In the peat dome structure, as water is supplied only
from rain (precipitation), the nutrient supply is extremely limited.
10
M. Osaki et al.