1. Aerial root formation: oxygen absorption from the air
2. Mound root formation: oxygen absorption from the air and nutrient absorption
from litter that accumulates on mound roots.
As described above, peat swamp forests have a dome-shaped topography that is
called a peat dome. The vegetation and the environment between the center and the
periphery of the peat dome are very different (Page et al. 1999). In harsh environments such as anaerobic soil environments caused by flooding, low nutrient availability and decomposition rate conditions (Rahajoe and Kohyama 2003), and low pH
conditions (Yule and Gomez 2009), only species that are adapted to the environment
can survive and develop. The ground in PFSs is not flat, and the trees grow on hills
called hummocks made of tree roots and litter. Some tree species form buttress roots,
and especially large hummocks are found around these roots (Shimamura and
Momose 2005, 2007). Water accumulates inside the hummock and in the hollow
around the buttress roots. The vertical change in hydraulic conductivity from the top
of the hummock to the forest floor and the water storage capacity of the cavity
between the roots limit the variability of the soil water content and retain water inside
the hummock (Herwitz 1988; Dommain et al. 2010).
Furthermore, the peat dome has a convex structure in which the center is flat and
the slope becomes steeper toward the periphery. Many species with buttress roots are
found at the edge of the dome that faces the river. On the other hand, at the center of
the dome, species with prop roots and respiratory roots such as knee roots are
common (Richards 1952; Corner 1978; Wittmann and Parolin 2005), and these
roots suppress the horizontal movement of water less than the buttress roots. For
this reason, the GWL is close to the ground surface at the center of the dome, and
flooding is frequent and is maintained for a long period of time. In this way, the
dome center is dry less often than the dome periphery. The overflowing water moves
to the margin of the dome and is stored by hammocks and buttresses roots. Thus, the
dome creates a structure in which the ground surface is always covered by water. In
other words, not only living trees but also dead tree parts and ground surface
irregularities store and retain large amounts of water on the surface of the ground
in PSFs.
1.7 Adaptation to Nutrient Limitation
As peatlands are extremely nutrient-poor, nutrient cycling (Fig. 1.18) is the key to
nutrient (mainly P, Ca, Mg, and micronutrients) utilization by plants through:
a. Recycling (litter supply and decomposition)
b. Retranslocation (old organs to new organs)
c. Reuse (metabolite reuse in cells).
1 Basic Information About Tropical Peatland Ecosystems
27
2. Mound root formation: oxygen absorption from the air and nutrient absorption
from litter that accumulates on mound roots.
As described above, peat swamp forests have a dome-shaped topography that is
called a peat dome. The vegetation and the environment between the center and the
periphery of the peat dome are very different (Page et al. 1999). In harsh environments such as anaerobic soil environments caused by flooding, low nutrient availability and decomposition rate conditions (Rahajoe and Kohyama 2003), and low pH
conditions (Yule and Gomez 2009), only species that are adapted to the environment
can survive and develop. The ground in PFSs is not flat, and the trees grow on hills
called hummocks made of tree roots and litter. Some tree species form buttress roots,
and especially large hummocks are found around these roots (Shimamura and
Momose 2005, 2007). Water accumulates inside the hummock and in the hollow
around the buttress roots. The vertical change in hydraulic conductivity from the top
of the hummock to the forest floor and the water storage capacity of the cavity
between the roots limit the variability of the soil water content and retain water inside
the hummock (Herwitz 1988; Dommain et al. 2010).
Furthermore, the peat dome has a convex structure in which the center is flat and
the slope becomes steeper toward the periphery. Many species with buttress roots are
found at the edge of the dome that faces the river. On the other hand, at the center of
the dome, species with prop roots and respiratory roots such as knee roots are
common (Richards 1952; Corner 1978; Wittmann and Parolin 2005), and these
roots suppress the horizontal movement of water less than the buttress roots. For
this reason, the GWL is close to the ground surface at the center of the dome, and
flooding is frequent and is maintained for a long period of time. In this way, the
dome center is dry less often than the dome periphery. The overflowing water moves
to the margin of the dome and is stored by hammocks and buttresses roots. Thus, the
dome creates a structure in which the ground surface is always covered by water. In
other words, not only living trees but also dead tree parts and ground surface
irregularities store and retain large amounts of water on the surface of the ground
in PSFs.
1.7 Adaptation to Nutrient Limitation
As peatlands are extremely nutrient-poor, nutrient cycling (Fig. 1.18) is the key to
nutrient (mainly P, Ca, Mg, and micronutrients) utilization by plants through:
a. Recycling (litter supply and decomposition)
b. Retranslocation (old organs to new organs)
c. Reuse (metabolite reuse in cells).
1 Basic Information About Tropical Peatland Ecosystems
27