vegetation types, which tend to go dormant (Wang-Erlandsson et al. 2016). Trees
reduce water erosion by improving water infiltration, reducing impacts by water
droplets, intercepting rain, and physically stabilizing soil with their roots and leaf
litter (Zuazo and Pleguezuelo 2007).
With deeper roots, trees can both store and access more water in the soil, which
they use for transpiration during periods without rain (Teuling et al. 2010) and to tap
into groundwater resources (Fan et al. 2017; Sheil 2014).
6.2.2 Model of the Water–TREE–Carbon Linkage
in the Tropics
The sun provides energy (340 W/m
2 , Stephens and L’Ecuyer 2015), some of which
is reflected or absorbed by the atmosphere, with and almost 40% arriving at the
earth’s surface (i.e., the ground or sea). This energy returns to the atmosphere
through evaporation, convection, and thermal radiation (Lindsey 2009). This energy
is the origin of climate, animal and plant life, and carbon, water, and nutrient cycling.
As the earth is spherical and its rotational axis is on a tilt, the earth is not evenly
heated. At the same time, reflection into space from the earth depends on location.
These imbalances in solar illumination and albedo cause net heating imbalances. In
the tropics, there is a net energy surplus, because the amount of heat absorbed (input)
is larger than the amount of heat radiated (output). However, in the poles, the output
is larger than the input. This heat imbalance, that is, the temperature difference,
causes the circulation of the atmosphere and oceans. Seawater and the atmosphere
are the working fluids of the heat engine.
Tropical forests have important functions, and these functions are also driven by
the sun. Ellison et al. (2017) summarized the effects of forests on water and climate
at different scales (from local to continental): forests can (1) provide a link between
rainfall and water availabilitys, (2) transport water, (3) regulate temperature (i.e.,
cool regions), (4) regulate water supplies, (5) enhance biodiversity, and (6) store
carbon. In regard to regulating temperature (i.e., number 3), Hesslerová et al. (2013)
measured the surface temperature of shallow ponds, forests, harvested meadows, wet
meadows with ground water, and so on, and found that the temperature in forests
(21.7–22.6
C) is lower than that in shallow ponds (25.6
C) and that the temperature
in harvested meadows (28.0
C) is higher than that in forests. There is an interesting
theory regarding points (1) and (2): the optimum tree cover theory (Ilsted et al.
2016). This theory states that groundwater recharge is the highest at a moderate tree
density. As tree density decreases, surface runoff and evaporation from soil are
higher. However, as tree density increases, infiltration and transpiration from trees
are higher. Therefore, groundwater recharge is the highest at an optimum tree
density.
The world’s largest regional rainfall, which occurs over the IMC (Indonesian
Maritime Continent), has often been explained in terms of the seawater surrounding
216
M. Osaki et al.
reduce water erosion by improving water infiltration, reducing impacts by water
droplets, intercepting rain, and physically stabilizing soil with their roots and leaf
litter (Zuazo and Pleguezuelo 2007).
With deeper roots, trees can both store and access more water in the soil, which
they use for transpiration during periods without rain (Teuling et al. 2010) and to tap
into groundwater resources (Fan et al. 2017; Sheil 2014).
6.2.2 Model of the Water–TREE–Carbon Linkage
in the Tropics
The sun provides energy (340 W/m
2 , Stephens and L’Ecuyer 2015), some of which
is reflected or absorbed by the atmosphere, with and almost 40% arriving at the
earth’s surface (i.e., the ground or sea). This energy returns to the atmosphere
through evaporation, convection, and thermal radiation (Lindsey 2009). This energy
is the origin of climate, animal and plant life, and carbon, water, and nutrient cycling.
As the earth is spherical and its rotational axis is on a tilt, the earth is not evenly
heated. At the same time, reflection into space from the earth depends on location.
These imbalances in solar illumination and albedo cause net heating imbalances. In
the tropics, there is a net energy surplus, because the amount of heat absorbed (input)
is larger than the amount of heat radiated (output). However, in the poles, the output
is larger than the input. This heat imbalance, that is, the temperature difference,
causes the circulation of the atmosphere and oceans. Seawater and the atmosphere
are the working fluids of the heat engine.
Tropical forests have important functions, and these functions are also driven by
the sun. Ellison et al. (2017) summarized the effects of forests on water and climate
at different scales (from local to continental): forests can (1) provide a link between
rainfall and water availabilitys, (2) transport water, (3) regulate temperature (i.e.,
cool regions), (4) regulate water supplies, (5) enhance biodiversity, and (6) store
carbon. In regard to regulating temperature (i.e., number 3), Hesslerová et al. (2013)
measured the surface temperature of shallow ponds, forests, harvested meadows, wet
meadows with ground water, and so on, and found that the temperature in forests
(21.7–22.6
C) is lower than that in shallow ponds (25.6
C) and that the temperature
in harvested meadows (28.0
C) is higher than that in forests. There is an interesting
theory regarding points (1) and (2): the optimum tree cover theory (Ilsted et al.
2016). This theory states that groundwater recharge is the highest at a moderate tree
density. As tree density decreases, surface runoff and evaporation from soil are
higher. However, as tree density increases, infiltration and transpiration from trees
are higher. Therefore, groundwater recharge is the highest at an optimum tree
density.
The world’s largest regional rainfall, which occurs over the IMC (Indonesian
Maritime Continent), has often been explained in terms of the seawater surrounding
216
M. Osaki et al.