6.1.2 Carbon System in the Tropics
In the tropics, the high solar radiation energy is ameliorated by water functions, the
water cycle and the water stock. High solar radiation energy enhances the carbon
functions, carbon cycle (i.e., assimilation and decomposition) and carbon stock (i.e.,
carbon sequestration). As carbon functions are interrelated with water, once one of
these resources is lost, both systems will immediately collapse.
6.1.2.1 Tropical Rainforests
The reduction in tropical rainforests (Fig. 6.1), located in the equatorial belt, has
been increasing annually, leading to extinction. Tropical rainforests can be characterized as being hot (mean temperatures between 20 and 29
C and no months with a
mean temperature below 18
C) and wet (high rate of precipitation and high
humidity, with annual rainfall between 1800 and 2500 mm) (Smith 2019).
Although the climate supporting tropical rainforests is perpetually hot, temperatures never reach high values due to high levels of cloud cover, which limit the mean
number of sunshine hours per day to between four and six (Smith 2019). The winds
are usually light; mean wind speeds are generally less than 10 km/h and less than
5 km/h in many areas (Smith 2019). Thus, photovoltaic (PV) power generating
systems and wind power generation are not suitable for the conditions found in
tropical rainforests and the tropics.
The moist and hot climatic conditions of the tropics lead to deep weathering of
rocks and the development of deep, typically reddish soil profiles, rich in insoluble
sesquioxides of iron and aluminum, commonly referred to as tropical red earths.
Additionally, as precipitation in tropical rainforest regions exceeds evapotranspiration at almost all times, a nearly permanent surplus of water exists in the soil; this
surplus moves downward through the soil into streams and rivers on valley floors,
causing nutrient leaching (Smith 2019). Due to this nutrient condition, most roots are
concentrated in the uppermost soil layers, where nutrients become available from the
decomposition of fallen dead leaves and other organic litter (Smith 2019).
Thus, it is hypothesized that tropical peatlands are climax ecosystems of tropical
rainforests and are formed as a result of (1) high water reservoirs, which are due to
high rates of precipitation and geographical topography, including the plains around
the Maritime Continent (i.e., the fringe of islands in the southeastern part of the
continent) and the saucer-like shape of basins (e.g., the Amazon and Congo), and
(2) extreme deficiencies in nutrients, which are due to water being supplied mainly
by rain (which does not carry nutrients) and periodic floods (which contain clay).
Less than 50% of the world’s tropical forests remain standing today, with much of
the remaining forest cover seriously affected by logging, fires, fragmentation,
mining, and hunting (Malhi et al. 2014; Lewis et al. 2015). The loss and degradation
of tropical forests have strong negative consequences for biodiversity, climate
206
M. Osaki et al.
In the tropics, the high solar radiation energy is ameliorated by water functions, the
water cycle and the water stock. High solar radiation energy enhances the carbon
functions, carbon cycle (i.e., assimilation and decomposition) and carbon stock (i.e.,
carbon sequestration). As carbon functions are interrelated with water, once one of
these resources is lost, both systems will immediately collapse.
6.1.2.1 Tropical Rainforests
The reduction in tropical rainforests (Fig. 6.1), located in the equatorial belt, has
been increasing annually, leading to extinction. Tropical rainforests can be characterized as being hot (mean temperatures between 20 and 29
C and no months with a
mean temperature below 18
C) and wet (high rate of precipitation and high
humidity, with annual rainfall between 1800 and 2500 mm) (Smith 2019).
Although the climate supporting tropical rainforests is perpetually hot, temperatures never reach high values due to high levels of cloud cover, which limit the mean
number of sunshine hours per day to between four and six (Smith 2019). The winds
are usually light; mean wind speeds are generally less than 10 km/h and less than
5 km/h in many areas (Smith 2019). Thus, photovoltaic (PV) power generating
systems and wind power generation are not suitable for the conditions found in
tropical rainforests and the tropics.
The moist and hot climatic conditions of the tropics lead to deep weathering of
rocks and the development of deep, typically reddish soil profiles, rich in insoluble
sesquioxides of iron and aluminum, commonly referred to as tropical red earths.
Additionally, as precipitation in tropical rainforest regions exceeds evapotranspiration at almost all times, a nearly permanent surplus of water exists in the soil; this
surplus moves downward through the soil into streams and rivers on valley floors,
causing nutrient leaching (Smith 2019). Due to this nutrient condition, most roots are
concentrated in the uppermost soil layers, where nutrients become available from the
decomposition of fallen dead leaves and other organic litter (Smith 2019).
Thus, it is hypothesized that tropical peatlands are climax ecosystems of tropical
rainforests and are formed as a result of (1) high water reservoirs, which are due to
high rates of precipitation and geographical topography, including the plains around
the Maritime Continent (i.e., the fringe of islands in the southeastern part of the
continent) and the saucer-like shape of basins (e.g., the Amazon and Congo), and
(2) extreme deficiencies in nutrients, which are due to water being supplied mainly
by rain (which does not carry nutrients) and periodic floods (which contain clay).
Less than 50% of the world’s tropical forests remain standing today, with much of
the remaining forest cover seriously affected by logging, fires, fragmentation,
mining, and hunting (Malhi et al. 2014; Lewis et al. 2015). The loss and degradation
of tropical forests have strong negative consequences for biodiversity, climate
206
M. Osaki et al.