PB2: Extinction rate (red) and loss of ecological functions (not yet quantified)
PB3: Land-use change (yellow)
PB4: Freshwater consumption (green)
PB5: Biogeochemical flows (nitrogen and phosphorus) (red)
PB6: Ocean acidification (green)
PB7: Atmospheric aerosol loading (not yet quantified)
PB8: Stratospheric ozone depletion (green)
PB9: Novel entities (not yet quantified).
Each color in parentheses shows the following:
Green: Below the boundary (safe),
Yellow: In zone of uncertainty (increasing risk) and
Red: Beyond the zone of uncertainty (high risk).
Climate change is one of the key elements of “planetary boundaries” (Rockstrom
et al. 2009), for which El Niño is an outstanding indicator of climate change. El Niño
seriously affects tropical zones (Hamada et al. 2002, 2012; Yamanaka 2016, 2020).
The annual terrestrial GPP (gross primary production) across latitudes (in 0.5
bands) is the highest in tropical zones regardless of the different models used for the
calculations (Beer et al. 2010). Tropical forests and savannas account for 60% of
terrestrial GPP (123 Æ 8 Pg C year
À1 ). The GPP over 40% of the vegetated land on
Earth is positively associated with precipitation. Additionally, Beer et al. (2010)
show high spatial correlation between GPP and precipitation, suggesting the existence of missing processes or feedback mechanisms that attenuate the response of
vegetation to climate. On the other hand, as the precipitation and cloud distribution
are the highest in tropical zones (Yamanaka 2016; Wang et al. 2019; Ramage 1968;
Worden et al. 2007), the highest precipitation rate should result in the highest GPP.
Thus, the tropical zone is one kind of boundary within the water-carbon interrelationship and is a high-carbon and high-water reservoir. In this paper, the tropical
zone is categorized as a typical and specific boundary among the planetary boundaries. Here, the tropical zone is classified as the tropical zone boundary, which is
approaching the “beyond the zone of uncertainty (high risk)” category due to climate
change and anthropological impacts. Within the tropical zone boundary, tropical
peatlands, especially those on the fringes of islands in Southeast Asia, have been
strongly influenced by El Niño because they are high-carbon and high-water reservoir ecosystems (Tsuji et al. 2019). Tropical peatlands are key ecosystems within the
tropical zone boundary. As tropical peatlands are high-carbon and high-water
reservoir ecosystems that cover large areas and are affected by climate change,
tropical peatlands are one of the core ecosystems among the planetary boundaries;
therefore, tropical peatlands can be defined as the tropical peatland boundary.
Tropical peatlands have been degraded or destroyed by climate change impacts
and land-use change impacts that directly affect water conditions and decrease the
groundwater level (GWL) and soil moisture (Fig. 1.1). These water issues cause
carbon losses from tropical peatlands through (1) carbon emissions from peat
oxidized in fires and from microorganism degradation and (2) dissolved organic
matter loss through water drainage.
A developed tropical peatland is characterized with PB elements such as:
6
M. Osaki et al.
PB3: Land-use change (yellow)
PB4: Freshwater consumption (green)
PB5: Biogeochemical flows (nitrogen and phosphorus) (red)
PB6: Ocean acidification (green)
PB7: Atmospheric aerosol loading (not yet quantified)
PB8: Stratospheric ozone depletion (green)
PB9: Novel entities (not yet quantified).
Each color in parentheses shows the following:
Green: Below the boundary (safe),
Yellow: In zone of uncertainty (increasing risk) and
Red: Beyond the zone of uncertainty (high risk).
Climate change is one of the key elements of “planetary boundaries” (Rockstrom
et al. 2009), for which El Niño is an outstanding indicator of climate change. El Niño
seriously affects tropical zones (Hamada et al. 2002, 2012; Yamanaka 2016, 2020).
The annual terrestrial GPP (gross primary production) across latitudes (in 0.5
bands) is the highest in tropical zones regardless of the different models used for the
calculations (Beer et al. 2010). Tropical forests and savannas account for 60% of
terrestrial GPP (123 Æ 8 Pg C year
À1 ). The GPP over 40% of the vegetated land on
Earth is positively associated with precipitation. Additionally, Beer et al. (2010)
show high spatial correlation between GPP and precipitation, suggesting the existence of missing processes or feedback mechanisms that attenuate the response of
vegetation to climate. On the other hand, as the precipitation and cloud distribution
are the highest in tropical zones (Yamanaka 2016; Wang et al. 2019; Ramage 1968;
Worden et al. 2007), the highest precipitation rate should result in the highest GPP.
Thus, the tropical zone is one kind of boundary within the water-carbon interrelationship and is a high-carbon and high-water reservoir. In this paper, the tropical
zone is categorized as a typical and specific boundary among the planetary boundaries. Here, the tropical zone is classified as the tropical zone boundary, which is
approaching the “beyond the zone of uncertainty (high risk)” category due to climate
change and anthropological impacts. Within the tropical zone boundary, tropical
peatlands, especially those on the fringes of islands in Southeast Asia, have been
strongly influenced by El Niño because they are high-carbon and high-water reservoir ecosystems (Tsuji et al. 2019). Tropical peatlands are key ecosystems within the
tropical zone boundary. As tropical peatlands are high-carbon and high-water
reservoir ecosystems that cover large areas and are affected by climate change,
tropical peatlands are one of the core ecosystems among the planetary boundaries;
therefore, tropical peatlands can be defined as the tropical peatland boundary.
Tropical peatlands have been degraded or destroyed by climate change impacts
and land-use change impacts that directly affect water conditions and decrease the
groundwater level (GWL) and soil moisture (Fig. 1.1). These water issues cause
carbon losses from tropical peatlands through (1) carbon emissions from peat
oxidized in fires and from microorganism degradation and (2) dissolved organic
matter loss through water drainage.
A developed tropical peatland is characterized with PB elements such as:
6
M. Osaki et al.