14
2% that of tropical rainforests, the carbon storage rates of blue carbon ecosystems
and tropical rainforests are similar.
It is therefore apparent that the area of coastal macrophytes makes a large contribution to the reduction of greenhouse gases, like terrestrial forests. However, the
UNEP report also shows that coastal macrophytes are disappearing faster than tropical rainforests. The areas lost since the 1940s corresponds to about 35%, 35%, and
25% of the areas previously occupied by mangrove forests, seagrass beds, and saltmarshes, respectively. The decline of coastal macrophyte communities has continued. The recent estimated rate of decrease have been about 1.5 percent per year for
these coastal vegetation, meaning that 0.15–1.02 billion tons of carbon dioxide are
being released annually (Pendleton et al. 2012).
The areal extent of the blue carbon ecosystem along the Japanese coast has not
been an exception to this pattern; a significant decrease has occurred. In particular,
the areas occupied by saltmarshes and seagrass beds have decreased as a result of
coastal developments throughout Japan for the past 100 years. The only exceptions
to this pattern have been the mangrove forests in the Nansei Islands. The area of
freshwater and saltwater marshes was about 2100 km
2
(of which Hokkaido
accounted for 84%) in the 1910’s and 1920’s. That area had declined to only 820 km
2
(of which Hokkaido still accounted for 86%) in 1999 (Geospatial Information
Table 1.2 Comparison of amounts and rates of carbon storage between blue carbon ecosystems
and major ecosystems
Global area
(×10
3 km
2 )
Carbon storage
amount per area
(Carbon Mg /ha)
Carbon storage
rate per area
(Carbon g/m
2
/
year)
Annual carbon
storage amount
(Range) (Carbon Tg/
year)
Seagrass beds
177
140
101
18
Mangrove
forests
138
864
163
23
Saltmarshes
51
162
151
7.7
Peatlands
3341
1497
11
36
Tropical forests 19,623
238
4.0
79
Temperate
forests
10,400
196
5.1
53
Boreal forests
13,700
117
4.6
49
Tropical
savannah/
grasslands
15,000
187
Temperate
grasslands
9000
159
2.2
20
Shrublands
8500
122
Deserts
18,000
91
0.8
14
Tundra
8000
166
1.2
10
Cropland
14,000
150
Extreme
24,000
1
Dessert/rock/ice
Modified from Bridgham (2014)
M. Hori et al.
2% that of tropical rainforests, the carbon storage rates of blue carbon ecosystems
and tropical rainforests are similar.
It is therefore apparent that the area of coastal macrophytes makes a large contribution to the reduction of greenhouse gases, like terrestrial forests. However, the
UNEP report also shows that coastal macrophytes are disappearing faster than tropical rainforests. The areas lost since the 1940s corresponds to about 35%, 35%, and
25% of the areas previously occupied by mangrove forests, seagrass beds, and saltmarshes, respectively. The decline of coastal macrophyte communities has continued. The recent estimated rate of decrease have been about 1.5 percent per year for
these coastal vegetation, meaning that 0.15–1.02 billion tons of carbon dioxide are
being released annually (Pendleton et al. 2012).
The areal extent of the blue carbon ecosystem along the Japanese coast has not
been an exception to this pattern; a significant decrease has occurred. In particular,
the areas occupied by saltmarshes and seagrass beds have decreased as a result of
coastal developments throughout Japan for the past 100 years. The only exceptions
to this pattern have been the mangrove forests in the Nansei Islands. The area of
freshwater and saltwater marshes was about 2100 km
2
(of which Hokkaido
accounted for 84%) in the 1910’s and 1920’s. That area had declined to only 820 km
2
(of which Hokkaido still accounted for 86%) in 1999 (Geospatial Information
Table 1.2 Comparison of amounts and rates of carbon storage between blue carbon ecosystems
and major ecosystems
Global area
(×10
3 km
2 )
Carbon storage
amount per area
(Carbon Mg /ha)
Carbon storage
rate per area
(Carbon g/m
2
/
year)
Annual carbon
storage amount
(Range) (Carbon Tg/
year)
Seagrass beds
177
140
101
18
Mangrove
forests
138
864
163
23
Saltmarshes
51
162
151
7.7
Peatlands
3341
1497
11
36
Tropical forests 19,623
238
4.0
79
Temperate
forests
10,400
196
5.1
53
Boreal forests
13,700
117
4.6
49
Tropical
savannah/
grasslands
15,000
187
Temperate
grasslands
9000
159
2.2
20
Shrublands
8500
122
Deserts
18,000
91
0.8
14
Tundra
8000
166
1.2
10
Cropland
14,000
150
Extreme
24,000
1
Dessert/rock/ice
Modified from Bridgham (2014)
M. Hori et al.