94
storage (r
2
= 0.21 at estuarine sites, and r
2
= 0.50 at oceanic sites). Therefore, belowground necromass cannot be reliably estimated from aboveground data.
Atwood et al. (2017) analyzed mangrove soil carbon data from 48 countries and
found no difference in soil carbon storage per unit area between the northern and
southern hemispheres. They did find, however, that soil carbon storage (per unit
area) was 20% higher in mixed mangrove stands than it was in stands composed of
a single genus. They examined stands with various numbers of mangrove taxa,
ranging from single genus to as many as 7 genera, and reported that soil carbon storage per unit area was 70–90% higher in stands with 5 genera than it was in stands
with either more or fewer genera. Atwood et al. (2017) also found that forests composed of Laguncularia, Rhizophora, and Bruguiera had higher soil carbon storage
per unit area than those composed of other genera (in order of decreasing magnitude
of carbon storage, Xylocarpus, Lumnitzera, Avicennia, Kandelia, Ceriops, Heritiera,
Sonneratia, Excoecaria, Nypa, Conocarpus, and Aegiceras). Thus, estimated soil
carbon storage per unit area seems to vary greatly among mangrove forests (Jardine
and Siikamäki 2014; Atwood et al. 2017), probably because of differences in climate, species composition, hydrology, and topography.
From a global perspective, Jardine and Siikamäki (2014) estimated that the total
amount of carbon storage in mangrove soils is 5.00 Pg C, but Atwood et al. (2017)
estimated <2.6 Pg C. The large difference between these two estimates is due mainly
to the use of different mangrove areal distribution data. Jardine and Siikamäki
(2014) used the World Atlas of Mangroves (Spalding et al. 2010), whereas Atwood
et al. (2017) used data published by Hamilton and Casey (2016). Continuous monitoring and updating of global mangrove distribution data is clearly important. Both
of these estimates were made under the assumptions that carbon storage per unit
area is constant worldwide, and carbon is stored only to a soil depth of 100 cm. The
second assumption is made for practical reasons, because of the difficulty of measuring carbon storage in the entire soil profile (from the surface to underlying rock).
In fact, the amount of carbon stored at soil depths below 100 cm may be nonnegligible; thus, more carbon storage data in deep soil are needed to improve estimates of soil carbon storage in mangrove forests.
3.6 Conclusion
Donato et al. (2011) quantified whole-ecosystem carbon storage in 25 mangrove
forests in the Indo-West Pacific region (Kosrae Island in eastern Micronesia; Yap
and Palau islands in western Micronesia; Sulawesi, Java, and Borneo in Indonesia;
and the Sundarbans, in the Ganges–Brahmaputra delta in Bangladesh) and estimated that mangrove ecosystems in that region store an average of 1023 Mg C ha
−1
(Fig. 3.8). This number is extremely high compared with carbon storage in upland
forest ecosystems; boreal, temperate and tropical uplands (Fig. 3.8). Atwood et al.
(2017) estimated that whole-ecosystem carbon storage in mangrove ecosystems
was ~4.4 Pg C globally. Breithaupt et al. (2012) estimated the mean global
T. Inoue
storage (r
2
= 0.21 at estuarine sites, and r
2
= 0.50 at oceanic sites). Therefore, belowground necromass cannot be reliably estimated from aboveground data.
Atwood et al. (2017) analyzed mangrove soil carbon data from 48 countries and
found no difference in soil carbon storage per unit area between the northern and
southern hemispheres. They did find, however, that soil carbon storage (per unit
area) was 20% higher in mixed mangrove stands than it was in stands composed of
a single genus. They examined stands with various numbers of mangrove taxa,
ranging from single genus to as many as 7 genera, and reported that soil carbon storage per unit area was 70–90% higher in stands with 5 genera than it was in stands
with either more or fewer genera. Atwood et al. (2017) also found that forests composed of Laguncularia, Rhizophora, and Bruguiera had higher soil carbon storage
per unit area than those composed of other genera (in order of decreasing magnitude
of carbon storage, Xylocarpus, Lumnitzera, Avicennia, Kandelia, Ceriops, Heritiera,
Sonneratia, Excoecaria, Nypa, Conocarpus, and Aegiceras). Thus, estimated soil
carbon storage per unit area seems to vary greatly among mangrove forests (Jardine
and Siikamäki 2014; Atwood et al. 2017), probably because of differences in climate, species composition, hydrology, and topography.
From a global perspective, Jardine and Siikamäki (2014) estimated that the total
amount of carbon storage in mangrove soils is 5.00 Pg C, but Atwood et al. (2017)
estimated <2.6 Pg C. The large difference between these two estimates is due mainly
to the use of different mangrove areal distribution data. Jardine and Siikamäki
(2014) used the World Atlas of Mangroves (Spalding et al. 2010), whereas Atwood
et al. (2017) used data published by Hamilton and Casey (2016). Continuous monitoring and updating of global mangrove distribution data is clearly important. Both
of these estimates were made under the assumptions that carbon storage per unit
area is constant worldwide, and carbon is stored only to a soil depth of 100 cm. The
second assumption is made for practical reasons, because of the difficulty of measuring carbon storage in the entire soil profile (from the surface to underlying rock).
In fact, the amount of carbon stored at soil depths below 100 cm may be nonnegligible; thus, more carbon storage data in deep soil are needed to improve estimates of soil carbon storage in mangrove forests.
3.6 Conclusion
Donato et al. (2011) quantified whole-ecosystem carbon storage in 25 mangrove
forests in the Indo-West Pacific region (Kosrae Island in eastern Micronesia; Yap
and Palau islands in western Micronesia; Sulawesi, Java, and Borneo in Indonesia;
and the Sundarbans, in the Ganges–Brahmaputra delta in Bangladesh) and estimated that mangrove ecosystems in that region store an average of 1023 Mg C ha
−1
(Fig. 3.8). This number is extremely high compared with carbon storage in upland
forest ecosystems; boreal, temperate and tropical uplands (Fig. 3.8). Atwood et al.
(2017) estimated that whole-ecosystem carbon storage in mangrove ecosystems
was ~4.4 Pg C globally. Breithaupt et al. (2012) estimated the mean global
T. Inoue