85
annual growth increments of aboveground biomass range from 4 t ha
−1
year
−1
in an
Avicennia mangrove forest in Mexico (Day et al. 1996) to 26.7 t ha
−1
year
−1
in a
Rhizophora forest in Thailand (Christensen 1978). Although very little information
is available about annual belowground biomass increments in mangrove ecosystems, Ong et al. (1995) reported growth increments in a Rhizophora apiculata stand
in Malaysia of 0.08 t C ha
−1
year
−1
for leaves, 0.44 t C ha
−1
year
−1
for branches,
5.56 t C ha
−1
year
−1
for trunk, 0.64 t C ha
−1
year
−1
for (aerially exposed) stilt roots,
and 0.42 t C ha
−1
year
−1
for roots buried in the soil (total, 7.14 t C ha
−1
year
−1
).
Mangrove ecosystems typically include multiple waterways. The primary producers in these waterways include periphyton, benthic algae (microphytobenthos), and phytoplankton. Production of periphyton on mangrove aerial roots
ranges from 0.14 to 1.1 g C m
−2
day
−1
(Lugo et al. 1975; Hoffman and Dawes
1980). Benthic algal production was 0.11–0.18 g C m
−2
day
−1
in a forest in
Thailand, in which the production from trees was 1.90–2.75 g C m
−2
day
−1
(Kristensen et al. 1988); the production of benthic algae thus accounted for <10%
of the total plant production. The net primary productivity of phytoplankton in
most mangrove ecosystems is essentially nil, because very little light penetrates
into the turbid waters (Ong et al. 1984).
Figure 3.7 illustrates the food web in a mangrove ecosystem. The living parts of
primary producers are eaten by herbivores, including primary consumers such as
insects. These primary consumers extract energy from the organic materials that
they eat. Secondary consumers—carnivores—eat primary consumers and extract
energy from their biomass. These carnivores then pass on this energy to the next
trophic level, tertiary consumers, which are carnivores that feed only on secondary
consumers. The ecosystem also has a detrital chain, which starts with dead material
from the primary producers, namely plant litter such as leaves and woody tissues,
and dead roots. Organisms such as crabs, snails, and mudskippers are detritivores,
which extract energy from these dead organic materials and are subsequently eaten
by carnivores (the detrital food chain is describe in more detail in Sect. 3.5.2.1).
Although many leaves in a mangrove forest typically show insect damage, the
resulting plant production loss is not very high. Robertson and Duke (1987) reported
that direct grazing by herbivores accounted for a loss of only 0.3–3.5% of the total
expanded leaf area in a mangrove forest in Australia. However, the loss from grazing can differ substantially depending on what kinds of herbivores inhabit the forest.
For example, mangrove forests of Southeast Asia probably suffer a large biomass
loss from leaf-eating monkeys, which like to eat young buds of mangrove trees.
3.5.1.2 Biomass Stocks
Biomass in mangroves, as in upland forests, is estimated by measuring trunk diameter and height and other physical parameters and then substituting the measured
values into an allometric equation which relates these measurements to biomass
(Table 3.5). Many studies have estimated aboveground biomass in mangrove forests, but very few have estimated belowground biomass, probably because of the
3 Carbon Sequestration in Mangroves
annual growth increments of aboveground biomass range from 4 t ha
−1
year
−1
in an
Avicennia mangrove forest in Mexico (Day et al. 1996) to 26.7 t ha
−1
year
−1
in a
Rhizophora forest in Thailand (Christensen 1978). Although very little information
is available about annual belowground biomass increments in mangrove ecosystems, Ong et al. (1995) reported growth increments in a Rhizophora apiculata stand
in Malaysia of 0.08 t C ha
−1
year
−1
for leaves, 0.44 t C ha
−1
year
−1
for branches,
5.56 t C ha
−1
year
−1
for trunk, 0.64 t C ha
−1
year
−1
for (aerially exposed) stilt roots,
and 0.42 t C ha
−1
year
−1
for roots buried in the soil (total, 7.14 t C ha
−1
year
−1
).
Mangrove ecosystems typically include multiple waterways. The primary producers in these waterways include periphyton, benthic algae (microphytobenthos), and phytoplankton. Production of periphyton on mangrove aerial roots
ranges from 0.14 to 1.1 g C m
−2
day
−1
(Lugo et al. 1975; Hoffman and Dawes
1980). Benthic algal production was 0.11–0.18 g C m
−2
day
−1
in a forest in
Thailand, in which the production from trees was 1.90–2.75 g C m
−2
day
−1
(Kristensen et al. 1988); the production of benthic algae thus accounted for <10%
of the total plant production. The net primary productivity of phytoplankton in
most mangrove ecosystems is essentially nil, because very little light penetrates
into the turbid waters (Ong et al. 1984).
Figure 3.7 illustrates the food web in a mangrove ecosystem. The living parts of
primary producers are eaten by herbivores, including primary consumers such as
insects. These primary consumers extract energy from the organic materials that
they eat. Secondary consumers—carnivores—eat primary consumers and extract
energy from their biomass. These carnivores then pass on this energy to the next
trophic level, tertiary consumers, which are carnivores that feed only on secondary
consumers. The ecosystem also has a detrital chain, which starts with dead material
from the primary producers, namely plant litter such as leaves and woody tissues,
and dead roots. Organisms such as crabs, snails, and mudskippers are detritivores,
which extract energy from these dead organic materials and are subsequently eaten
by carnivores (the detrital food chain is describe in more detail in Sect. 3.5.2.1).
Although many leaves in a mangrove forest typically show insect damage, the
resulting plant production loss is not very high. Robertson and Duke (1987) reported
that direct grazing by herbivores accounted for a loss of only 0.3–3.5% of the total
expanded leaf area in a mangrove forest in Australia. However, the loss from grazing can differ substantially depending on what kinds of herbivores inhabit the forest.
For example, mangrove forests of Southeast Asia probably suffer a large biomass
loss from leaf-eating monkeys, which like to eat young buds of mangrove trees.
3.5.1.2 Biomass Stocks
Biomass in mangroves, as in upland forests, is estimated by measuring trunk diameter and height and other physical parameters and then substituting the measured
values into an allometric equation which relates these measurements to biomass
(Table 3.5). Many studies have estimated aboveground biomass in mangrove forests, but very few have estimated belowground biomass, probably because of the
3 Carbon Sequestration in Mangroves