Carbon pools and multiple benefits

Carbon sequestration

Carbon sequestration rates were based only on long-term permanent sample plot data from Cameroon and were found to vary with forest conditions (Table 10). Above ground components had proportionately higher sequestration rates (6.36 TonnesC/ha/yr) compared to below ground carbon pools. Undisturbed forests sequestered on average 16.52 TonnesC/ha/yr against 0.39 TonnesC/ ha/yr and 6.89 TonnesC/ha/yr by heavily and moderately exploited systems respectively. Mean sequestration rate for all forest conditions was 7.93 Tonnes C/ha/yr. These figures on carbon sequestration have implications for REDD+ strategies. They show that to maintain the highest carbon sequestration rates, then the greatest value comes from above ground biomass (trees) of undisturbed forests. These data show that there is a carbon incentive to conserve and sustainably manage undisturbed mangroves under REDD+ strategies, rather than to allow deforestation followed by replanting. The most vulnerable carbon pools following mangrove deforestation and degradation are the above ground carbon, as well as soil carbon from the top 30cm, where a large proportion of mangrove carbon lies (Donato et al., 2011). Estimating emissions from land-use change was conducted using uncertainty-propagation approach detailed in Donato et al., (2011). For the mangrove of Central Africa, a conservative low-end estimate of conversion impact, with 50% above ground biomass loss, 25% loss of soil carbon from the top 30cm, and no loss from deeper layers, in accordance with IPCC default values for areas without high levels of reclamation of mangrove habitat for other land-uses. Use of low-end conversion impact in the current study is justified by low-level reclamation of mangroves for aquaculture and agriculture in Central Africa. Carbon dioxide (greenhouse gas) emission potential

Using these conservative estimates, we estimate that 1,299 Tonnes of carbon dioxide would be released per ha of cleared pristine mangrove in Central Africa. This report estimates that 77,107 ha of mangrove were cleared in Central Africa between 2000 and 2010, equating to estimated emissions of 100,161,993 Tonnes of carbon dioxide. However, the net mangrove cover loss was only of 6,800 ha so a more conservative estimate would be of 8,833,200 Tonnes of carbon dioxide emitted between 2000 and 2010. Of course not all the carbon dioxide is released immediately, and these emissions occur over years or decades.

Table 10: Carbon sequestration in mangrove forests in Cameroon under different disturbance regimes

Biomass Carbon (MgC/ha/yr)

Exploitation regime

AGC

BGC

Total

Heavily exploited

0.19

0.20

0.39

Moderately exploited

5.21

1.68

6.89

Undisturbed

13.68

2.84

16.52

Average

6.36

1.57

7.93

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