Carbon stocks of intact mangroves and carbon emissions arising from their conversion in the Dominican Republic

Study Number

83

Author

J. Boone Kauffman, Chris Heider, Jennifer Norfolk, Frederick Payton

Abstract

Mangroves are recognized to possess a variety of ecosystem services including high rates of carbon sequestration and storage. Deforestation and conversion of these ecosystems continue to be high and have been predicted to result in significant carbon emissions to the atmosphere. Yet few studies have quantified the carbon stocks or losses associated with conversion of these ecosystems. In this study we quantified the ecosystem carbon stocks of three common mangrove types of the Caribbean as well as those of abandoned shrimp ponds in areas formerly occupied by mangrove—a common land-use conversion of mangroves throughout the world. In the mangroves of the Montecristi Province in Northwest Dominican Republic we found C stocks ranged from 706 to 1131 Mg/ha. The medium-statured mangroves (3–10 m in height) had the highest C stocks while the tall (>10 m) mangroves had the lowest ecosystem carbon storage. Carbon stocks of the low mangrove (shrub) type (<3 m) were relatively high due to the presence of carbon-rich soils as deep as 2 m. Carbon stocks of abandoned shrimp ponds were 95 Mg/ha or ~11% that of the mangroves. Using a stock-change approach, the potential emissions from the conversion of mangroves to shrimp ponds ranged from 2244 to 3799 Mg CO2e/ha (CO2 equivalents). This is among the largest measured C emissions from land use in the tropics. The 6260 ha of mangroves and converted mangroves in the Montecristi Province are estimated to contain 3 841 490 Mg of C. Mangroves represented 76% of this area but currently store 97% of the carbon in this coastal wetland (3 696 722 Mg C). Converted lands store only 4% of the total ecosystem C (144 778 Mg C) while they comprised 24% of the area. By these metrics the replacement of mangroves with shrimp and salt ponds has resulted in estimated emissions from this region totaling 3.8 million Mg CO2e or ~21% of the total C prior to conversion. Given the high C stocks of mangroves, the high emissions from their conversion, and the other important functions and services they provide, their inclusion in climate-change mitigation strategies is warranted.

Main Results and Conclusions

• Mangrove forests store an exceptionally high amount of carbon, regardless of the height of the trees that constitute the forest.
  • “The relatively high concentration of C throughout the profile of the mangroves resulted in high carbon stocks.” (523)
  • “The mean total ecosystem carbon stock of the Montecristi mangroves was 853 Mg/ha (Fig. 3).” (523)
  • “We estimated the total C stock of the Montecristi wetland is 3 841 490 Mg C (excluding both the unsampled C in mudflats and open water).” (524)
  • “Mangroves currently store a estimate 97% of the carbon of this area (3 696 722 Mg C).” (524)
• Carbon stocks of shrimp ponds that had been converted from mangrove forests were considerably less than the carbon stocks of intact mangrove forests. The conversion of mangrove forests to shrimp ponds has a negative impact on the ability of the soil in that region to store carbon.
  • “The C stocks of shrimp ponds were only about ~11% of that of the mangroves. This represents a potential loss of 661-1135 Mg C/ha when mangroves are converted to shrimp ponds.” (524)
  • “Converted lands were estimated to be 24% of the vegetated area (1516 ha) but stored only 4% of the total ecosystem C (144 768 Mg C).” (524)
  • “Assuming that these [shrimp ponds] were formerly mangrove, conversion resulted in large losses of C stocks.” (525)
• The reduction in carbon stocks by conversion of mangrove forests leads to carbon emissions. Emissions from land-use conversion of mangrove forests in the area were found to be five times those predicted from conversion of tropical evergreen to cattle pasture and over 11 times those predicted from conversion of dry forest to cattle pasture.
  • “estimate of 1 036 971 Mg C lost due to conversion of mangrove to cultivated salt ponds, shrimp ponds, and other uses…or a loss of 21% of the potential ecosystem carbon stocks of the Montecristi wetlands since conversion.” (524)
  • “the cumulative emissions from the 1516 ha that have been converted are 3.8 million Mg CO2e.” (525)
  • “The emissions arising from conversion of tropical evergreen and dry forest to pasture are about 20% and 9% of the predicted emissions arising from the conversion of mangrove to shrimp ponds, respectively.” (525)
  • “emissions from 1 ha of mangrove converted to shrimp ponds is equivalent to the emissions of about 5 ha of tropical evergreen conversion and 11.5 ha of tropical dry forest.” (525)
• Current estimates indicate that worldwide mangrove deforestation accounts for 10% of all emissions associated with forest conversion. The actual percentage is likely higher. This finding indicates that mangroves are a far more effective at storing carbon than other types of forests. Because of this role in storing carbon and their other functions in coastal environments, mangroves should be included in efforts to mitigate climate change.
  • “When converted, the C losses are high because large quantities of C formerly stored in suboxic soils are lost, resulting in potentially large greenhouse-gas emissions.” (526)
  • “Rates of deforestation of mangroves are among the highest of all ecosystems in the tropics (Polidoro et al. 2010).” (526)

Works Cited

Polidoro, B. A., K. E. Carpenter, L. Collins, N. C. Duke, A. M. Ellison, J. C. Ellison, E. J. Farnsworth, E. S. Fernando, K. Kathiresan, N. E. Koedam, S. R. Livingstone, T. Miyagi, G. E. Moore, V. N. Nam, J. E. Ong, J. H. Primavera, S. G. Salmo, III, J. C. Sanciangco, S. Sukardjo, Y. Wang, and J. W. H. Yong. 2010. The loss of species: Mangrove extinction risk and geographic areas of global concern. PLoS ONE 5(4):e10095. doi:10.1371/journal.pone.0010095.