Opinion

Sinking Emissions: The Role of Tropical Mangrove Forests in Reducing C02

Returning from her fieldwork in Fiji, Honours Fellow Lauren MacRae reflects on the critical role of mangrove forests in combating the climate crisis.

Image via Shutterstock, ID: 297591356

Since the industrial revolution, atmospheric COconcentrations have increased from 280ppm to 407ppm, with this value predicted to continue rising.Australia is a key contributor to these statistics, emitting 15.4 metric tons of COper capita, one of the highest per capita emissions amongst developed countries.2

As a greenhouse gas, COabsorbs infrared radiation emitted from the Earth’s surface and thus results in a warming temperatures as the energy is unable to escape. Although surface temperature changes may be very small, even minor fluctuations can cause extreme climatic concequences.1

This week alone, headlines have chronicled the historic loss of Iceland’s Okjokull glacier, unprecedented heatwaves across Europe, and record-breaking flooding, wildfires and storms. As cities from Darwin to New York declare a ‘climate emergency’, it is becoming clear that carbon taxes and offsets are not enough. Parallel to the climate crisis coverage, rates of deforestation in the Amazon are surging, and coastal urbanisation throughout Asia is wiping out swathes of the world’s most valuable carbon sinks: mangroves.

Emissions Reductions through Forest Conservation

Whilst carbon dioxide emissions are commonly attributed to the burning of fossil fuels and coal-based electricity generation, other activities also result in emissions. Deforestation, particularly the deforestation of tropical regions, contributes to five billion metric tons of COper year globally.1 Forests are considered a “carbon sink”, where carbon can be stored for long time periods. Through photosynthesis, plants convert COto organic matter allowing them to grow. This organic matter can store carbon until it decomposes, at which point COis released back into the atmosphere in potentially significant quantities.

As a result, international carbon emissions schemes and management strategies have been developed to incentivise the protection of forests through financial payments. Schemes such as Reducing Emissions from Deforestations and Degradation (REDD) acknowledge the role of forest conservation in reducing COemissions, enabling global collaboration to achieve low cost emissions reductions.3

Offering payment as an incentive to conserve forest ecosystems sounds good on paper, however many challenges arise in its implementation.REDD relies on measuring the gains and losses of carbon stocks, but to do this appropriate baselines must be established. There are difficulties in monitoring, reporting and verifying carbon fluxes. Difficulties in financing the costs associated with these activities. Difficulties related to the displacement of deforestation. Difficulties in creating concrete definitions that have global applicability.

Despite this, it is evident that the responsible and sustainable management of forests is an essential component of carbon emission reductions. This management could be achieved through global management strategies, national policies or community-based management strategies.

The Role of Mangroves in Tropical Regions

In tropical countries, mangroves account for a significant portion of forest area and are an important ecosystem, offering ecosystem services essential for the maintenance of rural livelihoods. Mangroves have developed adaptations such as above ground roots that allow them to grow in highly saline intertidal regions. Many coastal communities directly rely on these ecosystem services as a source of fuel and construction wood, and as a habitat for fish and crab species. Furthermore, mangrove ecosystems enhance biophysical processes such as sediment accretion and wave attenuation that provide protection of coastal communities from sea level rise and storm events.5

Mangroves are capable of storing a far larger amount of carbon within a given area in comparison to other forest types, such as terrestrial forests.This carbon is stored either as the organic matter that makes up the tree (the above ground and below ground biomass) or as organic carbon in the surrounding soil. Carbon stored within the soil is a particularly important carbon pool, often exceeding the amount stored in the plant’s biomass (contributing between 49 and 98% of total carbon storage) and can remain stable for hundreds of years.7

Like other forests, mangroves also remove COfrom the atmosphere as they grow. Mangroves have a high photosynthetic capacity and primary production rate, meaning they grow faster than other forest types and thus can remove atmospheric COat a faster rate.8

Globally, mangroves are being deforested at an alarming rate. This destruction is often due to the conversion of mangrove forests for uses such as agriculture, development and aquaculture (particularly conversion to shrimp farms). As a result, it is estimated that mangroves account for 10% of emissions from deforestation globally, despite their relatively small land area.9

In addition to land clearing, mangrove forests can also be damaged and destroyed due to climatic stressors and extreme weather events such as tropical cyclones.

The potential of mangroves to significantly contribute to carbon management schemes is evident due to their high capacity for carbon storage and potential emissions associated with their deforestation. However, social studies that have considered the impacts of carbon management schemes on host communities however have found that these communities often benefit little or are detrimentally impacted by the schemes.3

Contrastingly, the protection of these ecosystems from existing pressures and threats may enable continued access to ecosystem services essential for local livelihoods. Moving forward, it is essential to incorporate local knowledge and land use into the development and implementation of any carbon management scheme – whether this is a part of international climate mitigation strategies or localised community-based management programs.

References
1. TAUSZ, M. AND MACKENZIE, R. 2017. Using forests to manage carbon: a heated debateThe Conversation. [Accessed 29 Jul. 2019].
2. THE WORLD BANK. 2019. CO2 emissions (metric tons per capita). [Accessed 29 Jul. 2019]. 
3. MATHUR, V. N., AFIONIS, S., PAAVOLA, J., DOUGILL, A. J. & STRINGER, L. C. 2014. Experiences of host communities with carbon market projects: towards multi-level climate justice. Climate Policy,14,42-62.
3. BAYRAK, M. & MARAFA, L. 2016. Ten years of REDD+: A critical review of the impact of REDD+ on forest-dependent communities. Sustainability,8,
4. LAU, W. 2013. Beyond carbon: conceptualizing payments for ecosystem services in blue forests on carbon and other marine and coastal ecosystem services. Ocean & Coastal Management, 83,5-14.
5. ALONGI, D. M. 2012. Carbon sequestration in mangrove forests. Carbon management, 3,313-322.
6. DONATO, D. C., KAUFFMAN, J. B., MURDIYARSO, D., KURNIANTO, S., STIDHAM, M. & KANNINEN, M. 2011. Mangroves among the most carbon-rich forests in the tropics.Nature Geoscience,4,
7. TANG, J. W., YE, S. F., CHEN, X. C., YANG, H. L., SUN, X. H., WANG, F. M., WEN, Q. & CHEN, S. B. 2018. Coastal blue carbon: Concept, study method, and the application to ecological restoration. Science China-Earth Sciences, 61,637-646.
8. HUTCHISON, J., MANICA, A., SWETNAM, R., BALMFORD, A. & SPALDING, M. 2014. Predicting global patterns in mangrove forest biomass. Conservation Letters, 7,233-240.


Lauren MacRae is an Honours Research Fellow with the Sydney Environment Institute. She has a Bachelor of Science majoring in Environmental Studies and Chemistry from the University of Sydney and is currently undertaking Honours with the school of Geosciences. Lauren’s research interests combine elements of physical and human geography to examine how climate change and management strategies impact Pacific Island nations, particularly Small Island Developing States.