To replant or not to replant natural barriers? Perhaps that is the wrong question

Contributed by Edward B. Barbier, Department of Economics & Finance, University of Wyoming

In a recent editorial in the New York Times (“False Hopes and Natural Disasters”, December 26, 2006), Andrew Baird has criticized Bill Clinton in his role as special envoy for UN tsunami recovery for endorsing publicly a $62 million program for preserving mangroves and coastal reefs as “natural barriers” to future tsunamis in 12 Indian Ocean countries. The program would expand substantially current programs in the region funded by governments and non-governmental organizations (NGOs) that are attempting to replant and rehabilitate mangrove ecosystems that have been severely degraded and even destroyed.

Baird’s argument is straightforward. He states that “there have been few scientific studies about the protective role of coastal vegetation.” What is more, he suggests that many post-tsunami assessments of “the level of protection offered by greenbelts has been exaggerated”. Assessments that Baird, his colleagues and other scientists have conducted have indicated that “neither reefs nor coastal forest reduced the damage caused by the tsunami.” Baird’s conclusion: replanting mangroves as “natural barriers” is misplaced; “if the aim is to protect people from tsunamis, the science indicates that money would better be spent on early warning systems, education and evacuation planning.”

I have some sympathy for Baird’s criticism of recent calls for widespread mangrove replanting “in the wake” of the December 2004 Indian Ocean tsunami. In September 2005 I had an opportunity to discuss such replanting programs with a member of a well-known international NGO, which was actively advocating mangrove replanting in Asia. I suggested to the NGO employee, who has a PhD in the biological sciences, that we need urgently to improve our ecological and economic assessments of the coastal protection value provided by replanted and restored mangrove ecosystems in order to ensure the success of the proposed costly investments in these “natural barriers”. The NGO person replied that such assessments were unnecessary. As a result of the 2004 tsunami, governments of Indian Ocean countries and the wider international community were now convinced of the need to replant mangroves as “natural barriers”, and plans to fund large-scale rehabilitation programs were already under way. In other words, there is no need for new scientific and economic studies, as we have already achieved the desired policy objective of convincing decisions-makers to invest in replanting and rehabilitating mangrove ecosystems in the Indian Ocean.

However, lost in this debate over whether or not to replant mangroves as natural storm barriers are three fundamental questions:

  • Why has widespread mangrove deforestation been occurring in Asia, and indeed globally, in recent decades?
  • Has this widespread loss of mangroves increased the vulnerability of coastal populations to economically damaging storm events, not just the occasional “big” tsunamis but the more frequent storm surges, typhoon and other tropical wind storms, and coastal floods that occur?
  • Are current institutions and incentives adequate for, first, encouraging local coastal communities to participate in mangrove replanting schemes, and second, to allow these communities a stake in the long-term management of the rehabilitated forests?

Mangrove forests are among the most threatened global ecosystems, especially in Asia. At least 35% of global mangrove area has been lost in the past two decades, and in Asia, 36% of mangrove area has been deforested, at the rate of 1.52% per year (Valiela et al. 2001). Although many factors are behind global mangrove deforestation, a major cause is aquaculture expansion in coastal areas, especially the establishment of shrimp farms (Barbier and Cox 2003). Aquaculture accounts for 52% of mangrove loss globally, with shrimp farming alone accounting for 38% of mangrove deforestation; in Asia, aquaculture contributes 58% to mangrove loss with shrimp farming accounting for 41% of total deforestation (see Valiela et al. 2001, Table 3). Forest use, mainly from industrial lumber and woodchip operations, causes 26% of mangrove loss globally and 16% in Asia, freshwater diversion accounts for 11% of loss globally and 14% in Asia, and reclamation of land for other uses causes 5% of loss globally and 7% in Asia. The remaining sources of mangrove deforestation consist of herbicide impacts, agriculture, salt ponds and other coastal developments, including resorts and tourism.

A stark reality is that many of these coastal developments causing mangrove loss rarely benefit local coastal communities. Traditional uses of the mangroves by these communities involve harvesting fish, wood products, honey and even medicines from the mangrove forests and swamps and fishing in the nearby coastal waters stocked by fish that depend on the mangroves for breeding grounds and nurseries. In contrast, commercial shrimp farming and aquaculture, logging operations, salt ponds, large-scale agricultural developments and resort hotels are usually owned and financed by outside investors who profit handsomely from these developments. Not only are local coastal people largely excluded from sharing these lucrative financial rewards, they hardly benefit at all, except perhaps for the lucky few who find employment as low-skill labor in these coastal development activities. Meanwhile, the traditional livelihoods of whole communities are often laid to waste along with the mangroves that support these livelihoods.

As we shall discuss presently, the question of “who gains” and “who loses” from mangrove deforestation turns out also to be an important consideration when addressing the social and economic feasibility of widespread mangrove replanting schemes in coastal areas.

The second question concerning the coastal protection service of mangroves gets to the heart of Baird’s criticism. There is, in fact, a very worrisome aspect to Baird’s argument. Readers of his editorial could infer that, if the main reason for replanting mangroves as “natural barriers” is to provide coastal populations protection again future “big tsunamis” such as the massive December 2004 storm event, then why replant or preserve mangroves at all if they offer little protection against such horrendously damaging events?The problem with such an inference is that it is highly faulty inductive reasoning, which to be fair to Baird I do not think he intended.

Baird actually acknowledges in his editorial that he considers tsunami to be a special case: “Mangroves forests are, to be fair, very effective at dissipating the energy of storm waves, but a tsunami is a very different beast….coastal forests at some point do begin to reduce tsunami damage, but we can’t expect them to offer meaningful protection against the sheer amount of energy involved in a tsunami.”

But does this mean that mangrove ecosystems offer little or no coastal storm protection at all? My own reading of the scientific literature and investigation into the storm protection value of mangroves in Thailand suggests that this is not the case (Barbier 2007).

First, as Baird admits, there is evidence in the literature that healthy mangrove forests can attenuate waves and buffer wind storms (Dahdouh-Guebas et al. 2005; Danielsen et al. 2005; Massel et al. 1999; Mazda et al. 1997; Wolanski 2007).

Second, tropical coasts are battered frequently by other storm events, not just massive tsunamis. This is illustrated in the figure below for Thailand.


Coastal natural disasters in Thailand, 1975-2004

Over 1975-2004, coastal natural disasters included wave/surge (tsunami and tidal wave), wind storm (cyclone/typhoon and tropical storm) and flood (significant rise of water level in coastal region. In order for EM-DAT (2005) to record an event as a disaster, at least one or more of the following criteria must be fulfilled: 10 or more people reported killed; 100 people reported affected; declaration of a state of emergency; call for international assistance.Â

Source: Barbier (2007); the original data source is EM-DAT(2005).EM-DAT: The OFDA/CRED International Disaster Database. – Université Catholique de Louvain, Brussels,Belgium.

The above figure shows that a variety of damaging coastal storm events occur frequently in Thailand, and that the incidence events (the number annually) has increased in recent years.

The economic damage per event (in real or constant US dollars) is also revealing, as the next figure shows.


Real damages per coastal natural disaster in Thailand, 1975-2004

The EM-DAT (2005) estimate of the economic impact of a disaster usually consists of direct (e.g. damage to infrastructure, crops, housing) and indirect (e.g. loss of revenues, unemployment, market destabilisation) consequences on the local economy. However, the estimate of “zero” economic damages may indicate that no economic damages were recorded for an event. The estimates of economic damages are in thousands of US$ and converted to 1996 prices using Thailand’s GDP deflator.

Source: Barbier (2007); the original data source is EM-DAT(2005).EM-DAT: The OFDA/CRED International Disaster Database. РUniversit̩ Catholique de Louvain, Brussels,Belgium.

The above figure plots the damages per coastal natural disaster in Thailand for 1975-2004. The 2004 Indian Ocean tsunami with estimated damages of US$240 million (1996 prices) was not the most damaging event to occur in Thailand. In fact, many other events, especially during the late 1980s to mid 1990s, were more damaging in real economic terms than the big tsunami.

Over the same time period, 1975-2004, extensive mangrove deforestation occurred in Thailand. This is illustrated in the following figure.

Mangrove area (km2) in Thailand, 1961-2004

FAO estimates from FAO (2003). 2000 and 2004 data are estimated from 1990-2000 annual average mangrove loss of 18.0 km2. Thailand estimates from various Royal Thailand Forestry Department sources reported in Aksornkoae and Tokrisna (2004). 2000 and 2004 data are estimated from 1993-1996 annual average mangrove loss of 3.44 km2

Source:Â Barbier (2007).

The above figure shows two long-run trend estimates of mangrove area in Thailand. Both trends show continuing mangrove loss, albeit at different rates. More importantly, over the past two decades the rise in the number and frequency of coastal natural disasters in Thailand and the simultaneous rapid decline in coastal mangrove systems over the same period is likely to be more than a coincidence. This suggests an important hypothesis worth examining: Did the widespread loss of mangroves in coastal areas of Thailand increase the vulnerability of these areas to more incidences of economically damaging natural disasters?

I tested this hypothesis recently; details can be found in Barbier (2007). The analysis for Thailand over 1979-96 and across 21 coastal provinces shows that a one-km2 decline in mangrove area increases the expected number of disasters by 0.36%. This relationship was statistically significant, and suggests that we cannot reject the hypothesis of correlation between mangrove deforestation and the incidence of damages from coastal storms in Thailand over 1979-96.

Based on this analysis, I was also able to calculate the resulting economic impacts associated with changes in forest area, both for 1979-96 and for the subsequent period 1996-2004. Over 1979-1996, the estimated real economic damages per coastal event per year in Thailand averaged around US$189.9 million (1996 prices). For this period, the marginal effect of a one-km2 loss of mangrove area is an increase in expected storm damages of about US$585,000 per km2. Over 1996-2004, the estimated real economic damages per coastal event per year in Thailand averaged around US$61.0 million (1996 prices). For this period, the marginal effect of a one-km2 loss of mangrove area is an increase in expected storm damages of about US$187,898 per km2.

In sum, consistent with most of the prevailing ecological literature on the coastal protection service of mangrove forests, the Thailand study shows that widespread deforestation over a significant period of time will increase the vulnerability of coastal areas to a variety of economically damaging storm events.

The final question I mention above raises concerns about the institutions and incentives in many coastal areas. In other words, even if we think that current calls to expand mangrove replanting and rehabilitation in Asia for coastal protection are worthwhile, will such schemes succeed?

In an article in Frontiers in Ecology and the Environment, I addressed this question also (Barbier 2006). I made the following points:

  • Although the post-tsunami change in attitude towards mangroves in the region is welcomed, focusing solely on replanting projects is not sufficient to reverse the decades-long decline in mangrove forests in the region.
  • Unless local coastal communities have more of a say in the control, use and protection of mangroves, current and future restoration projects will fail to have any lasting results.
  • Instead, a new institutional and policy framework that involves local communities more directly in coastal mangrove management could make a difference to the sustainability of mangrove rehabilitation projects in the Indian Ocean region, and may improve community participation in these projects.

For example, a new institutional framework for coastal mangrove management in Thailand and other Indian Ocean countries that could make a difference to coastal communities, including their willingness to restore and protect local mangroves, might contain the following features (Barbier and Sathirathai 2004). First, remaining mangrove areas should be designated into conservation (i.e. preservation) and economic zones. Shrimp farming and other extractive commercial uses (e.g., wood concessions) should be restricted to the economic zones only. However, local communities who depend on the collection of forest and fishery products from mangrove forests should be allowed access to both zones, as long as such harvesting activities are conducted on a sustainable basis. Second, the establishment of community mangrove forests should also occur in both the economic and conservation zones. However, the decision to allow such local management efforts should be based on the capability of communities to effectively enforce their local rules and manage the forest to prevent over-utilization, degradation and conversion to other land uses. Moreover, such community rights should not involve full ownership of the forest but be in the form of user rights. Third, the community mangrove forests should be co-managed by the government and local communities. Such effective co-management will require the active participation of existing coastal community organizations, and will allow the representatives of such organizations to have the right to express opinions and make decisions regarding the management plan and regulations related to the utilization of mangrove resources. Finally, the government must provide technical, educational and financial support for the local community organizations participating in managing the mangrove forests. For example, if only user rights (but not full ownership rights) are granted to local communities, then the latter’s access to formal credit markets for initiatives such as investment in mangrove conservation and replanting may be restricted. The government may need to provide special lines of credit to support such community-based activities.

However, establishing an improved institutional framework is a necessary but not sufficient step in controlling excessive shrimp farm expansion and subsequent mangrove loss. Reforms are needed to reduce the current perverse incentives for excessive mangrove conversion for shrimp farming. These include eliminating preferential subsidies for the inputs, such as larvae, chemicals and machinery, used in shrimp farming, ending preferential commercial loans for clearing land and establishing shrimp ponds, employing land auctions and concession fees for the establishment of new farms in the “economic zones” of coastal areas, and finally, charging replanting fees for farms that convert mangroves. Reducing the other environmental impacts of shrimp farming in Thailand and other Asian countries is also important, notably problems of water pollution, the depletion of wild fish stocks for feed and disease outbreaks within ponds. Improving the sustainability of shrimp aquaculture, as well as controlling the excessive mangrove deforestation caused by the industry, are both critical to the ensuring participation of local coastal communities in mangrove replanting efforts as well as their cooperation in long-run management of forests.

To conclude, a narrow focus on whether to replant or not to replant “in the wake” of the December 2004 tsunami fails to address the wider social, ecological and economic issues of mangrove management in the region. A successful strategy for mangrove rehabilitation, restoration and conservation in Asia needs to look beyond an overly simplified replanting debate.

Aksornkoae S and Tokrisna, R. 2004. Overview of shrimp farming and mangrove loss in Thailand. In: Barbier EB and Sathirathai S (Eds). Shrimp Farming and Mangrove Loss in Thailand. London: Edward Elgar.

Barbier, EB. 2006. “Natural barriers to natural disasters: replanting mangroves after the tsunami.” Frontiers in Ecology and the Environment 4(3):124-131.

Barbier, EB. 2007. Valuing ecosystem services as productive inputs. Economic Policy, January, 177-229.

Barbier EB and Cox M. 2003. Does economic development lead to mangrove loss? A cross-country analysis. Contemporary Economic Policy 21(4):418-432.

Barbier EB and Sathirathai S (Eds). 2004. Shrimp Farming and Mangrove Loss in Thailand. London: Edward Elgar.

Dahdouh-Guebas F, Jayatissa LP, Di Nitto D, et al. 2005. How effective were mangroves as a defence against the recent tsunami? Current Biology 15(12):443-447.

Danielsen F, Sørensen MK, Olwig MF, et al. 2005. The Asian tsunami: a protective role for coastal vegetation. Science 310:643.

FAO (UN Forest and Agricultural Organization). 2003. Satus and trends in mangrove area extent worldwide. By Wilkie, M.L. and Fortuna, S. Forest Resources Assessment Working Paper No. 63. Forest Resources Division, FAO, Rome.

Massel SR, Furukawa K and Brinkman RM. 1999. Surface wave propagation in mangrove forests. Fluid Dynamics Research 24:219-249.

Mazda Y, Wolanski E, King E, et al. 1997. Drag force due to vegetation in mangrove swamps. Mangroves and Salt Marshes 1:193-199.

Valiela I, Bowen JL and York JK. 2001. Mangrove forests: one of the world’s threatened major tropical environments. BioScience 51(10):807-815.

Wolanski, Eric. 2007. Protective functions of coastal forests and trees against natural hazards.” Food and Agricultural Organization (FAO) of the United Nations, Rome, forthcoming.