Sri Lanka: Learning from Failure – Mixed Results of Post-tsunami Mangrove Restoration

Restoration site, where most of the mangroves have died. These seedlings were planted in water that was too deep, and in a site where mangroves didn’t grow historically (KAS Kodikara, 2013)


In 2004, the devastating Indian Ocean tsunami invigorated the Sri Lankan government and people to turn their attention to restoring the country’s mangrove stands to prevent such catastrophic damage from future disasters. It has an area of approximately square 65,610km with a coastline of about 1,620km on the Indian Ocean. Mangrove restoration projects were launched in Sri Lanka covering over 2,000 hectares. However, over 80% of these projects failed. Kondikara et al. 2017 conducted an assessment of the success of 23 mangrove restoration projects implemented following the 2004 tsunami. Their assessment consisted of an ecological (e.g. species planted), social (e.g. drivers of planting initiatives), and economic assessment. The lessons learned from both the failures and successes of mangrove restoration can be used to inform the design, coordination, and implementation of other mangrove restoration projects.

Quick Facts

Project Location:
Unnamed Road, Sri Lanka, 6.392515890835014, 81.08508762903523

Geographic Region:

Country or Territory:
Sri Lanka


Estuaries, Marshes & Mangroves

Area being restored:
2,000 hectares

Project Lead:
Sri Lankan Government

Organization Type:
Governmental Body

Project Partners:
NGOs (both local and international) foreign governments, and University partners


Project Stage:

Start Date:

End Date:

Primary Causes of Degradation

Fire & Weather Events, Fisheries & Aquaculture, Fragmentation

Degradation Description

Sri Lanka was severely affected by the 2004 tsunami including many of the mangrove stands. Prior to the tsunami, many mangroves and potential planting sites were impacted by resource extraction (firewood, timber) and shrimp farming. 

Defining the Reference Ecosystem

The reference ecosystem is primarily based on contemporary reference sites or existing analogues of the pre-degradation ecosystem.

Reference Ecosystem Description

Compared to other Southeast Asian countries, there has been considerable research on mangroves in Sri Lanka. This research provides a baseline for the reference ecosystem. 

The projects are situated in all four different climate zones, that is, wet, dry, intermediate, and arid zones. However, the proportion of sites was different in these four zones: 52% of the planted sites were situated in the dry and arid climatic zones, 30% in the wet zone, and the rest, that is, 18%, are in the intermediate zone.  5,009ha of mangrove cover is found in the dry and arid zones, 644ha in the intermediate zone, and 430ha in the wet zone. However, mangrove cover between 1983 and 2003 was reduced by about 2,450ha in the dry and arid zones. 

Survival rate of planted seedlings for at least 5 years was used as the indicator for success. Specifically, the survival of Rhizophora mucronata was assessed.  Attention was also paid to soil conditions and topographic position of the restored area. 


Project Goals

  1. Coastal protection against tsunami events.
  2. Mangrove regeneration


The project does not have a monitoring plan.


Many of the mangrove restoration projects were a collaboration between Sri Lankan government, foreign governments, and non-governmental organizations (NGOs). However, there was often a lack of proper coordination between each of these institutions. The key actors involved in planting initiatives can be broadly categorized as governmental or nongovernmental organizations (national and international). The governmental organizations include the Coastal Conservation Department, Regional Forest Departments, the University of Ruhuna, the National Aquatic Resources Research and Development Agency. IUCN and Mericarp are the international NGOs, while Galle project, Sewalanka, Turtle Conservation Project, Saviya Development Foundation, and Small Fishers Federation of Lanka are local NGOs. In addition, there were five unidentified internationally affiliated NGOs that have attempted mangrove restoration in Sri Lanka in the past decade.

Local coastal communities were tasked with the actual implementation of restoration work, but often were not educated about the technical requirements of this restoration work and had little oversight.

How this project eliminated existing threats to the ecosystem:
Local communities were not effectively involved in the implementation process and widespread political support and political cohesion between partners was not achieved.

How this project reinstated appropriate physical conditions (e.g. hydrology, substrate)",:
Since the Indian Ocean tsunami in 2004, approximately 1,000–1,200ha of mangroves have been planted. However, planting agencies did select sites based on soil/substrate composition, climate, or topography.

How this project achieved a desirable species composition:
Planting agencies did not survey which species occur naturally in the area nor did they use nearby natural forests as reference sites as recommended in restoration guides. 

Ecological Outcomes Achieved

Eliminate existing threats to the ecosystem:
Many of the restored sites experienced continual high level of disturbance following planting efforts. Such disturbance included cattle trampling and browsing. Political support for shrimp farming, which destroys mangrove habitat, is still widespread.

Reinstate appropriate physical conditions",:
The current total surviving planted area is only about 200–220ha of the original 1,000-2,000 hectares of restored mangrove. Soil pH for the study sites ranged from 7.1 to 5.8. The sites in the wet zone showed significantly lower pH values (p=0.0003; sig. level 0.001) as compared to the rest. SBD ranged from 1.22 to 1.89g/cm3. The bulk densities were significantly lower (p=0.03; sig. level 0.05) in the arid zone. Redox potential at 30 and 50cm ranged from +6 to−146mV and −43 to −171mV, respectively. Redox potential at 30cm was relatively higher in the intermediate and wet zones than in the dry and arid zones. Below a depth of 30cm, redox potential varied between −100 and −200mV. However, there was no significant difference of redox potential at 30 and 50cm between the different climate zones.

Achieve a desirable species composition:
The large majority of seedlings planted were of Rhizophora spp., that is, 97% of the total planted propagules and seedlings, rather than selecting and planting native mangrove species. Selecting inappropriate mangrove species for the area was a leading cause of restoration failure.

Reinstate structural diversity:
The average height of planted mangroves in Thambalangama, Rekawa, Galle, Negombo, Pambala, and Kalpitiya was found to be 4–6m in 8–10 years. However, stunted growth and crooked saplings were observed in the project sites situated in Panama, Panakala, and Halawa.

Recover ecosystem functionality:
Thirty-six (36) planting attempts out of 67 (54% of the total) showed no surviving plants. Two-thirds of these complete failures were recorded in the dry and arid zones. In total, for all the project sites, the level of survival (based on the dead/alive criterion) varied from 0 to 78%. Even after several planting attempts 40% of the sites had failed (9 out of 23 had no surviving plants). Further, the level of survival for 16 of the project sites was lower than 10%. Only three sites had a survival rate over 50%.

Reestablish external exchanges with the surrounding landscape:
The placement of plants at locations with inappropriate topography which subjects them to too short or too long periods of depth, duration, and frequency of inundation, either from local rainfall or local tides, or a combination of both, has been the key factor. In addition, crucial factors for planting success such as awareness of the history of the sites including species composition, hydrological requirements, optimum depth of substrate, and freshwater input were ignored in most of our study sites

Factors limiting recovery of the ecosystem:
There were multiple planting initiatives by different agencies within the same sites. Sixty-seven planting initiatives were recorded within these 23 sites. Many planting attempts could be observed in tsunami-affected areas Many failed mangrove restoration project sites could be observed in the tsunami-affected areas, while the most successful restoration sites were in areas less affected by the tsunami. Additionally, the restored sites were situated in a wide range of topographic positions. Some planting efforts were situated at the high intertidal area and even beyond, in abandoned swamps, and meadows, while some were in the low intertidal zone. Inappropriate topographic positioning such as this subjects mangrove seedlings to several stress factors and disturbances. Indications of stress factors and disturbances (drought, smothering, high irradiance, flooding, algal accumulation, infestation by barnacles, browsing, and cattle trampling) (Fig. 6) were observed in all restoration sites. Cattle trampling and browsing were ubiquitous. The occurrence of some types of stress factors and disturbances were related to the climate zone. For instance, mangrove seedlings/propagules planted in the low intertidal area were exposed to long-term submergence due to heavy rains in the wet zone while mangrove seedlings/propagules at the higher intertidal area suffered due to drought and high irradiance.

Socio-Economic & Community Outcomes Achieved

Has the project had any negative consequences for surrounding communities or given rise to new socio-economic or political challenges?:
The success of mangrove restoration are also critical from a financial and risk-assessment perspective as human lives may depend on the coastal protection claimed to be offered by these planting initiatives. Thus, when these projects fail, negative consequences include increased financial and risk for communities impacted by lack of coastal protection. No political support exists for mangrove planting while shrimp farming extends under political patronage.

Key Lessons Learned

  1. Mangrove restoration has multiple important benefits socioeconomically providing natural resources, preventing natural disaster damage, and ecologically. As such, mangrove restoration involves coordination between multiple institutions both foreign and local. These institutions must have structured coordination to ensure proper communication and each stage of the project. 
  2. It is important to involve local coastal communities in mangrove restoration efforts, but these communities must be provided adequate technical education and oversight about which species to plant in which areas. 
  3. Political support for restoration is critical. 
  4. Destructive activities such as fisheries and firewood collection must be effectively discouraged for restoration to be effective in the long term. 
  5. Restoration efforts are far less successful in dry and arid zones. 
  6. Mangrove restoration projects which are scientifically/technically guided are more successful than those guided primarily by donors. Technical guidance means recognizing basic principles like understanding autecology of mangrove species, and the normal hydrology of the sites, assessing appropriate modifications to hydrology, selecting restoration sites based on technical, political, social, and economic considerations, planting mangroves only as needed. 
  7. Ignorance of the major ecological drivers of mangrove health such as requirements for salinity, hydrology, and appropriate species composition were the main causes for mangrove restoration failure. 
  8. Inappropriate site selection is a major driver of mangrove restoration failure. 
  9. Lack of maintenance and monitoring also led to restoration failure, even in technically-guided restoration sites. 
  10.  Nation-wide evaluations of planting initiatives in the Southeast Asian region, where the bulk of global mangroves occur and where most mangrove restoration has taken place, are worthwhile for informing future restoration efforts and where to invest resources. 
  11. Planting mangroves in areas that have undergone major changes or in areas where mangroves were never reported should be preceded by a scientific assessment of whether or not mangroves can grow there.
  12.  Mangrove planting may not always be the best method for coastal protection. Scientific assessments should be conducted and sometimes other bioshield methods investigated. 

Long-Term Management

In an effort to deliver completed results quickly, many of the Sri Lankan restoration projects were implemented without investing much time in the planning and long-term monitoring. 

Ten sites demonstrated some monitoring efforts post-planting. Post-planting monitoring was identified as removing flotsam, debris, and attached barnacles, up-righting fallen seedlings/propagules, avoiding cattle trampling, and secured fencing and frequent site visits, and replacing dead seedlings/propagules. Survival rate was significantly correlated with post-planting care and soil parameters except soil pH.

Sources and Amounts of Funding

Over 13 million USD have been invested in these 23 restoration projects covering 2,000 hectares over the past decade (approximately $6,500 USD per hectare). 

Related Research

K. A. Sunanda Kodikara. 2017. Have mangrove restoration projects worked? An in-depth study in Sri Lanka, is published in Restoration Ecology (doi: 10.1111/rec.12492). This article assessed the 23 failed projects in Sri Lanka and assesses how to move forward with mangrove restoration in the future.

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