Mangrove Restoration: ‘To plant or not to plant?’
Mangrove forests are under threat from many development pressures: overharvesting, pollution, conversion for agriculture, aquaculture or urbanization, oil and gas industry and development of infrastructure. In many parts of the world mangroves have been lost, along with their valuable services. Generally speaking it is more cost-effective to prevent mangrove loss than to lose and restore them, but this is not always an option. Consequently, mangrove restoration is needed in many degraded areas across the world and if done properly, it will enhance coastal safety, fisheries, aquaculture and carbon sequestration.
After the 2004 Indian Ocean tsunami, the importance of mangroves became widely recognized. Since then, mangrove planting has become very popular, with governments, NGOs, private sector, students, religious leaders and newly-weds planting mangroves or raising funds for others to plant. Across the globe hundreds of thousands of hectares of mangroves have been actively planted. Unfortunately, the majority of planting efforts fail to effectively restore functional mangrove forests and we can learn from these experiences.
A more effective approach is to create the right conditions for mangroves to grow back naturally. Mangroves restored in this way generally survive and function better.
This leaflet* aims to contribute to best practice by exploring the question that everyone involved in mangrove restoration should ask: ‘To plant or not to plant?’
*Download the full publication from the right-hand column. Also available in Bahassa Indonesia – download available from the Further Resources section.
- The world needs mangroves, but in many parts of the world they have been lost or degraded, along with their valuable services like coastal protection or fisheries enhancement. Restoration is necessary in many places.
- Mangrove planting is hugely popular, but the majority of planting efforts fail to restore functional mangrove forests and we can learn from these experiences.
- Successful restoration results in the establishment of a sizeable, diverse, functional and self-sustaining mangrove forest that offers benefits for nature and people.
- When the enabling biophysical and socioeconomic conditions are put back in place applying Ecological Mangrove Restoration principles, nature will do the rest. When that happens, species to site matching is optimal, resulting in better survival, faster growth and a more diverse and resilient mangrove forest.
- In some cases, planting can assist or enrich the natural regeneration process. However, non-mangrove habitat and areas showing natural mangrove recruitment need to be avoided.
Recurring factors for failure mangrove planting
Recurring factors for failure include:
- Planting in areas where socio-economic conditions are not right, because the local community is not involved, does not support the idea of conservation or because alternative livelihoods are lacking. For example when the community depends on aquaculture, so that mangroves are quickly reconverted to fish or shrimp ponds.
- Mono-species planting, leading to non-functional mangroves, with limited benefits and low resilience.
- Planting the wrong species in the wrong places, with mortality or slow growth as a result. For example, planting in areas that are under water for too many hours a day, or in areas too high up the intertidal range. Planting in places that are too exposed to waves and erosion or that do not have proper soil or water quality.
- Planting in places where the recovered mangrove would block sediment and water flows thus hampering recovery at a larger scale.
- Planting in areas where the original cause of loss (for example altered water flow) has not changed.
- Planting in places where mangroves are settling naturally, causing damage to the naturally regenerating mangroves and thus disturbing and slowing down natural recovery.
- Planting in areas that were not previously covered by mangroves, such as open intertidal mudflats or seagrass beds or sandy beaches, which causes damage to such valuable habitats
What is successful mangrove restoration
The success of mangrove restoration is typically and pragmatically defined by the number of seedlings that have been planted and sometimes by the survival rate after a short period of time. However, many examples exist of planting efforts that demonstrate high survival initially but show high mortality in the longer run when monitoring has ended. Some efforts yield stunted single species stands, growing at unnatural densities. Such ‘mangroves’ do not offer the coastal protection, fisheries enhancement or other benefits aimed for.
Instead, successful restoration needs to result in the establishment of a sizeable, diverse, functional and self-sustaining mangrove forest that does offer such benefits. With this in mind, it would be much better to measure success against the extent to which desired benefits for nature and people return and remain in place. There are many ways to do this, typically involving the assessment of diversity and abundance, vegetation structure and ecological processes in at least two reference sites to capture variation.
Principles for successful mangrove restoration
To channel the overwhelming enthusiasm for mangrove restoration to those interventions that are most effective, the following two principles are of key importance:
- Ensure biophysical conditions are appropriate for mangrove recovery: Mangroves may have been lost or degraded through conversion for other land uses, or as a result of changes in freshwater supply, loss of sediments or other causes. These in turn might be linked to local infrastructure developments and engineering works along coasts and rivers further away. Consequently, mangroves may no longer be able to thrive where they used to. Regeneration of a healthy mangrove forest can only happen if the enabling biophysical conditions for mangrove growth are put back in place. This can be hard – but very rewarding – work. In former aquaculture land, ground-levelling and restoration of hydrological flows is needed. This can be done by strategically breaching of pond bunds and restoring old creek systems. On rapidly eroding muddy coasts in Indonesia, Vietnam and Suriname, permeable structures are being applied to reduce wave impact, trap sediment and then allow natural mangrove recovery.
- Ensure that socio-economic conditions allow mangrove recovery: If mangroves have been removed by people this could easily happen again. The socio-economic root causes need to be addressed to prevent that. Where possible, economic activities need to be developed that sustainably benefit from the restored mangrove values, thereby strengthening the business case for restoration. Land ownership and use rights need to be established, and there must be both a desire for recovery and a possibility for management. Successful projects empower communities, engage local government and ensure that local actions are strengthened by policies and planning
These two principles are the cornerstone of the so‑called Ecological Mangrove Restoration approach. This approach has a sound scientific basis. Strictly speaking, the term ‘restoration’ is reserved for the re‑establishment of the pre-existing ecosystem; while ‘rehabilitation’ refers to recovery of ecosystem functions and processes without necessarily re-establishing the pre-disturbance condition. Note that the interventions involved in Ecological Mangrove Restoration are very different from restoration by planting only, and should be part of a coordinated programme involving experts of various disciplines – e.g. ecology, hydrology, coastal dynamics, sociology – as well as multiple stakeholders.
So, when to plant and when not to plant?
Ecological Mangrove Restoration relies on natural regeneration once biophysical conditions are restored, and planting is in most cases not needed. Yet, there are occasions when planting may still be useful. Sometimes planting is inevitable due to existing commitments or its current popularity with stakeholders. In those cases, planting efforts need to be channelled such that efforts are useful and do not result in failure or even damage to the environment. At the same time capacity building around Ecological Mangrove Restoration is required.
Planting might be valuable under the following conditions:
- Planting or sowing may be required when natural supplies of seeds and propagules are limited due to lack of nearby ‘parent trees’ or lack of hydrological connection to these trees (inhibiting dispersal of seeds and propagules). This is often the case along coastlines that suffered widespread mangrove degradation.
- Planting may also be done to re-introduce specific valuable species that have been lost from an area, so‑called ‘enrichment planting’.
- Planting can also be valuable for educational or cultural purposes. As a symbol of life, planting a tree can create lasting commitment and ownership amongst all those involved.
- In severely eroding areas, mangrove planting on remaining bunds can offer short-term relief by delaying erosion of those bunds.
- In cases were planting is deemed necessary, appropriate species to site matching is vital. Non‑mangrove habitat and areas showing natural mangrove recruitment need to be avoided at all times.
Mangrove planting can of course also play a role even if ecosystem restoration is not the primary goal. For example, planting to provide a sustainable wood/timber source. Also, mangroves are often planted in combination with aquaculture systems (silvofisheries), to introduce additional benefits in the system. The rows of mangrove trees that are planted along aquaculture pond bunds won’t produce a ‘real’ mangrove forest, but may provide important benefits at the local scale like stabilisation of bunds, brushwood, fodder production and shade.
Communities may be used to the income they earn from nursery management and planting. A lot of their pride and ownership might be connected to the planting efforts. Ecological Mangrove Restoration needs to find alternative ways to practically engage the local community. For example in construction of permeable structures to trap sediment, breaching of bunds, sowing, monitoring and safeguarding the restored mangrove. Simultaneously sustainable livelihoods need to be developed to take the pressure off the recovered mangroves.
This leaflet was made possible by Waterloo Foundation, the Dutch Sustainable Water Fund and Otter Foundation and developed by Ecoshape, Wetlands International, the Ministry of Marine Affairs and Fisheries (MMAF), the Ministry of Public Work and Human Settlement (PU), Witteveen + Bos, Deltares, Wageningen University & Research Centre, and Blue Forests.
Wetlands International (2016) Mangrove restoration: to plant or not to plant? Wetlands International: Wageningen, The Netherlands