Ecological Mangrove Restoration Techniques
- field experience from southeast coast of India
Dr.V.Balaji, M.Sc., M.Phil., Ph.D.,
Director, OMCAR Foundation
According to (Lewis and Marshall 1997), there are five critical steps are necessary to achieve successful mangrove restoration:
1. Understand the autecology (individual species ecology) of the mangrove species at the site;in particular the patterns of reproduction, propagule distribution, and successful seedling establishment.
2. Understand the normal hydrologic patterns that control the distribution and successful establishment and growth of targeted mangrove species.
3. Assess modifications of the original mangrove environment that currently prevent natural secondary succession (recovery after damage).
4. Design the restoration program to restore appropriate hydrology and, if possible, utilize natural volunteer mangrove propagule recruitment for plant establishment.
5. Only utilize actual planting of propagules, collected seedlings, or cultivated seedlings after determining (through steps a-d) that natural recruitment will not provide the quantity of successfully established seedlings, rate of stabilization, or rate of growth of saplings established as objectives for the restoration project.
Ecological Mangrove Restoration is a slower process but has a much better rate of success, while the mangrove gardening may be faster in the suitable conditions, but creating a plantation is not the same as a biodiverse natural mangrove forest.
During my visit to Philippines, I went to mangrove restoration sites in some islands. The local people informed that restored mangroves were severaly damaged by previous year cyclone, while natural mangroves were less damaged.
The restored mangroves were planted in a row with equal distance by using same species. The distance between the adult trees was too close to each other, so they tended to grow more height to get sun light. It leads to weaker stem, unusual straight trees, like a commercial forestry. The forest has also had no associated flora, when compared to neighboring natural mangroves.
Hence, mangrove gardening (refers to growing a particular desired species of plant by artificially planting them in rows with equal distance along the canals or mudflats or degraded natural mangrove sites) is a failure model. It cannot effectively protect against natural disasters like natural mangroves and cannot restore natural biodiversity of mangrove ecosystem. See below Pictures 1 and 2 of a mangrove garden, which I took from Philippines in 2009.
Picture 1: Shows the weaker mangrove trees of mangrove gardening, which can not withstand natural disasters like natural mangroves.
Picture 2: Dr.V.Balaji is standing on a board walk laid in mangrove garden area in Philippines. See the damaged mangroves on the left side due to cylone. Look at the far distance in back side, where natural mangroves are denser and shorter.
Fact 2: Restoration of existing degraded mangroves is more important than planting new mangroves.
Generally, a first thought come to our mind about mangrove restoration is raising mangrove nursery and planting mangrove seedling in coast. In reality, there are several facts to be considered before we go into mangrove planting.
a) As mentioned in EMR techniques, we need to find the reason for existing mangrove degradation in the project site.
b) Discuss with local community to know their interest in mangrove restoration and explain how it would benefit them both economically and ecologically. Note that failure to get community interest in the project will not lead to a successful project impacts.
c) Develop a community based work plan to remove the threats to natural mangroves.
c) Restore natural water circulatory systems.
d) Restore natural seed sources (if the threats to natural adult mangrove trees removed, then it will be very easy to get enough seeds/seedlings)
e) As mentioned in EMR techniques, go for nursery raising and plantation if it is necessary. However, in developing countries mangrove nursery plays an important role to bind community participation in mangrove restoration activities such as backyard nursery.
Click below link to see how a natural degraded growing back faster, when compared to planted mangrove seedling in few years. These time lapse photos were taken by us in one of our mangrove restoration sites in Keezhathoddam village, Tamil Nadu, India. Run the slide show on both directions to see the growth of mangroves with years.
In the beginning of the above project, we restored natural water ways, which facilitated free tidal water flow between natural mangroves and the estuary. We connected the abandoned fish bone canals with natural water ways to make a water circulation. At the same time, we involved local community to raise mangrove seedlings and planted them in canals. The canal mangroves are growing now, however the mangrove seedlings grown on both side of the fish bone system are extending their roots. So, the mangroves themselves started to struggle for getting free tidal flow, which is slowed by their roots. When compared to mangrove seedlings in the mouth of fish bone canals, the seedlings planted in the back side of fish bone systems now access less water. The fish bone systems in this experimental site was dug out by forest department and abandoned, which we took for this experimental project. In overall view, the natural mangroves grown faster and dominate a major part of mangrove coverage area in the restoration site. The planted mangroves also growing well, but they struggle each for space and water accessibility. Hence, we recommend carrying ecological mangrove restoration method.
Before planting mangrove seedlings, we need to be clear about how our project objectives are suitable for the selected site. Mangrove creation, mangrove extension and mangrove restoration are different activities that will create quite different impacts on existing local ecosystems. Unfortunately all the mangrove projects are named as “mangrove restoration project” in our country.
Salt marshes are also important coastal ecosystems that always exist adjacent to mangroves. They have their unique features. Mud flats are the feeding grounds for a variety of birds, including migratory birds. Estuaries are also having their unique flora and fauna, which is different from mangrove environment in physical, biological and ecological settings. There is no need for having mangroves in all the estuaries, although mangroves are the plants growing where freshwater mix with sea water.
There are several mangrove projects that actually invaded into mudflats, estuaries and salt marshes to plant mangroves, without doing mangrove restoration in the degraded mangrove site. Millions of funds, time and human energy have wasted, just because of not selecting a suitable site. So, site selection is a vital part of any mangrove project. If a project manager found a suitable site after analyzing all of its criteria, then the project will be successful. Even without digging huge canals, planting thousands of seedlings, mangrove restoration can be done by simply doing ecological restoration techniques.
• Most imporant part of the project
• Decides the success or failure of the project
• Traditional knowledge is effective in site selection
• Field experience and local community participation is important
• No scientific techniques are needed, except for monitoring and documentation
I took some photos, while visiting Krishna estuary in Andhara Pradesh (below).
Based on the field observations and interaction with local villagers, the sites were not selected for restoration.
Picture 3: This site was sandy in the upstream of estuary. See some terrestrial grasses growing. Although it was easily accesible, the substratum was not fit for mangroves and no natural mangrove stands available adjacent to this site.
Picture 4: This site had naturally dispersed seeds. See the seedlings coming out, which is an indication of suitable substratum. However, look at the foot paths of cattle and man. Local villagers told that growing mangrove here will disturb their accessibility, so it was not selected.
Picture 5: This site was in higher elevation than other site, with strong clay substratum. It was also not selected.
Picture 6: This site has natural mangroves on both side. Looks nice for mangrove restoration. But, there was a plenty of seed availability, dispersal and natural seedling growth here. So, there was no need to resotre/grow/create mangrove here. Planting mangrove in such exposed river beds in low tide (look at the centre of river) would block/turn monsoon river flow in to other direction. I saw a presentation from a mangrove restoration project from Sundarbans. They did a mistake to plant mangrove seedlings in the exposed river bed in low tide. If a village settlement is located in any side of that river, then the mangrove plantation project would lead to disaster.
Picture 8: This site already had a plenty of mangrove seedlings through natural dispersal. Preventing external threats to such site can lead to natural mangrove regeneration. No mangrove plantation should be carried out in such sites. See dense settlement of seeds/seedling in a small area. These seedlings can be used for transplantation to suitable degraded site in suitable season, if there is no possibility of natural seed availability. It would reduce the cost for nursery establishment and maintenance. We observed that natural seedlings collected from the wild mangrove sites can easily adapt themselves to new plantation sites, when compared to direct seed sowing or nursery raised seedlings. Again, suitable site matters for mangrove regeneration.
Picture 9: I used to show to mangrove restoration beginners/students to show how to select suitable soil for mangrove plantation. The above photos shows my feet standing in diferent substratums. Hard mudflat, fine silt, beach, eroded soil, hypersaline mudflat after rainfall, elevated sand dune and mangrove clayey soil. The last photo with smiley shows that mangrove seedlings can easily extend their roots, get moiture and grow, which is not possible in other substratum. Although several other factors influence mangrove seedling growth, I used these pictures to create interest among students/volunteers in mangrove site selection.
Sincere thanks to