Mangrove Restoration - Costs and Benefits of
Successful Ecological Restoration
Roy R. Lewis III
President, Lewis Environmental Services, Inc. P.O. Box 5430, Salt Springs, Florida, USA, 32134-5430.

Choice of Restoration Techniques
It has been reported that mangrove forests around the world can self-repair or successfully undergo secondary succession over periods of 15-30 years if: 1) the normal tidal hydrology is not disrupted and 2) the availability of waterborne seeds or seedlings (propagules) of mangroves from adjacent stands is not disrupted or blocked (Watson 1928, Lewis 1982, Cintron-Molero 1992). Because mangrove forests may recover without active restoration efforts, it has been recommended that restoration planning should first look at the potential existence of stresses such as blocked tidal inundation that might prevent secondary succession from occurring, and plan on removing that stress before attempting restoration (Hamilton and Snedaker 1985, Cintron-Molero 1992).
The second step is determine by observation if natural seedling recruitment is occurring once the stress has been removed. Only if natural recovery is not occurring should the third step of considering assisting natural recovery through planting be considered. Unfortunately, many mangrove restoration projects move immediately into planting of mangroves without determining why natural recovery has not occurred. There may even be a large capital investment in growing mangrove seedlings in a nursery before stress factors are assessed. This often results in major failures of planting efforts. For example, Sanyal (1998) has recently reported that between 1989 and 1995 9,050 ha of mangroves were planted in West Bengal, India with only a 1.52% success rate.
A similar large scale project in the Philippines is reported to have attempted the restoration of 22,723 ha of mangroves primarily by direct planting on mudflats and in existing seagrass meadows (Silliman University 1996, Lewis 1999, de Leon and White 1999). Plant survival varied from 0 to 66 % in a subsample of planted sites covering 491 ha, averaging 19% in Bohol and 17% in Cebu. On the other hand, careful data collection by Duke (1996) at an oil spill site in Panama showed that “…densities of natural recruits far exceeded both expected and observed densities of planted seedlings in both sheltered and exposed sites” (emphasis added).
Soemodihardjo et al. (1996) report that only 10% of a logged area in Tembilahan, Indonesia (715 ha) needed replanting because “The rest of the logged over area…had more than 2,500 natural seedlings per ha” (emphasis added).

Lewis and Marshall (1997) have suggested 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 the modifications of the previous mangrove environment that occurred that currently prevents natural secondary succession
4. Design the restoration program to initially restore the appropriate hydrology and 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 1-4 that natural recruitment will not provide the quantity of successfully established seedlings, rate of stabilization, or rate of growth of saplings established as goals for the restoration project.

These critical steps are often ignored and failure in most restoration projects can be traced to proceeding in the early stages directly to Step 5, without considering Steps 1-4. Lewis and Marshall (1997) refer to this approach as “gardening,” where simply planting mangroves is seen as all that is needed. Another common problem is the failure to understand the natural processes of secondary succession, and the value of utilizing nurse species like smooth cordgrass in situations where wave energy may be a problem. The recently introduced “encased replanting” technique (Riley 1995, Riley et al. 1999) for mangroves is an example of technological fix that has not been documented to work in medium to high wave energy sites in spite of the claims.

Next >>>