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SECRETS OF MANGROVE RESTORATION REVEALED! Version 4.0

1984:

BEFORE

1989:

AFTER

Lewis Environmental Services, Inc., and its president Roy R."Robin" Lewis III, have designed and constructed over 30 successful mangrove restoration projects ranging from less than an hectare to more than 500 hectares. These projects are located in Florida, Puerto Rico, the U.S. Virgin Islands, and Nigeria. The two photographs accompanying this portion of our web page show one of the sites near Miami, Florida, USA at the time construction was being completed (July 1985) and four years later on August 23, 1989. Most of the mangroves in this picture were volunteers (not planted, but from seeds that recruited naturally). The site covers 14 hectares, 6 of which were designed as open water habitat for fish production. We have also recently visited Cuba, where we are providing pro bono consulting services on methods of mangrove restoration in the Sabana-Camaguey, mangrove and seagrass ecosystem for the UNDP. We continue our research in Vietnam where we have found an experimental site to test restoration of an abandoned shrimp pond constructed in mangroves. Robin Lewis has recently returned from the Philippines where he is serving as a consultant to the Coastal Resource Management Project (CRMP) based in Cebu City.  The CRMP is implementing a program of mangrove management and restoration along 3000 km of shoreline designed to protect or restore 16,000 ha of mangroves. Based upon our 25 years of experience in this field, certain basic principles of successful mangrove forest restoration have evolved. We provide these here for the first time. We have several published papers that discuss many of these issues in more detail.

1. Determine the cause or causes for the death or disappearance of mangroves from the area of interest. If a chronic stressor is still present (i.e. extended flooding), it may prevent successful restoration. It is generally a waste of time and money just to attempt to replant mangroves without understanding why they died or why they have not recolonized on their own.

2. Make sure that any chronic stressor is removed. An example would be putting a culvert under a road that was constructed without regard for tidal flushing or freshwater drainage. It is very common to see such roads with dead mangroves on the isolated side, and healthy mangroves on the waterward side. Areas of mangroves that are diked also often suffer extended flooding. Reconnection to tidal waters is essential before restoration can proceed.

3. If removing or adding fill material to a restoration site is proposed, the design and careful monitoring of the final target grade (i.e. ground elevation relative to a surveyed datum or reference point) is very important. The single most common error made in mangrove restoration is the failure to reestablish the correct tidal hydrology. You must understand the depth and duration of flooding tolerances for the mangrove species you are dealing with. Typically, the elevation is designed too low, and thus tidal inundation is too deep and/or too frequent, and planted mangroves fail to thrive or die, and volunteer mangroves do not establish successfully. An elevation of 0.0 Mean Sea Level is typically too low. Check the range of elevations over which a stand of healthy mangroves is naturally established at a location as close as possible to your target restoration site, and plan on establishing a similar range at your site if you know for sure that the tidal range and pattern is the same. Different tidal ranges require different target elevation ranges.

4. An important component in mangrove forest restoration is the design and placement of tidal creeks and channels. Tidal streams provide access for fish and other mobile mangrove fauna, and allow for drainage of flood waters.

5. Before you decide to plant mangrove seeds or seedlings, determine if natural seed recruitment will occur. The need to actually replant mangroves varies greatly from site to site. The decision as to whether to plant, or to use nurse plant species like Batis, depends on the expertise of the design team and observations from similar areas over a period of years.

These basic principles have recently been summarized and presented at the Aquaculture '98 meeting in Las Vegas. You can request a copy of the abstract of this presentation at ”Contact Us". Ask for the Aquaculture '98 Abstract.  You can also directly access a PDF file of the recent US Army Corps of Engineers Tech report on mangrove restoration at:  http://www.wes.army.mil/el/wrtc/wrp/tnotes/vnrs3-2.pdf.

 

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