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Massive Mangrove Restoration Backfires
By David Malakoff
ScienceNOW Daily News
15 July 2008
One of the world's most intensive efforts to restore coastal mangrove forests is failing--in large part because people are planting the trees in the wrong places. Ironically, the restoration effort may also be harming other coastal habitats in the Philippines, according to a new study.
Over the past century, the islands that make up the Philippines have lost nearly three-quarters of their mangrove forests. The trees--which grow in brackish coastal waters on leggy roots--create key habitats for fish and shellfish. But settlers routinely cleared the flooded forests for development and ponds for fish farming. To reverse the trend, conservation groups began fanning out across the archipelago 2 decades ago, planting 44,000 hectares with hundreds of millions of mangrove seedlings.
Many of those trees were doomed to die quick deaths, according to biologists Maricar Samson and Rene Rollon of the University of the Philippines in Quezon City. In the current issue of Ambio, the researchers report that surveys of more than 70 restoration sites often found mostly dead, dying, or "dismally stunted" trees. The major problem, they say, is that planters didn't understand the mangrove's biological needs and placed seedlings in mudflats, sandflats, or sea-grass meadows that can't support the trees. Some of these areas have inadequate nutrients; in other places, strong winds and currents batter the seedlings. What's worse, the failed plantings sometimes pack a double ecological whammy, as restoration activities disturbed or damaged otherwise healthy habitats.
To get mangrove restoration back on track, Samson and Rollon say planters need better guidance on where to place the seedlings. Typically, the researchers say, the best locations are on gently sloping hill bottoms that are above mean sea level and flooded by the tides less than one-third of the time. The team says the Philippine government also needs to make it easier to convert abandoned or unproductive fish ponds back to mangrove swamps. But Samson admits this is a thorny legal and political issue, because landowners are reluctant to give up potentially valuable shorefront. As a result, the researchers write that they are "pessimistic about the 'voluntary surrender' of these pieces of wetlands back to nature."
The Philippines's dismal experience with mangrove restoration is not unique, says Roy "Robin" Lewis III, a prominent expert in the field and director of Lewis Environmental Services, a private restoration firm in Salt Springs, Florida. His studies have shown that mangrove restorers around the globe routinely fail to understand the tree's biology and that conflicts with landowners and political leaders can doom projects. Too often, he says, "ignorance and greed rule."
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Literature Citations:
Erftemeijer, P. L. A., and R. R. Lewis. 2000. Planting mangroves on intertidal mudflats: habitat restoration or habitat conversion? Pages 156-165 in Proceedings of the ECOTONE VIII Seminar "Enhancing Coastal Ecosystems Restoration for the 21st Century, Ranong, Thailand, 23-28 May 1999. Royal Forest Department of Thailand, Bangkok, Thailand.
Lewis, R. R. 1999. Key concepts in successful ecological restoration of mangrove forests. Pages 12-32 in Proceedings of the TCE-Workshop No. II, Coastal Environmental Improvement in Mangrove/Wetland Ecosystems, 18-23 August 1998, Ranong, Thailand. Danish-SE Asian Collaboration in Tropical Coastal Ecosystems (TCE) Research and Training. NACA, P.O. Box 1040, Bangkok, Thailand 10903
Lewis, R. R. 2000a. Don't forget wetland habitat protection and restoration for Florida's fisheries. National Wetlands Newsletter 22(6): 9-10 + 20.
Lewis, R. R. 2000b. Ecologically based goal setting in mangrove forest and tidal marsh restoration in Florida. Ecological Engineering 15(3-4): 191-198.
Lewis, R.R. 2005. Ecological engineering for successful management and restoration of mangrove forests. Ecological Engineering 24 (4 SI):403-418. (http://www.royrlewis.com/Ecol_Eng_Mangrove_Rest_Lewis_2005.pdf)
Lewis, R. R., and M. J. Marshall. 1998. Principles of successful restoration of shrimp aquaculture ponds back to mangrove forests. Page 327 in World Aquaculture Society Book of Abstracts, Aquaculture '98, Las Vegas, Nevada. (Abstract)
Lewis, R. R., and W. Streever. 2000. Restoration of mangrove habitat. Tech Note ERDC TN-WRP-VN-RS-3.2 U.S. Army, Corps of Engineers, Waterways Experiment Station, Vicksburg, Mississippi. 7 pp. (http://www.wes.army.mil/el/wrtc/wrp/tnotes/vnrs3-2.pdf)
Lewis, R. R., A. B. Hodgson, and G. S. Mauseth. 2005. Project facilitates the natural reseeding of mangrove forests (Florida). Ecological Restoration 23(4):276-77.
(http://www.mangroverestoration.com/LEWISH_1.PDF)
Stevenson, N. J., R. R. Lewis and P. R. Burbridge. 1999. Disused shrimp ponds and mangrove rehabilitation. Pages 277-297 in "An International Perspective on Wetland Rehabilitation", W. J. Streever (Ed.). Kluwer Academic Publishers, The Netherlands. 338 pp. (http://www.mangroverestoration.com/Stevenson_et_al_1999_Disused_Shrimp_Ponds.pdf)
Turner, R. E., and R. R. Lewis. 1997. Hydrologic restoration of coastal wetlands. Wetlands Ecol. Manage. 4(2):65-72.
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