Restoration of arid-zone mangroves in Balandra Lagoon
Yoav Bashan and Gerardo Toledo
Environmental Microbiology Group,
Dedication: This website is dedicated to the memory of the
Around 1991-1992, two sections of the arid climate mangrove forest at Balandra Lagoon in Baja California Sur, Mexico were illegally clear-cut, leaving bare areas with tree stumps. Natural re-vegetation of mangroves in arid climates is a very slow process that might take many years, if not aided by artificial reforestation of plants grown in greenhouses. In 1995, the area was still bare, with very few naturally grown small mangrove shrubs combined with large expanses of the short halophytic shrub Salicornia bigelovii, which is naturally associated with mangroves. It is possible that the propagules (reproducing plant parts that are equivalent to seeds in other plants) produced by the intact nearby mangrove, which might have had the potential to colonized these bare areas, were washed away by strong tidal currents. In this region, tides may fluctuate by one or two meters, and develop considerable velocity in the constricted channels in and around the mangrove.
After clear cut of the trees, before restoration.
Conventional reforestation of the entire area was impractical given the lack of sufficient resources and lack of government interest in restoration of mangroves. Mangroves were not protected wetlands until 2004. Therefore, an innovative approach was used. We planned to grow 500 black mangrove seedlings in a conventional nursery. The young trees would be replanted in a special manner to densely cover shallow, secondary feeding channels connecting this section of the destroyed mangrove to the central lagoon section of the intact mangrove ecosystem. This secondary channel, although very shallow (20-30 cm deep and up to 10 m width) drained a very large section of the forest containing two major deforested areas. The assumption was that when these trees grow, their lower branches would touch the water at high tide and block some floating propagules from washing into the open sea. Then the propagules would settle into the mud at low tide. Propagules of black mangroves germinating and establish quickly once they are planted. Further, it was assumed that, the more dense the forest becomes (consisting of the artificially planted and the retained plants), more propagules will be retained while the artificial reforestation will not interfere with the tidal cycle, which is essential for a healthy mangrove.
In September 1994, a mangrove nursery was established, using sand culture pots irrigated with seawater and planted with black mangroves (Avecinnea germinans). Some of the plants were inoculated with the nitrogen-fixing cyanobacteria Microcoleus sp., which was considered a potential plant growth-promoting bacteria. After four months, 500 seedlings were transplanted to the secondary feeding channel in one of the deforested areas. Apart from annual weeding of competing Salicornia shrubs, no special treatment was given to the area. To protect the reforested area from visitors from the nearby beach who used the mangroves as a toilet and garbage dump, a natural, shallow trench on the fringe of the mangroves was significantly deepened, filled with soft, silty mud, and prevented unauthorized entrance to the reforested area. The growth of the plants and maintenance of the area was conducted for three years, and then returned to the Mexican authorities for routine monitoring by the rangers of the Ministry of Ecology (SEMARNAT) and the environmental protection agency of Mexico (PROFEPA).
Outcome of the restoration program
In 2006, an inspection of the area showed a completely restored mangrove, including deforested areas drained by the same secondary feeding channel but far from the reforested area. Today, there is no way to distinguished between the natural primary forest and the area of secondary growth, except for the size of the trees. The area is like a dense jungle, is healthy, and does not need maintenance. In a 2005 survey of crab populations and tree size, the restored area had not completely recovered to the quality level of the intact mangrove stand, even a decade after the restoration. Perhaps more time is needed.
This website contained a photo gallery showing the area before, during, and after restoration, and a PowerPoint presentation showing the restoration work done (3.7MB), Lagoon's views (1.7MB), mangrove's views (1.0MB), wildlife inhabiting the ecosystem (1.7MB) and area around Balandra lagoon (video 12 MB). A technical paper published in the journal Hydrobiology in 2001 (PDF) summarized the technical details and the outcome of the work. It takes time to download presentation and video. Please, be patient.
Key words: Arid zone mangroves, Baja California, coastal restoration, coastal lagoon, tidal effects, wetlands.
The authors acknowledge the technical help of Angel Carrillo and Luis Romero in planting the trees; Adriana Rojas in monitoring their development in later years; and the Mexican authorities at SEMARNAT for allowing the restoration work in this area.
More information about mangroves in Balandra Lagoon and microbiology of arid-zone mangroves (PDF files):