Can Gio Mangroves cover an area of about 38,750 ha and occupy 54,2% of the total natural land of the district. In the second Indochina war, the dense mangroves were severely destroyed by bombs and herbicides sprayed. Many animals were killed or migrated to other areas.
Severe erosion was observed in the dead mangrove areas and along the river banks. A large area of bare land has turned into acid sulfate soil.
Rehabilitation is a joint effort of Ho Chi Minh City’s people. An extensive reforestation programme was undertaken after the war (1978). Now the majority of the sprayed area is covered by replanted and regenerated mangrove vegetation. The rehabilitation has resulted in the increase of biodiversity in terms of flora, plant communities, plankton, benthos, fish, amphibians, reptiles, birds and mammals. It has also led to positive changes in the physio-chemical properties of the soil and water. Environmental improvement has been observed in the rapid accretion of mud flats along the river banks and the mitigation of erosion and salt intrusion, as well as pollution.
Forest management activities and forest allocation for local dwellers have been implemented in recent years to bring about an improvement in ecosystem resource management and successful conservation.
The results gained from the restoration and conservation work have changed the landscape and the life of local dwellers in a good direction. Can Gio Mangrove Forests have just been recognized by UNESCO/MAB as the Mangrove Biosphere Reserve.
Country or Territory:
Estuaries, Marshes & Mangroves
Area being restored:
Primary Causes of DegradationDeforestation
During the Vietnam War, mangrove forests in Can Gio were one of the resistance bases in the Southeast of Vietnam. Consequently, they were extensively damaged by bombs and herbicides such as áâ‚¬Å“agent orange,áâ‚¬Â as well as white agent and blue agent. From 1966 to 1970, with the launching of Operation Ranch Hand, the US Air Force sprayed 1,017,515 gallons of herbicides and defoliants (Ross, 1975), destroying the mangrove area in Can Gio. Of the 291 000 ha of total mangrove area in southern Viet Nam, 105 000 ha, or 36 percent, were sprayed one or more times.
Heavy defoliation has not only exterminated the vegetation but also destroyed the heterotrophic elements and changed the whole ecosystem. (Hong & San, 1993). A number of terrestrial animals and birds were killed, although some migrated to safe areas. It was found that for a few years after the defoliation, fish, crustaceans and mollusks benefited from the abundant food created by the decomposition of fallen mangroves and other organic matter. However, their numbers decreased again within three years (Hong & Tri, 1986). Some species such as crocodiles and tigers became extinct, while monkeys, lizards and birds, which used to be found in great numbers in the mangroves, also decreased gradually after the war.
Without the protection that mangroves offer against tides, waves and water currents, severe coastal and riverbank erosion occurred. Comparison of sprayed areas in 1958 and 1989 has shown that the percentage of water surface further increased to 31.2% (Nam et. al., 1992). Forest soil was chemically changed because of the loss of protective vegetation cover, with lower pH from insufficient freshwater in the dry season and higher salinity because of increased evaporation.
Reference Ecosystem Description
From 1917 all mangrove forests were periodically exploited by the Water – Forestry Bureau of the French Colonial Government. In 1929, the French colonists enacted a measure to conserve the forbidden mangrove forests in Quang Xuyen and Can Gio Districts (Nam & Quy, 1999). The favorable natural conditions and the adequate management brought about the strong development of mangroves. The dominant species was 12-15m in height and 20-30 cm in diameter on average.
Vu Van Cuong (1964) divided the mangrove vegetation in this area into two groups as follows:
Salty water community group —
– The pioneer community of Sonneratia alba and Avicennia alba grew on the new mud flat of estuaries. The pioneer population of Avicennia alba developed along the river banks.
– The community of Rhizophora apiculata and Sonneratia alba (50% and 20% respectively) was formed on the mud flat that has become stable thanks to the pioneer community or population. The mangrove tree was 8-10m in height. In the community, Xylocarpus granatum, Kandelia candel, Derris trifoliata and Aegiceras corniculatum could be found as well.
– X. granatum and R.apiculata community was established on the land inundated at the level of 2-2.5 m. R. apiculata was 15-18m in height. Other species seen were Ceriops tagal, A.alba and X. granatum. This is a commonly found community in the mangrove areas.
– The community of R. apiculata and Ceriops tagal was distributed on the mud flats flooded by tides at the level of 2.5-3m. R. apiculata was dominant here with the height of over 10m. A. officinalis, X. granatum, X. moluccensis and C. decandra were also observed in this community.
– On the mud flat inundated by tides at the level of 2.5-3.0m was Avicennia officinalis and Ceriops decandra. Other species found comprised X.moluccensis, C.tagal and Lumnitzera littoralis.
– The community of Excoecaria agalocha and Phoenix paludosa was observed on the land only flooded by high tides (3.3-4.0 m). Additionally, X.moluccensis, C.tagal, Acrostichum aureum, Heritiera littoralis and Flagellaria indica were present.
Brackish water community group —
The group was distributed along the riverbanks of brackish water areas in the north of Can Gio District and along Dong Nai Estuary. There were 4 communities classified as follows:
– In the areas inundated by 1-1.5m high tides, the pioneer species found was Sonneratia caseolaris 8-10m in height.
– In the areas flooded by tides 1.5-2 m in height, the community of Cryptocoryne ciliata and Acanthus ebracteatus was formed with other species namely Nypa fruticans, Cyperus malaccensis and Derris heterophylla.
– In the areas flooded by tides at the level of 2-3m was the community of Annona reticulata and Flagellaria indica. Other species included Amoora acuculata, Barringtonia acutangula and Gardenia lucida. The mangrove trees were 6-8 m tall.
– In the areas inundated by 3-4m high tides, there was a community of Melastoma polyanthum and Dalbergia candenatensis formed with other species of Pandanus tectorius, Glochidion littorale, Hibiscus tiliaceus, Thespesia populnea, Clerodendron inerme and Pluchea indica.
There were no statistic data on animals in Can Gio. Yet the old inhabitants said that before the August revolution, a lot of terrestrial animals had lived in the mangroves such as deer, monkeys, sambars, pythons, varans, tigers, etc. Sometimes, crocodiles could be found in Dong Tranh and Soai Rap Rivers. The names of some channels proved the presence of these animals such as: Crocodile channel, wild boar channel, wolf channel … (Hong (ed.), 1997)
– to restore the mangrove ecosystem previously destroyed by herbicides;
– to stabilize the land and restrict erosion;
– to contribute to the improvement of the environment by reducing the pollution caused by industrial waste and smoke discharge;
– to create habitats for terrestrial animals and provide nursery breeding grounds for aquatic resources.
– to create employment and raise the income of foresters and fisherfolk through silviculture and aquaculture activities, so improving the standard of living of local inhabitants;
– to supply part of the demand for fuelwood and poles.
The project does not have a monitoring plan.
Description of Project Activities:
From 1978 to 1997, 20,638 ha of mangroves in Can Gio were under reforestation (Tuan,1998). The main species planted were the fast-growing Rhizophora apiculata (the main economic species) and other species such as Nypa friticans, Ceriops tagal and Rhizophora mucronata.
Ecological Outcomes Achieved
Eliminate existing threats to the ecosystem:
By 1996, nearly 35 000 ha of mangrove forest had been replanted in Can Gio; of these, about 20 000 ha are now growing well. Previously, the coastal area and riverbanks of Can Gio suffered from extensive erosion when the northeast monsoons blew. After certain years of rehabilitation, mud flats have been formed along the riverbanks and subject to erosion caused by wave and tide actions. At the beginning of November 1997, an unusual storm hit the coastal zone of Southern Vietnam caused a serious damage to many coastal provinces. Yet, the mangrove belt in Can Gio helped a lot in mitigating the loss resulting from the storm. The rehabilitation of mangrove forests has brought about certain changes in the physical and chemical properties of soil in the area. The substrate has been gradually transformed into loam and the pH value subsequently increased, indicating the reduction in soil acidity. Due to the development of mangrove pioneer species such as Avicennia alba and Sonneratia ovata, erosion at riverbanks has been reduced; the accretions have developed strongly, creating large tidal sandy mud flats for blood ark-shell and clam farming. Mangrove rehabilitation combined with water regulation of Tri An and Dau Tieng reservoirs has contributed to reducing salt intrusion in the agricultural production areas of Can Gio and neighboring districts both in the rainy and dry seasons. The rehabilitation of mangroves at Can Gio has resulted in a dramatic increase in biodiversity, and the site is recognized at present as a Mangrove Biosphere Reserve. The following is a detailed list of the natural resources that have been restored at Can Gio. Flora -- Compared to the flora investigated by Cuong (1964) before the warring herbicide spraying, the natural mangrove flora now is similar, but the individual number and dispersion is not the same. Our investigation has listed 72 flora species, 30 of which are true mangroves and 42 associate mangrove species. Besides the mangrove flora, 95 species belonging to 42 families of inland plants dispersed by humans and animals have been found. These species form the diverse communities on different biotopes. Vegetation -- Today, the mangroves in Can Gio are more diverse in community structure compared to those before the wars. An explanation for this is that in Can Gio Mangroves, valuable species mixed with naturally regenerated ones have been rehabilitated. Some are found naturally regenerating on abandoned shrimp ponds. Below is some main communities Communities in areas of high salt concentrations: 1. The pioneer community of Sonneratia alba - Avicennia alba can be found on the coastal and estuarine newly accreted lands daily flooded by tides. The salinity here is high. 2. The pioneer population of A. alba is present on the newly formed mud flats along the rivers and creeks. 3. Rhizophora apiculata and Avicennia alba community is seen between the replanted R. apiculata and the population of A. alba naturally regenerating on deep muddy soil. 4. R. apiculata and A.officinalis community is distributed on firm mud flats flooded by normal high tides. These two species are found naturally regenerating in groups. 5. The community of R. apiculata - Lumnitzera racemosa and Ceriops decandra is formed on firm mud lands flooded by spring tides. Only R. apiculata was planted between 1981 and 1985 and later on chopped down, leaving behind bare areas and naturally regenerated shrubs. 6. The community of R.mucronata - Phoenix paludosa and Lumnitzera racemosa grows on firm mud flats flooded by spring tide. Phoenix was burnt to spare land for Rhizophora planting. After that, the species vigorously regenerate from stumps in rainy season. 7. The community of Ceriops tagal - C. decandra can be seen on sandy mud flats flooded by spring tides. Dominant species is C. tagal. R. apiculata and L. racemosa are sparsely distributed. 8. The community of Phoenix paludosa and Acrostichum aureum is on firm sandy clay flats only flooded by spring tides. The associate species are L.racemosa, Excoecaria agallocha and Pluchea indica. 9. The population of Excoecaria agallocha is formed on the firm sandy/loam flats. 10. Avicennia lanata population regenerates on the high land of sandy clay or on the substrate of abandoned salt pans. 11. On waste lands of firm sandy clay or former salt pans and shrimp ponds is the population of Sesuvium portulacastrum. Brackish water communities: In general, brackish water communities at present are not very much different from those found prior to the wars. Some main communities are: - Pioneer community of Sonneratia caseolaris - Avicennia alba - Pure Nypa fruticans population - Nypa fruticans - Acanthus ilicifolius - Cryptocorine ciliata community - Sonneratia caseolaris -Nypa fruticans community - Annona reticulata - Flagellaria indica community Plankton -- The analysis of 52 water samples of plankton from different points in the directions of north-south and east-west in Can Gio by Viet (1993) has given the following results. There were 63 phytoplankton species and 19 zooplankton species found. Zooplankton increased considerably in the samples collected in June 1993 (100,000-1,000,000 cells/mÁ‚Â³) in comparison with that in June, 1990 (67,000-6,025,000 cells/mÁ‚Â³). Benthos -- Mangrove rehabilitation has changed the soil's properties thanks to the sediments formed by litter fall with the help of large quantities of fine and fibrous root matter. The mud has the highest concentrations of organic carbon and nitrogen (Alongi & Sasekumar, 1992). This has directly influenced the distribution of benthos. On the other hand, benthos play an important role in the decomposition of litter fall. Through our preliminary surveys, 115 species of invertebrate macro-benthos have been listed. Polychaeta has 34 species of 19 families; Mollusca comprises Gastropoda class with 18 species belonging to 12 families and Bivalve class with 11 species of 8 families. In Crustacea class, 27 species belonging to 9 families of Macrura and 25 species in 5 families of Brachyura have been found. (Anon, 1998) Fish -- Fish use mangrove waters as nursery grounds, permanent habitats or breeding grounds (Aksornkoae, 1993). 134 species belonging to 40 families have been found, the majority of them are true estuarine species and the remaining are eurythermal and euryhaline fishes. Most species live in shallow waters and often enter estuaries for feeding (Tang, 1984; Mien et al., 1992). Recently, Pangasius polyuranodon and Mugil affinis have developed rapidly, especially in the rivers with abundant Avicennia alba and A. officinalis; Lates calcarifer concentrate in shrimp ponds. Priophthalmus schloserri used to be rare but have now become rather common, particularly at the mud flats near salty water river mouths. Amphibians -- Preliminary surveys show that there are 9 species belonging to the 4 amphibian families. The tree frogs (Racophous leucomystax) are commonly found. Their loud croaks can often be heard in the forests. They breed in the rainy season - a foamy secretion is left on the trees as a result of mass copulation. Cricket frog (Rana limnocharis) is mainly seen not only in the rice fields but in the brackish water mangroves as well. The common toad (Bufo melanostictus) is often seen in guardhouses where there are a lot of mosquitoes. Reptiles -- Of the 30 species of 13 families found in Can Gio, 8 species belong to the family Colubridae and 3 belong to Cheloniidae, the remaining is only found in the large rivers and sea shore. The King cobra (Ophiophagus hannah) is distributed throughout the natural and replanted forests, while Naja naja is widely distributed in the villager gardens. A number of aquatic snakes such as Achrochordus javanicus, Lapenius hardwickii and marine turtles as Chelonia mydas, Leidochelys olivacea are only caught in the sea shore by fishing nets. In 1983, some workers at the enterprise shot a crocodile, but since then no other crocodiles have appeared. Only 30 crocodiles (Crocodylus porosus) have been reared at the Can Gio Forestry Park. Since the 1990s, thanks to the effective protection of forests, many birds have come and consequently a number of reptiles eating bird eggs or young birds such as varans, boas, and snakes have increased. Birds -- From 1975 to 1980, birds were very rare in Can Gio Mangrove areas, especially on the high land only flooded at high tide as birds' dung was rarely seen on the ground or near tree bases. Local people said only some river kingfishers were occasionally found perching on Avicennia branches or several little egrets (Egretta garzetta) or lesser sand plovers were seen searching for food on the mud flats far from villages. Since the 1980s, more and more birds have come back to the area. Besides waterfowls, many flocks of migratory birds from the North such as Charadrius alexandrius, Pluvialis squatarola, Pluvialis fulva and especially Tringa glareola, T. erythropus, Himantropus himantropus have been seen. Some water bird species make their nests from April to the next February in Phoenix padulosa stumps and Avicennia trees far from residential areas namely Egretta garzetta, Buteroides striatus, Bubuleus ibis. Along the mud flats of the rivers and creeks, which are periodically inundated, a number of wader species can be seen either feeding or roosting on the banks (Hussain et al., 1994). About 130 species of 44 families are known to occur in Can Gio. Of these, 51 species are waterfowls, including 21 migratory species. The rest is common in the delta and is seen in the different habitats (Dat, 1997). Birds play an important role in the ecosystem, contributing actively to the enrichment of the source of food in mangrove areas and making the soil fertile. Mammals -- 19 mammal species belonging 13 families and 5 species of chiropterans have been recorded (Dat, 1997). Among the terrestrial mammals, after mangrove restoration, the species with the most numerous individuals is macaques (Macaca facicularis), which lives in troops of 30 to 40 along the rivers and canals. Since 1992 they have multiplied very fast particularly in the forestry park. Everyday at the ebb tide, they often go to the flats to catch small crabs and mud skippers. Recently they have been fed by the forestry park's staff and tourists and hence have become more and more used to meeting people. The rodents develop strongly particularly the species in Muridae due to the increase of human population. Groups of wild boar (Sus serofa) are rather abundant in the P. paludosa patches. Sometimes local people see fishing cat (Felis viverrinus) on the natural Avicennia forests. This species is well adapted to the tidal areas and feeds on fish, birds, bandicoot, oysters and other small animals (Hussain et al., 1994). Generally speaking, the diversity of fauna within mangroves is high due to favorable food resources and a wide range of microhabitats - 6 types of microhabitats in mangrove forests recorded by Chapman (1975) as soil surface, soil interior, tide pools, small canals, fallen logs and tree canopy have been seen in Can Gio forests.
Factors limiting recovery of the ecosystem:
The reforestation in Can Gio was mainly done by youngsters and schoolchildren. Consequently, the technical aspects of reforestation were neglected and the survival rate was low. In the first years of the R. apiculata plantation, because of the lack of experience, the planting density was too high. Of the 29 583 ha of R. apiculata planted in Can Gio from 1978 to 1989, only 18 125 ha were covered with mangroves at the beginning of 1990. Through the 1980s, the success rate of the rehabilitation was further limited by inadequate management. A Forestry Enterprise made up of a small group of forestry workers, with insufficient means of transport and communication, was responsible for the protection of a vast area. Local inhabitants and nearby coastal dwellers, under economic stress, destroyed newly replanted mangroves through overharvesting for fuelwood and conversion to shrimp ponds.
Socio-Economic & Community Outcomes Achieved
Economic vitality and local livelihoods:
At the beginning of 2000, the Can Gio mangroves were designated for inclusion in the United Nations Educational, Scientific and Cultural Organization's World Network of Biosphere Reserves. From 1998 to 2001, ecotourism in Can Gio has developed rapidly. The troops of macaques, reared crocodiles and other wild mammals in the protected Can Gio Forestry Park have attracted many tourists. This development in ecotourism has contributed favorably to the socio-economic improvement of the local community. The mangrove restoration has also afforded good opportunities in biological research and conservation education. Recently, the Action for Mangrove Reforestation - Japan (ACTMANG) has supported Ho Chi Minh City to construct a model of Human Ecology Park in Can Gio Mangroves for Vietnamese and foreign students.
In May 1991, the government approved a project for the environmental protection of the forests of Ho Chi Minh City, and the People’s Committee invested funds and proper equipment to protect the forests. The Forestry Enterprise was converted into the Management Board of the City’s Environmentally Protected Forests (MBCEPF), personnel was increased and the city put into practice a policy of land and forest allocation to households. As a result, the destruction of forests markedly decreased.
Activities in the forest are now monitored and recorded. The main guard force includes workers from MBCEPF, workers from the agroforestry enterprises, employees of the Forestry Agency and households allocated forests to protect under 30-year contracts with MBCEPF. To date, 10 850 ha have been allocated to 208 household guards. The guards are given monthly salaries, 35 percent of the forest produce from thinnings, an allocation of 3 to 5 ha per household for aquaculture or salt ponds, assistance with difficulties and rewards for good protection of the forests. Other benefits to households include money to build houses on allocated land, boats for forest protection, loans for authorized fisheries production, and technical help through short training courses on thinning, reforestation and shrimp farming.
Sources and Amounts of Funding
People’s Committee of Ho Chi Minh City
Hong, P.N. 1996. Restoration of mangrove ecosystems in Vietnam: a case study of Can Gio District, Ho Chi Minh City. In C. Field, ed. Restoration of mangrove ecosystems, p. 76-79. Okinawa, Japan, International Society for Mangrove Ecosystems and International Tropical Timber Organization (ITTO).
Hong, P.N. 2001. Severe impacts of herbicides on mangroves in the Vietnam war and ecological effects of reforestation. Paper presented at the Centre for Excellence (COE) international seminar “Changing People-Environment Interactions in Contemporary Asia: An Area Study Aproach”, Kyoto, Japan, 15-17 November.
Centre for Natural Resources and Environmental Studies
Vietnam National University —
UNESCO MAB Biosphere Reserve Directory