The ecology of HCM City is classified into three typical systems based on the natural conditions: The tropical rainforest, the alum flooded forest, and the mangrove forest. The primeval forest almost no longer exists. However, a study of the forest is expected to help restore and develop a good ecological system for a large city in this tropical region.
The tropical rainforest
This forest exists in Cu Chi and Thu Duc districts. According to some research, the primeval forest in Cu Chi is a closed evergreen forest with the dominant plants being the dipterocarpaceae, the deciduous leguminosea and the lythraceae grown in the salient and umbelliferous layers. The dipterocarpaceae can be found at the secondary forest in Ben Dinh tunnel complex, with five species: dipterocarpus intricatus, shorea cochinchinensis, anisoptera costata, hopea odorata, and a famous species of precious wood that includes dalbergia bariensis, sindora siamensis, dalbergia cochinchinensis, dialium cochinchinensis, xylia dolabriformis and lagerstroemia tomentosa. The sub-canopy layer of the forest is home to the strychnos nux vomica, croton sp, peltophorum dasyrachi, grewia paniculata and wrightia annamensis. The forest in Cu Chi is damp and a little dry similar to that in Samat-Ca Tum in Tay Ninh Province, which is on ancient alluvial soil with a high content of sand and a wavelike territory.
The primeval forest in Thu Duc is like the typical tropical forest in the southeastern region, such as those in Ho Nai, Trang Bom and Ma Da in Dong Nai Province. It has a wavy territory with soil composed of ancient alluvia and several kinds of stones. The dominant trees are the humid dipterocarpaceae species such as the dipterocarpus alatus and dipterocarpus dyeri.
In the past years, along with the protection of the remaining secondary forests, mainly the coppice forest around Ben Duoc tunnel complex, Ben Dinh and Ho Bo in Cu Chi, efforts have been made to restore the closed evergreen forest and plant forests with large and precious wood. Also, a project to develop a botanical garden and a historical forest has been implemented. Another project is to build the national cultural and historical park on an area of 400 hectares in Long Binh in District 9, with the creation of a vegetation cover being one major goal. ·
The alum flooded forest
The natural vegetation on alum flooded land in HCM City is very poor. Large natural malaleuca leucadendron forests in southwest of Cu Chi, Binh Chanh, Hoc Mon and Nha Be districts almost no longer exist due to human exploitation and farming. Only some stretches of bush trees and several hectares of cultivated malaleuca trees are protected at the Tan Tao Experimental Station in Binh Chanh. This lowland area is home to the heleocharis dulcis, ischaemum indicum, acrostichum aureum, nymphea stellata and utricularia flexuosa. The highland area has the saccharum spontaneum, phragmites karka, acrocnychia laurifolia, annona glabra, melastoma affine, gardenia jasminoides and some species of leane.
After 1975, new economic settlements and farms were developed on alum land. Many kinds of crops and fruit trees were grown, such as paddy, sugarcane and pineapple. In addition, forest and tree planting were developed strongly, especially the acacia auriculiformis, acacia mangium and sesbania grandiflora. As a result, the alum flooded environment in the outskirts was improved and developed well. ·
The mangrove forest
The mangrove forest is mainly in Can Gio District, south of HCM City. It is a primeval forest developed along with the formation of alluvial ground at river estuaries and sea mouths. The dominant plant is the big-size rhizophora apiculata. The flora is diverse with 104 species of 48 families. Under French rule, the forest was a protected area. However, during the 1961-1970 period 80% of its area was destroyed by toxic defoliants sprayed by the U.S. military. During 1978-1986, HCM City authorities had tens of thousands of hectares of mangroves restored. In the brackish water area north of Can Gio, there are the nypa fruticans, cajuput, eucalyptus and cashew groves.
In general, the distribution of vegetation in mangrove forests depends on tide floods and soil solidity. Most vegetation familiar in mangrove forests in the South exists in Can Gio and is distributed according to different levels of terrain. They are the avicennia alba, avicennia officinalis, sonneratia alba, ceriop tagal, avicennia alba, phoenix paludosa, acrostichum aureum, excoecaria agallocha, lumnitzera racemosa and others.
With restoration efforts, the ecology of Can Gio mangrove forest has been improved. Animals have returned, such as crocodiles, monkeys, foxes, pythons, snakes and many bird species. Shrimp and fish production has also increased.
Besides protecting the land from encroachment by the sea, the Can Gio mangrove forest plays the role as a “lung” of HCM City, regulating its atmosphere. It also serves as a tourist area.