Cat Tien National Park

Ecology

Vegetation is varied and made up of seasonally flooding grassland and various types of tropical forest. The wetland is bounded to the east, south and west by dense humid evergreen forest with Hills supporting semi-evergreen and deciduous forest. A substantial part of Nam Cat Tien floods which significantly affects the flora and fauna found the area.

Vietnamese scientists have identified 5 major vegetation zones in Cat Tien National Park:

Evergreen forest: with dominant trees such as: Dipterocarpus alatus, Dipterocarpus intricatus (Dipterocarpaceae); Dalbergia alatus, Dalbergia mammosa, Pterocarpus macrocarpus (Fabaceae: Papilionoideae) and Afzelia xylocarpa (Fabaceae: Caesalpinioideae).

Deciduous forest: trees with leaves that fall in dry season including: Lagerstroemia calyculata (Lythraceae), Tetrameles nudiflora (Datiscaceae), Anogeissus acuminata (Combretaceae).

Trees mixed with bamboo forest: this is secondary growth following 'slash and burn' agriculture, forest fires and pesticides (i.e. agent orange). With the forest canopy destroyed, bamboos (see below) and certain under-story trees become predominant including: Mesua sp. (Clusiaceae), Lagerstroemia calyculata (Lythraceae) Sindora siamensis and Xylia xylocarpa (Fabaceae: Mimosoideae).

Predominantly bamboo: resulting from human activity as above. Forest that has been cleared then abandoned, may be completely replaced by bamboos, which normally only predominate in areas prone to flooding. Two of the most frequent bamboo (Poaceae) genera are: Bambusa (especially B. procera) and Giagantochloa spp.

Grassy flood plains: Cat Tien National Park has large areas of swamp land, and unpolluted water resources. In the rainy season, the flooded area may exceed 2,500 ha - especially near the lakes (Bau Sau, Bau Chim and Bau Co).

The pictures above show boulder pathways, made to help visitors traverse some of the wetter areas during the rainy season - the significance of which may not be apparent during the dry season (right) This picture also shows rattan, a vine-like palm [Arecaeae], trailing on the forest floor (to left of the picture).

Recycling nutrients: termites and fungi

Tropical soils are often poor in plant nutrients and frequently acidic. The spectacular growth in a rain forest is largely supported by the efficiency of nutrient recycling after plants die and decay. Three groups of organisms: bacteria, fungi and arthropods are primarily responsible for this recycling, of which the latter two are most obvious.

Arthropod decomposers: include termites and millipedes

A nasute termite band.

This photograph was taken during the rainy season, but termites often form characteristic galleries in which give them protection from predators and dry air.

Their nests are frequently arboreal appearing as earth covered 'swellings' on tree trunks. Species in the genus Nasutitermes have "nasute" soldiers, with a head drawn to a point - from which they squirt a noxious sticky liquid if enemies attack. Unlike many other termite groups that have large jaws (mandibles), those of nasute termites are fused to the head capsule. The majority of this genus are associated with hardwoods, and may be timber pests in buildings. Identification from soldier caste with assistance from worker, nest habit and region of occurrence (species often having a strong geographical distribution).

Millipedes are important recyclers of leaf litter

They can be distinguished from centipedes (which are usually carnivorous) by apparently having 2 pairs of legs per segment. Unlike centipedes they do not normally bite, but they may use a very unpleasant stink gland!

Fungi occur in many forms, with a confusing array of names.

They include mushrooms (implying that they are edible) and toadstools (some of which are deadly poisonous). Fungi are very important decomposers of wood, and some species, including the bracket fungi (below right), can be seen growing out of dead branches; many species are microscopic.

Dead animals don't escape the attention of ants for long!

This recently dead krait (Bungarus sp.), that was possibly killed by a mongoose has already attracted a trail of ants (detail bottom right) and a necrophagous fly (top centre).