Forests in the Khao Yai National Park

Forests in Khao Yai National Park cover an area of about 200 sq km, on a line of mountains at the edge of the Northeastern Plateau. This has made Khao Yai a critical watershed, receiving rain from both Andaman and South China Sea monsoon winds. Most of the forest area in Khao Yai consists of expansive grasslands or primary rainforest comprising Dry Evergreen Forest, Mixed Deciduous Forest, Montane Rain Forest, Tropical Rain Forest and Secondary Forest, each of which is the habitat for a diverse flora and fauna.

Area
61%
Dry Evergreen Forest
840,000 rai (1,351.66 sq. km)
21%
Mixed Deciduous Forest
287,000 rai (459.84 sq. km)
8.1%
Lower Montane Rain Forest
111,187 rai (177.89 sq. km)
4.3%
Tropical Rain Forest
59,000 rai (94.88 sq. km)
3.7%
Grassland
51,835 rai (82.93 sq. km)
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Dry Evergreen Forest

At an elevation of 200-600m above mean sea level, this is the National Park's most extensive type of forest, covering 1,351.66 sq km, or 61.7% of the Park's total area. Similar to Tropical Rain Forest, the canopy is verdant, but deciduous trees are intermingled. Common tree species include Tetrameles nudiflora, Pterocymbium javanicum, Acrocarpus fraxinifolius (Pink Cedar), Lagerstroemia calyculata (Guava Crape Myrtle), Hopea odorata, Hopea ferrea, Shorea roxburghii, Dipterocarpus turbinatus, Dipterocarpus alatus (Resin tree), Dipterocarpus costatus, Aphanamixis polystachya and Zollingeria dongnaiensis, palms such as Areca triandra (wild areca palm), Corypha lecomtei and ground species such as Alocasia cucullata (Buddha’s hand), ginger and galangal-type roots, and pandan.

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Mixed Deciduous Forest

Found at 400-600m above sea level, this forest covers 459.84 sq km, or 21% of the forest cover. The trees are deciduous perennials such as Afzelia xylocarpa, Pterocarpus macrocarpus, Melia azedarach (Chinaberry), Lagerstroemia floribunda (Thai Crape Myrtle) and Wrightia religiosa (water jasmine). In the undergrowth throughout the forest are found bamboos and grasses and standing stones. In the dry season most trees shed their leaves to leave the canopy looking open, and wildfires are common. However, when the rains come back, the trees grow verdant leaves as before.

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Lower Montane Rain Forest

This is the highest forest in Khao Yai, found at elevations of 1,000m or more, in the area of Khao Khiew. Here the weather is cooler, and the area covered is 177.89 sq km, or 8.1% of the total forest. Plants encountered are softwoods such as Podocarpus nerifolius, Nageia wallichiana, Cephalotaxus griffthii, various species of Fagaceae and the “Moli Siam” (Reevesia pubescens var. siamensis), a single-habitat species

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Tropical Rain Forest

Tropical Rain Forest is thickly wooded forest ranging from 400 to 1,000 m above sea level, covering 94.88 sq km or 4.3% of the entire area. Most trees are of the Hopea or Pterocarpus genus, with tall trunks of 30-50m, with medium-sized and smaller plants able to live in the shade of the tall trees, including betels and palms. The forest floor and leaf litter nurture shrubs and annuals such as Salacca, Calameae (rattans), bamboos and creepers of many species. Tree trunks and branches are home to other plants such as ferns and mosses.

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Grassland

With an area of 82.93 sq km, these grasslands are the relics of past shifting cultivation. Before the creation of the National Park, most vegetation was grasses, mainly Imperata cylindrica (Cogon grass) interspersed with Phragmites karka (Tall reed), Fimbristylis insignis and Saccharum procerum. The vegetable fern (Diplazium esculentum) springs up regularly in areas prone to wildfire. Most noteworthy, during the 50 years that the National Park has been open, many grasslands have reverted to scrubland, which can become true forest again in the future.

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