Yang

Distributed across mainland Southeast Asia, including Myanmar, Thailand, Laos, Cambodia, Vietnam, and the Andaman Islands. The species occurs in lowland tropical evergreen and semi-evergreen forests, often along streams and in seasonally flooded areas, from sea level to approximately 500 m. It is particularly abundant in the mixed deciduous-evergreen forests of central Thailand and the Mekong River basin. The genus Dipterocarpus comprises about 70 species distributed across South and Southeast Asia, and is the type genus of the family Dipterocarpaceae.

A very large, resin-producing canopy to emergent tree: • Height: 40-55 m with trunk diameter 80-200 cm, with a tall, straight bole and large, spreading buttresses 2-4 m tall. • Bark: Dark brown to gray, deeply fissured and thick, exuding abundant clear to yellowish oleoresin from resin canals in the bark and wood. • Leaves: Large, simple, alternate, broadly ovate to elliptic, 15-30 cm long and 10-20 cm wide, leathery, glossy dark green above with prominent palmate venation; remarkably large leaves for a canopy tree. • Flowers: Large and showy for a dipterocarp, white to cream with a pinkish tinge, 3-4 cm across, with 5 petals and numerous stamens, in short axillary racemes. • Fruit: The largest dipterocarp fruit type—a large nut with 2 greatly enlarged, wing-like calyx lobes (hence "Dipterocarpus"—"two-winged fruit") 10-15 cm long and 3-5 cm wide, plus 3 smaller lobes. The two large wings spin the fruit as it falls. • Wood: Heartwood reddish-brown, moderately dense to dense (specific gravity 0.60-0.80), with prominent resin canals visible as dark streaks. • Oleoresin: Abundant, aromatic, used traditionally for waterproofing and illumination.

A dominant species of mainland Southeast Asian forests: • Habitat: Lowland evergreen and semi-evergreen forests, often along river terraces and in areas with seasonal flooding; tolerates brief inundation better than most dipterocarps. • Oleoresin production: Trees produce copious quantities of a valuable oleoresin (known as "yang" oil or "damar") from canals in the bark and wood; the resin hardens on exposure to air into a hard, golden varnish. • Phenology: Flowers annually or near-annually (more regularly than many Shorea species), producing large, distinctive winged fruits. • Pollination: Large, showy flowers attract moths and beetles. • Seed dispersal: The two large wings on the fruit create an effective autorotation mechanism, but the heavy fruits typically travel only 30-80 m from the parent tree. • Regeneration: Seedlings establish in partial shade and can persist in the understory; growth is moderate. • Ecological role: A dominant canopy species in the mixed forests of central Thailand and the Mekong basin, providing food for elephants, wild cattle (gaur and banteng), and numerous bird species that consume fallen fruits. • Cultural significance: Yang trees are often preserved as sacred trees around Buddhist temples in Thailand and Cambodia.

Listed as Endangered on the IUCN Red List. The species faces severe threats across mainland Southeast Asia: • Heavy logging for its valuable, durable timber has depleted populations throughout its range; the species has been one of the most commercially important dipterocarps in Thailand, Cambodia, and Myanmar. • Lowland evergreen forests in mainland Southeast Asia have been extensively cleared for agriculture, rubber plantations, and urbanization. • Oleoresin tapping, while providing economic value, can damage trees if done unsustainably. • The Mekong River basin forests, where the species was once abundant, have been heavily degraded. • Thailand has established several protected areas containing Yang populations, including Huai Kha Khaeng Wildlife Sanctuary (UNESCO World Heritage Site). • Community forestry programs in Thailand promote sustainable resin tapping as an alternative to logging. • Vietnam has designated the species as a priority for conservation, with remaining populations in Yok Don and Cat Tien National Parks. • The species' cultural significance as a temple tree provides some informal protection.

Valuable for reforestation in mainland Southeast Asia: • Seeds: Large, recalcitrant seeds that germinate within 5-15 days; viability is short (1-3 weeks). The large seeds contain substantial energy reserves that support initial seedling growth. • Growth rate: Moderate, approximately 1-2 m/year under favorable conditions; faster than many Shorea species. • Soil: Prefers deep, moist, alluvial soils along rivers and in valleys; tolerates seasonal waterlogging. • Light: Seedlings tolerate moderate shade; mature trees require canopy exposure. • Oleoresin tapping: Trees can be tapped for resin starting at approximately 15-20 years by making diagonal cuts in the bark; sustainable tapping produces 2-5 kg of resin per tree per year without killing the tree. • Spacing: 6-10 m in enrichment plantings. • Reforestation: One of the most commonly planted dipterocarps in Thailand for reforestation of degraded lowland forests. • Cultural planting: Frequently planted around Buddhist temples and monasteries in Thailand and Cambodia. • Challenge: Large seeds are difficult to store and transport, limiting distribution to planting sites.

A cornerstone species of mainland Southeast Asian forestry: • Timber: One of the most important commercial timbers in mainland Southeast Asia, used for heavy construction, bridges, railway sleepers, boat building, and flooring. The resin-impregnated wood is naturally durable and resistant to termites. • Oleoresin: The "yang" resin is used traditionally for waterproofing boats, caulking, torch fuel, and incense; modern uses include varnish and paint manufacturing. • Cultural: Yang trees are preserved as sacred trees around Buddhist temples throughout Thailand and Cambodia; some temple Yang trees are estimated to be over 300 years old. • Traditional medicine: Resin used for treating skin conditions, wounds, and respiratory ailments. • Reforestation: A priority species for reforestation programs in Thailand and Cambodia due to its fast growth and ecological importance. • Ecological: Fallen fruits provide food for elephants and other large mammals during the dry season. • Carbon storage: Large, long-lived trees store significant quantities of carbon in their massive trunks and root systems.