Phong Nha Botanical Garden – A “Living Museum” Within the World Heritage Site

1. Overview of Phong Nha Botanical Garden

Phong Nha Botanical Garden is located at Km9 on Route 20 Quyet Thang, Bo Trach District, Quang Binh Province, approximately 45 km northwest of Dong Hoi City—equivalent to about one hour by road via the western branch of the Ho Chi Minh Highway. From the Phong Nha Tourism Center, it is just a further 12 km drive.

Approved for development in 2004 and officially opened in 2007, the garden originally covered 41.83 hectares and was expanded to 77.1 hectares in 2018. In 2014, it was designated as an Ecotourism and Environmental Interpretation Site, marking a significant milestone in the integrated approach to conservation and public education.

The garden is divided into four functional zones:

• Strictly protected area

• Natural regeneration area

• Plant collection and enrichment area

• Service and administration zone

This design reflects the diverse ecosystems of Phong Nha – Ke Bang, ranging from dense forests and limestone streams to multi-layered vegetation.

The garden hosts more than 150 plant species, including 77 valuable timber trees such as Green ironwood (Erythrophleum fordii), Burmese rosewood (Dalbergia oliveri), Stone pine (Calocedrus macrolepis), Black star (Hopea odorata), and Medium hardwood (Madhuca pasquieri), as well as many medicinal plants and useful species such as Stephania glabra, Jasminum subtriplinerve, and various orchids.

Beyond being a nature destination, the garden plays an important role in:

• Preserving the genetic resources of native flora, especially rare and endangered species of Phong Nha and Central Vietnam.

• Providing education and biological research opportunities for students, scientists, and local communities.

• Promoting responsible ecotourism, raising awareness about environmental protection and sustainable development.

 2. Forest Types and Their Characteristics in Phong Nha Botanical Garden

2.1 Forest Type Distribution

The plant communities within Phong Nha Botanical Garden are distributed across several key forest types:

• Evergreen broadleaf tropical moist forest on soil-based mountains (under 700 m elevation): Approx. 0.1 ha. Although a small area, it has high ecological value with relatively intact primary forest structure.

• Rich evergreen broadleaf forest: Approx. 10 ha with average timber volume below 70 m³/ha. Despite modest biomass, it shows strong regeneration potential due to favorable soil and climate.

• Medium-rich evergreen broadleaf forest: Approx. 2 ha. Represents transitional biodiversity zones aiding natural regeneration processes.

• Poor evergreen broadleaf forest: Covers 25.7 ha, mainly on ridge tops and steep slopes heavily affected by harsh natural conditions (sun, wind, poor soil) and past human activity.

• Disturbed evergreen forest on soil-based mountains: Largest area about 41 ha with forest structure disrupted by past logging or natural disasters.

2.2 Forest Type Characteristics

The poor forests, mainly found on high ridges and slopes, are exposed to severe environmental conditions and historical anthropogenic impacts (logging, shifting cultivation). Their canopy is broken, resulting in low cover (0.4–0.5) and abundant climbers creating gaps in the forest. However, natural regeneration remains promising:

• Tree density: Around 380 trees/ha, with dominant species including Tarrietia javanica, Erythrophleum fordii, Sindora tonkinensis, Machilus odoratissima, Syzygium cumini, Shorea thorelii, Parashorea chinensis, Castanopsis hystrix, and Ormosia balansae. These species are well adapted to nutrient-poor soils and harsh climates.

• Natural regeneration: Seedling density ranges from 2,200 to 2,800 trees/ha, unevenly distributed. Open areas with more sunlight show higher regeneration, forming potential "ecological islands." Regenerating species include Tarrietia javanica, Erythrophleum fordii, Sindora tonkinensis, Castanopsis hystrix, Ormosia balansae, Syzygium nervosum, Parashorea chinensis, and Shorea thorelii. This diversity indicates high ecosystem recovery potential, especially with proper management and protection.

The rich and medium forests, with more favorable soil and humidity, play a critical role in biodiversity conservation and ecological stability. Despite relatively low timber reserves (<70 m³/ha), their value lies in strong regeneration and high species richness:

• Canopy cover: Ranges from 0.2 to 0.3, creating ideal light conditions to stimulate regeneration and promote understory plant diversity.

• Regenerating tree density: Ranges from 2,500 to 3,200 trees/ha, with a diverse composition including Tarrietia javanica, Sindora tonkinensis, Hopea odorata, Erythrophleum fordii, Ormosia balansae, Shorea thorelii, Parashorea chinensis, Castanopsis hystrix, Garcinia cochinchinensis and other Garcinia spp., and Garcinia multiflora. These species provide both ecological and economic value, contributing to sustainable forestry programs.

• Ecological role: Rich and medium forests act as "ecological transfer stations," facilitating species dispersal from primary forests to degraded zones, thus accelerating ecosystem restoration.

3. Biodiversity

Situated in the core zone of the Phong Nha – Ke Bang World Natural Heritage Site, the Botanical Garden is an exceptional ecological reserve that shelters rich and endemic flora and fauna of Central Vietnam. With 513 vascular plant species, grouped in 327 genera, 122 families across four plant phyla, the garden functions as a “living museum” of native vegetation. Among them, 16 species are listed in the Vietnam Red Data Book (2007), 24 in Group IIA under Decree 84/2021/ND-CP, and 82 in the IUCN Red List (2020).

Biodiversity here is not only in numbers but in life forms and usage value. Fourteen life forms are identified, including 251 medicinal species such as Stephania glabra and Jasminum subtriplinerve; 163 timber species as the structural core of the forest; 54 edible plant species representing human-forest interdependence; and 8 ornamental species with ecological and aesthetic values.

In addition to flora, the garden is home to 343 vertebrate species forming a typical tropical forest ecosystem with high ecological interactions. These include 55 mammals—many of which are rare primates; 131 bird species essential for seed dispersal and insect control; 67 fish species, 59 reptiles, 31 amphibians, and 60 insect species, illustrating strong biodiversity at ground and aquatic levels. Notably, 11 mammal species and 4 bird species are listed in Vietnam’s Red Data Book, underlining the site's significance in conservation and biological research.

4. Climate and Hydrology

4.1 Climate

The garden lies within the tropical monsoon climate zone, with marked seasonal changes. Average annual temperatures range from 23°C to 25°C. The highest temperature ever recorded was 41.6°C (May 1992), and the lowest was 5.5°C (November 1993). Monthly temperatures vary greatly, peaking in July and reaching their lowest in January. Daily temperature ranges around 10°C in summer and 8°C in winter.

Annual rainfall averages 2,000–2,500 mm, with mountainous areas reaching up to 3,000 mm, mostly concentrated between September and November. Even in the dry season, there are at least 10 rainy days/month (“minor rains”), and evaporation ranges between 1,000–1,300 mm annually.

Average annual humidity is 83–84%, dropping to 66–68% during the dry season and sometimes as low as 28% during strong southwest winds (Lao winds). The area is influenced by two dominant wind patterns: northeast monsoon (Nov–Jan) and hot southwest monsoon (May–Aug).

Flood season lasts from September to November, with peak floods typically in September–October. However, due to its elevation and good drainage, the garden rarely suffers waterlogging. During the dry season (Jan–Jul), stream water levels drop significantly, sometimes causing drought stress. Occasionally, minor rains in May–June cause water to rise up to 1 meter, enriching habitat variety and influencing plant distribution.

4.2 Hydrology

The garden features three small streams and one major creek that combine into a perennial waterfall. This system is not only vital for ecosystem hydration but also enhances landscape aesthetics, supporting the area’s ecotourism value.

5. Topography, Geology, and Soil

5.1 Topography

Phong Nha Botanical Garden lies in a transitional zone between limestone and soil-based mountains. Limestone areas cover about 23% of the land—part of the extended Phong Nha – Ke Bang massif—rising 200–300 m with slopes over 40°, featuring monolithic, non-stratified rock ideal for drought-tolerant endemic flora.

The remaining 77% consists of soil-based hills in the southeastern belt, averaging 300–400 m in elevation with gentler slopes, suitable for large timber trees, medicinal plants, and resident bird habitats. Elevation ranges between 150–250 m. Terrain varies markedly: above 180 m, slopes average 20–25°, reaching 60° locally; below 180 m, the land is flatter (<5°), following stream beds where moisture-loving plants thrive.

This interplay of rock and soil forms a highly diverse terrain, fostering distinctive tropical rainforest habitats.

5.2 Geology

The garden sits on ancient Devonian-era (419–359 million years ago) bedrock composed mainly of two geological formations: La Khe and Long Dai.

La Khe Formation features shale, siltstone, and interbedded limestone. The shale is dark gray or bluish-gray, fine-textured, and often fossil-rich. Limestone is light gray, containing coral, brachiopods, and other marine fossils. Sandstone and conglomerate layers appear sporadically, indicating a coastal-depositional environment.

Long Dai Formation is similar in composition but more prominently features coarse terrestrial sediments, reflecting stronger fluvial influence. Both formations represent ancient shallow marine environments with organic-rich sediment accumulation.

5.3 Soils

The garden develops over two main parent rocks: limestone (43.7%) and sandstone (56.3%), giving rise to two principal soil types:

• Light yellow feralit soil on limestone (Fv): Found on slopes >80°, with high rock content (25–35%; up to 80–85% at Thac Gio area). Profiles consist of A–BC–C horizons, thin topsoil (6–10 cm), yellowish-brown color, and limited development.

• Yellow-brown feralit soil on sandstone (Fq): Found in lower streamside areas with slopes <8°. Profiles A–AB–BC, deeper topsoil (16–22 cm), brown to yellowish-brown, well-suited for secondary forest and native species growth.

Soil depth varies: 31.6% of the area has shallow soils (<30 cm), 41.3% medium (30–80 cm), and 27.1% deep soils (>80 cm), favoring diverse vegetation conservation.

6. Landscape and Infrastructure

6.1 Key Landscapes

• Rare timber forest: Located north of the garden center, this remnant of pre-1970s primary forest features ancient Erythrophleum fordii, Sindora tonkinensis, Hopea hainanensis, and Tarrietia javanica with trunks up to 3 meters in diameter, symbolizing ecological resilience.

• Thac Gio Waterfall: 500 m east of the center, this 30 m waterfall formed by Ba Khe Stream offers a refreshing microclimate ideal for adventurous activities like zip-lining, cliff sliding, or peaceful walks along a 50 m wooden bridge.

• Vang Anh Lake: Located west of the center and surrounded by a rehabilitated stand of the native Saraca dives (Vang Anh), it provides a tranquil scenic spot with rich ecological value.

• Dan Cave: A significant natural and historical site, once used as a wartime shelter by locals and soldiers. The limestone chamber offers a stable microclimate ideal for bats and cave-dwelling species, making it valuable for biodiversity studies in low-light, high-humidity environments.

• Ancient Gua tree (Alangium chinense): Found near the interpretation trail, this native specimen with a girth of nearly 3 meters and an estimated age of hundreds of years is both an ecological relic and a genetic resource, featured in environmental education programs highlighting old-growth forest roles.

6.2 Infrastructure for Research and Education

• Specimen exhibition hall: Displays over 150 vascular plant samples, nearly 100 vertebrate specimens, and rare items like fossils of an ancient three-toed rhinoceros and the Laotian rock rat (Laonastes aenigmamus), as well as Calocedrus macrolepis, a highly endangered conifer.

• Ecological interpretation trail: A 4 km path guiding visitors through core ecological zones, offering hands-on environmental education.

• Native plant nursery: Covering over 1 hectare, the nursery has successfully propagated more than 120 native species such as Erythrophleum fordii, Chukrasia tabularis, Sindora tonkinensis, Calocedrus macrolepis, and Saraca dives for forest restoration and sustainable buffer zone development.

References

[1] Phong Nha – Ke Bang National Park. (2017). World Heritage Nomination Dossier: Natural Conditions. People's Committee of Quang Binh Province.

[2] Center for Rescue, Conservation and Development of Creatures. (2024). Revised Expansion Dossier of Phong Nha Botanical Garden. Phong Nha – Ke Bang National Park.

[3] Phong Nha – Ke Bang National Park. (2022). Catalogue of Flora and Fauna in Phong Nha – Ke Bang. Internal Publication.