Cai Lim karst depression on Tra Ngo Lon Island is located within Bai Tu Long National Park; this area is pristine and features unique vegetation compared to other mangrove forests in Vietnam.
Cai Lim Karst Depression – “Living Museum” on Bai Tu Long Bay
Bai Tu Long National Park covers an area of 15,783 ha, including the sea and emergent islands: Ba Mun, Tra Ngo Lon, Tra Ngo Nho, Sau Dong, Sau Nam… Cai Lim karst depression on Tra Ngo Lon Island is still very pristine, as if untouched by human presence.
Traveling by boat into Cai Lim karst depression. Photo: Quang Ninh Newspaper.
With a unique geological formation consisting of limestone mountain ranges surrounding a vast valley to form karst depressions, it creates a rich habitat for many species of flora and fauna. The main area of Cai Lim karst depression features a mangrove forest spanning about 10 ha.
Bat Cave in Cai Lim karst depression. Photo: Quang Ninh Newspaper.
Trees in the karst depression typically have a trunk diameter of around 30 cm and are hundreds of years old. Cai Lim karst depression does not have direct contact with sea water, but sea water flows through underground caves and rock crevices. When the rainy season arrives, the karst depression turns into a kingdom of frogs, snakes... alongside saltwater species such as shrimp, mud clams, horseshoe crabs... creating a diverse fauna.
Bats inside the cave. Photo: Quang Ninh Newspaper.
Bat Cave in the karst depression is home to hundreds of bats and monkeys. Monkeys are abundant here, including a breed of white-chested, golden-furred monkeys that have lived in the wild for many years. Each year, hundreds of long-tailed macaques confiscated by the Forest Protection Department are released on Ba Mun Island and Cai Lim karst depression.
Ancient mangrove trees. Photo: Quang Ninh Newspaper.
About 1 km north of Bat Cave is Cai De tunnel cave, which is also part of the karst depression complex. This is a submerged cave cutting through a mountain range about 500 m long, with the cave interior reaching about 60 m at its widest point. The cave can only be entered at low tide, while at high tide, water floods up to the cave roof. There are many mud clams here, making it a giant mud clam bed.
Large-sized mangrove plants. Photo: Quang Ninh Newspaper.
According to scientists, mangrove forests on Tra Ngo Lon Island in particular and in Bai Tu Long National Park in general lack alluvial deposition unlike mangrove forests in the Red River estuary area.
Venturing deep into Cai Lim karst depression, which is recognized for having unique vegetation compared to other mangrove areas in Vietnam, one encounters lush, dense bamboo groves as well as sea hibiscus forests. The sea hibiscus trees grow densely, with tiny saplings intertwining with centuries-old trees.
Spreading tree roots. Photo: Quang Ninh Newspaper.
In addition to sea hibiscus, there are also ancient blind-your-eye mangrove trees with trunks so massive that four people cannot wrap their arms around them. The deeper one ventures into the doline, the more wonders appear. A dense carpet of vegetation belonging to the orchid family clings to the limestone, including rare orchid species listed in the "Vietnam Red Data Book" such as the yellow lady's slipper orchid, jewel orchid, buffalo-ear orchid...
Rich flora. Photo: Quang Ninh Newspaper.
Perhaps that is why scientists have likened Cai Lim doline to a "living museum" that vividly illustrates the evolutionary history of species in Bai Tu Long Bay.
