The forest spread over three communes of Ha Trung District, viz., Ha Tan, Ha Dong and Ha Linh, is about 25 km from Thanh Hoa capital.
The trees, known as sen or sen mat in Vietnamese, are scattered on low hills, at an altitude of 50-325 m. This is one of nearly 90 forest reserve areas that are strictly protected. When declared protected, the forest had an area of just 350 hectares, but now it has expanded to nearly 520 hectares.
Trinh Xuan Dac, 53 a Tam Quy forest ranger, checks and measures the diameter of a big tree in the forest with his arms. He said it has been estimated that there were tens of thousands of different large and small trees of the endangered species, but no detailed data on them.
"The biggest tree in Tam Quy is nearly 100 years old, about 70 cm in diameter. The arms of an adult can't reach around it, " he said.
The Madhuca pasquieri belongs to the sapodilla family (Sapotaceae) and Sapotales. They are found mainly in China, Vietnam and some Southeast Asian countries.
This forest houses precious trees that listed in the Red Book of endangered species in Vietnam. Residents entering and leaving the forest must strictly comply with legal regulations which prohibit cutting and burning. Many information signs have been placed at points that people pass.
In Vietnam, this tree grows mostly in the northeast, north-central and central coastal regions.
Given the wide area, rangers regularly patrol the forest on motorbike. In many places, Dac and his colleagues have to walk in the jungle to check "sensitive spots" that carry the risk of unwanted incursions.
Nguyen Van Chuong (L), Head of Tam Quy Forest Protection Center, and another ranger check an old tree for signs of pests and diseases.
Chuong said this tree is classified as part of a group of multi-purpose plants, and is listed in the group of four solid woods used in construction. Charcoal made with this wood has high heat that is used to forge all kinds of farm tools. No other coal can do this, he added.
Its fruit can be pressed to get cooking oil, replacing animal fat, and its leaves are ingredients in some folk medicines for skin diseases and burns.
Its fruits ripen at the end of the year. They have a sweet taste like sapodilla. People living around Tam Quy can go to the forest to pick up the fruit when the forest rangers allow them.
In recent years, another tree species, Erythrophleum fordii, has grown very strongly, the largest tree around 1.2 meters in diameter. What was once a single tree forest has become a mixed one now.