Topography and hydrology
Pa Co-Hang Kia Nature Reserve is located in the extreme west of Hoa Binh province, on the border with Son La province. The site lies in the limestone range that extends south-east from the Son La plateau to Cuc Phuong National Park. The main physical feature within Pa Co-Hang Kia is a high ridge, which reaches 1,536 m in the north-west of the nature reserve, and gradually decreases in altitude to the east. Most of the nature reserve lies above 500 m.
The geology of the site is characterised by limestone, which is partly of a non-karst nature, and has been eroded into a series of rugged, steep-sided hills between some flatter valleys. There are flat valley bottoms in the north of the nature reserve, in which are located a number of human settlements. Surface water is seasonal in the nature reserve, even in the populated valleys. Water sources dry up during the dry season, and rains are quickly absorbed into underground systems.
Scientists report that there are still hundreds of hectares of primary forest in the inaccessible limestone karst as well as on the high mountain peaks. However, most of the forest in the nature reserve is restricted to ridges and hill tops, while valley bottoms have been cleared for wet rice cultivation and lower slopes for shifting cultivation of maize and cassava.
Three orchid species thought to be new to science were recently discovered at the site, and the site may be of importance for the conservation of a number of other plant species of conservation concern. However, because the remaining forest at the site is heavily disturbed and fragmented, and continues to be degraded as a result of human activities, it is unlikely that Pa Co-Hang Kia is of high importance for the conservation of bird and mammal species.
Other documented values
Hang Kia cave, in Hang Kia commune, and the Hmong ethnic minority market in Pa Co commune receive small numbers of foreign tourists from Mai Chau village to the east.