Original karst tiankeng with underground virgin forest as an inaccessible refugia originated from a degraded surface flora in Yunnan, China.

Karst tiankengs are rare natural habitats, having a local microclimate different from surrounding regions. A contrast study on plant communities at the inside and outside of the primitive tiankeng was carried out by performing the qualitative analysis of species compositions of arborous and shrub layers. We found that plant communities in the primitive tiankeng belong to the subtropical moist evergreen broad-leaf forest, whereas those outside the tiankeng belong to subtropical semi-moist needle-broadleaved mixed forest. Trapped habitat of primitive karst tiankeng protects the plant communities significantly different from those in external karst ecosystems, so karst tiankeng has the great value in the plant species protection. Although the trapped habitat decreases plant species abundance inside tiankeng to some extent, highly diverse shrub species are present in the inside-tiankeng plant communities, and the primitive karst tiankeng plays an important role in the plant diversity protection. The primitive karst tiankeng is an important refugia for plant not only as a plant species protection library, but a plant diversity protection library. When implementing measures for the reduction of damages to biodiversity due to global climate changes and human activities, more attention should be paid to the primitive karst tiankeng as a small ecological refugia and biodiversity protection library.