China’s tiankengs are enormous, steep-sided karst depressions, and some shelter forests unlike those on the surrounding slopes. Their protected, humid interiors can serve as refuges for plants and animals—but “ancient ecosystem” does not mean every species or community has remained unchanged since deep time. Research also shows that isolation has costs: it can limit biological exchange even as it shields habitat from harsher conditions.
What is a tiankeng?
Tiankeng is commonly translated as “heavenly pit.” The term describes a large, steep-sided depression in carbonate rock—a kind of karst terrain shaped over long periods by water dissolving and moving through rock. A peer-reviewed study defines tiankengs as sinkhole-like depressions in carbonate formations, often hundreds of metres across or deep and connected to underground rivers during their development. The 2022 study in Scientific Reports and UNESCO Courier’s account by botanist Tang Jianmin both describe the landform.
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One proposed route to a tiankeng is the enlargement of an underground chamber followed by collapse of its roof. That is not a universal explanation: scientists have proposed multiple formation mechanisms, and there is no consensus that one process accounts for every site.
What lives in China’s giant sinkholes?
Some tiankeng bottoms hold forest communities and rare plants. Their steep walls and sheltered interiors can create conditions that differ from exposed karst terrain nearby. But a sinkhole is not automatically a pristine forest, nor does every tiankeng contain the same species.
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The 192-metre-deep forest in Guangxi
A forest in a 192-metre-deep sinkhole in Guangxi’s Leye County drew international attention in 2022. Tang Jianmin’s UNESCO Courier explainer, published in 2023 and updated in 2026, recounts the discovery and reports trees as tall as 40 metres alongside rare plants. Tang is an Associate Researcher at the Guangxi Institute of Botany, Chinese Academy of Sciences. This is a vivid example of a forested tiankeng, not proof that all such depressions contain untouched forests.
What the Damaosi comparison found
A 2022 study examined plant communities inside and outside the primitive Damaosi tiankeng in Yunnan. Inside, researchers identified subtropical moist evergreen broad-leaf forest; outside, the vegetation was subtropical semi-moist needle-broadleaved mixed forest. The study found a distinctive plant community with refuge value, while also reporting that conditions within the sinkhole reduced plant abundance to some extent. The finding supports a more careful conclusion than “sinkholes always have more biodiversity”: the communities can differ, and their ecological value comes with constraints.
What the biodiversity figures cover
Several striking counts refer to particular places and surveys, not to China’s tiankengs as a whole:
| Site or survey | Reported finding | Scope |
|---|---|---|
| Dashiwei sinkhole group, Guangxi | 29 sinkholes across 20 square kilometres | Figures from a Guangxi Forestry Department survey, reported by China’s National Forestry and Grassland Administration in 2024; these are not a national total. Administration report. |
| Dashiwei sinkhole group, Guangxi | 1,033 vascular plant species and 403 wild vertebrate species | Recorded for the group, not all within a single sinkhole; reported in the same 2024 administration account. Administration report. |
| Guangxi-wide survey | 72 state-key-protected wild plant species | A Guangxi-wide figure in Tang Jianmin’s UNESCO Courier account; it should not be read as a count for one tiankeng. UNESCO Courier. |
| Great Funnel, Xingwen UNESCO Global Geopark | 650 metres long diameter and 208 metres deep | Dimensions for this separate karst feature, not the Dashiwei group. UNESCO geopark profile. |
How isolation helps—and limits—wildlife
A tiankeng’s walls and sheltered bottom can buffer organisms from exposed surface conditions. That separation can help preserve habitat and rare species. It can also constrain movement and reproduction between populations, so a refuge is not necessarily a secure long-term solution by itself.
A 2026 Chinese Academy of Sciences research news item describes genomic work on the endangered tree Magnolia aromatica: 112 individuals across 26 populations were studied. The report says sinkholes can shelter the tree from harsh surface conditions while limiting gene flow and potentially diminishing long-term evolutionary potential. The institute’s news page is dated July 10 and gives July 14 as the study’s publication date; because those dates conflict chronologically, the journal publication date is not stated here as definitive. Chinese Academy of Sciences report.
Tang Jianmin calls tiankengs “a natural germplasm bank of biodiversity.” The phrase captures their value as refuges, but the Magnolia example shows why conservation must consider both habitat protection and the connections that allow populations to exchange genes.
Why tourism development creates a conservation trade-off
Visitor access can make these unusual geological landscapes better known, but development can also harm sensitive habitat and freshwater sources. Tang reports biodiversity damage near Baidong Tiankeng after development of the Dashiwei scenic area in 2018. His warning is direct: “It is clear that if the development of such tourism and promotion projects is solely based on economic interests, the unique ecological environment of karst tiankeng will be irredeemably lost.” UNESCO Courier.
That concern extends beyond the forest floor: karst landscapes are closely linked to underground water systems. Planning for tourism therefore needs to account for whole ecosystems and freshwater, not just the visible sinkhole and its visitor facilities.
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A separate example: Xingwen’s Great Funnel
The Great Funnel at Xingwen is a different site from Guangxi’s Dashiwei group. UNESCO’s International Geoscience and Geoparks Programme lists its long diameter as 650 metres and its depth as 208 metres, and describes it as “a premier place for the study of karst geology.” The UNESCO profile also describes visitor routes and a geological museum, making it an example of how a tiankeng landscape can be presented for education as well as conservation. UNESCO Xingwen profile.
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