Two weeks collecting in caves and gorges in South China

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Very steeply sided hills characteristic of limestone karst. This limestone was first exposed ca 240 million years ago and the karst produced by the action of rain over tens of millions of years

I have just returned from collecting nettles in South West China with my great friend and colleague Professor Wei Yi-Gang and researcher Fu Long-Fei from the Guilin Botanic Gardens. For several years we have been working on documenting the nettle diversity of the limestone karst of this region, focusing on the poorly known cave-associated floras. Karst is a form of limestone which has been weathered by rain for millions of years resulting in finely divided and sharp surfaces and very steeply sided hills, small mountains and gorges. The karst where we have been working form part of a formation which runs from Myanmar, northern Thailand and Vietnam and across into southern China and includes the famous ‘stone forests’ of Yunnan and Guangxi. I am interested in karst because it is where nettles are most diverse, both in terms of genera (species groupings) and species. At a single location it may be possible to encounter eight genera and over a dozen species!

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Yuan Jiá cave in north-eastern Yunnan close to the border with Vietnam at an elevation of 1500 m, we collected five species of nettle from this cave. Click on picture to see me introducing our work outside of the cave

Because the limestone is porous it has resulted in the formation of thousands of caves whose entrances have been colonized by plants from a small group of families: nettles (Urticaceae), african violet family (Gesneriaceae), Begonias (Begoniaceae), ivy family (Araliaceae), the coffee family (Rubiaceae) together with ferns and mosses. The most diverse of these are the nettles, one group of which, Elatostema has about 1/5 of the species from this region known only from caves. As well as having very low light levels, sometimes 1/10 of 1% daylight, the caves have constant humidity and low temperatures which contrast strongly with the cave exterior. The cool air of a cave can be felt up to 20 m from the entrance, often before the cave itself can be seen. We believe that the species associated with caves have likely come from the deep shade of the forests that once dominated this area but which have since been lost to agriculture. It also possible that some of the species are relicts of a previous, cooler climate during the last ice-age. This is something that we have begun to study.

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Elatostema binatum, one of over 15 species of Elatostema known only from caves in Guangxi, Yunnan and Ghuizou. This species is unusual in bearing male flowers on young shoots, female flowers have never been seen!

Caves represent a last refuge for several hundred species in SW China and now is a time of great change as caves come under threat from tourism, agriculture, urbanization and cement production. We want to help conserve these caves and the species that they include by first documenting their diversity and distribution across SW China. This information can be disseminated within China in the hope of raising awareness and protecting individual caves. It could also be used to identify a network of protected caves which include all of these species. Professor Wei would also like to develop protocols for cultivating the species outside of caves, something that is very difficult to achieve at the moment and which could represent a vital step for their conservation.

 

 

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