I never expected to be working in caves, that is, until I started to study nettles in Southwest China with Guangxi botanist Wei Yi-Gang. When Wei suggested that we collect in a local cave I was not hopeful. However, that first visit transported me to another world, an eerie moonscape in which plants thrived in powdery ‘soil’ and perpetual twilight. I was immediately gripped and determined to explore as many caves as possible. Over the next few years we visited over 60 caves, travelling on underground rivers, hiking across rice fields or sneaking into big tourist caves. Each time I got the same thrill from entering these strange and silent places. This has culminated in a paper just published in the scientific journal PLOS ONE.
There has been very little research on plants in caves. Having come across such a widespread and diverse flora we wanted to make sure that both botanists and cave biologists were aware of it. This is because plants growing in caves could tell us a lot about how plants adapt to extreme conditions. Also, as to how connected caves are to the surrounding landscape and each other. To do so we set out to answer a series of questions. Probably the most obvious was, are plants growing in light levels distinct to those outside? Did the species evolve in caves? Or are they survivors of a previous vegetation that at some time connected caves? And, are these plants important for conservation in the region? For example, in the restoration of the karst forests lost during the 20thC.
There are thousands of caves in Southwest China and the landscape that they helped form has long been famous in Chinese culture and art. A landscape covered in dense forest until the 20thC at which time the ‘Great leap forward’ and later the ‘Cultural revolution’ resulted in massive deforestation. Once cut, the forest has not returned but instead been replaced dry scrub. The 21stC has brought new threats from cement and tourism. The rock that forms these caves is used to make cement, now in high demand, that combined with a rapid growth in tourism has meant once untouched ‘lost worlds’ are being mined or filled with walkways, bright lights and litter.
We found that some of the plants growing in caves are surviving in very low levels of light. Levels much lower than previously known. From other cave studies we also know that daily changes in temperature and humidity are very small. There is also some suggestion from other studies that the cave atmosphere may be richer in CO2. It could be that low levels of light are being offset by more stable conditions and higher CO2 – an interesting question for future research.
We also found that whilst most of the plants we document are known from forest habitats elsewhere, 31 species are only known from caves. For reasons given in our paper we do not believe that this means that they evolved in caves but rather that they are species which were restricted to the forests lost in the 20thC.
So, it looks as if the plants that we are finding in caves are relics of forests that were lost to deforestation in the 1950s and 1970s. With a current focus on restoring these lost forests in China, these surviving populations could now become a valuable source of local plant material for restoration.
Other posts by me on this topic