From: fill_spector@aol.kom   
      
   Most of us associate sinkholes with frightening abysses, but in China,   
   they’re considered “heavenly” for good reason.   
      
   Far from being mouths of doom, a number of these have been discovered   
   containing pristine ancient forests.   
      
   Most recently, in August last year, cave explorers stumbled upon one of   
   these giant holes, which experts said likely contained species of small   
   animals that were unknown to science.   
      
   This extraordinary hole reportedly measures a whopping 300 metres (1,000   
   feet) in length, 150 metres (500 feet) in width and is more than 190   
   metres (630 feet deep).   
      
   It is located in China’s southwestern karst landscape and is now one of   
   30 such holes known as “tiankeng” – which translates as “heavenly   
   pits”   
   – in the region.   
      
   The reason for the trenches’ otherworldly name is that they are some of   
   the last-remaining natural refuges for ancient forests and are home to   
   species unseen anywhere else in the world.   
      
   Indeed, describing his own encounter with a tiankeng back in 2016,   
   researcher Tang Jianmin wrote: “The scene down there was stunning: an   
   underground pristine forest with no trace of human activities, with 40   
   metre-high ancient trees and a group of endangered wild plants from the   
   times of dinosaurs.”   
      
   Given their depth, very little light reaches the bottom of the tiankeng,   
   and yet, they harbour an abundance of plants.   
      
   For years it remained unclear how this was possible, but a new study,   
   published on 20 July, has revealed how a number of species have been   
   able to thrive in their depths.   
      
   The researchers found that nettles, ferns and other plants that live   
   inside them thrive off of abundant stocks of nitrogen, phosphorus,   
   potassium, calcium and magnesium.   
      
   These elements limit plant growth in other environments, where they are   
   scarce, but because they are so bountiful in the tiankeng, the plants   
   have evolved to devour them, enabling them to grow tall and benefit from   
   the trickles of sunlight that reach them.   
      
   "Plants can adapt to adverse environments by adjusting their nutrient   
   content," the study’s authors wrote, according to a translation by Live   
   Science.   
      
   "Due to the towering cliffs and steep terrain of the tiankeng, it has   
   been less disturbed by human activities.”   
      
   The deep holes host plants that favour moisture and shade, including   
   species unique to the region, the researchers add. These include modern   
   karst forest plants, such as the Nepali hog plum (Choerospondias   
   axillaris) and the Chinese rain bell (Strobilanthes cusia).   
      
   So how do these tiankeng and their forests form?   
   These remarkable sinkholes emerge when the roof of an underground   
   chamber enlarges and collapses, according to Jianmin.   
      
   Some 30 per cent of the world’s tiankeng are found in China’s Guangxi   
   Zhuang Autonomous region among its World Heritage listed karst formations.   
      
   Karst landscapes are shaped by the erosion of soluble carbonate rocks   
   such as limestone, creating features such as sinkholes, caves and   
   underground rivers.   
      
   In a piece for The UNESCO Courier, Jianmin further explains the   
   formation of these sinkholes, writing: “Karst tiankeng is a relatively   
   closed environment with high humidity, low temperature and a high   
   concentration of negative oxygen ions.   
      
   “Its bottom is connected with underground water flow, nurturing a lush   
   green oasis all year round.   
      
   “Primitive ecosystems with unique animal, plant and microbial resources   
   are formed there.”   
      
   In total, 300 tiankeng have been discovered across the globe, with China   
   home to two-thirds of them. They have also been found in Papua New   
   Guinea, Malaysia and Madagascar, Slovenia, Croatia, Italy and Spain,   
   among other countries.   
      
   Why are they important?   
   More than just a jaw-dropping natural phenomenon, these sinkholes are   
   important ecological havens.   
      
   Jianmin noted that he and fellow researchers have discovered many rare   
   and endemic plants in the tiankeng area, cementing its status as a   
   “refuge for endangered plants and primitive forest ecosystems”.   
      
   “There is also a good chance that previously unknown species will be   
   discovered in these environments,” he added.   
      
   This article was first published on 31 July 2024.   
      
   https://www.indy100.com/science-tech/tiankeng-sinkholes-china-fo   
   ests-2671238574   
      
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