Chinese botanists say they may have an explanation for a mass die-off of plantation pine trees across the country that has baffled scientists for 50 years - it could be all in the genes.
The Pinus armandii, or Mount Hua pine, is a species native to China, and can survive in harsh conditions such as mountain cliffs. The white pine is also a symbol of long life in Chinese culture - the Taoist God of Longevity is almost always seen in paintings with a Mount Hua pine in the background.
But in the 1970s, there was a large-scale die-off of the pines in reforested areas across many provinces, and the cause has never been found.
Now, scientists at the Kunming Institute of Botany in Yunnan province say they might have the answer. Led by botanist Liu Jie, the team collected samples from pine-growing regions across China to build the country's largest database of information on the pine species.
Through genetic analysis, they found the species has three lineages - and these differences in genes mean they are not suited to the same conditions.
That explained why the trees planted during the reforestation campaign did not survive - they were not planted in their natural habitat, the scientists said in a paper published in the peer-reviewed journal Evolutionary Applications last month.
They said it also explained why there had not been a similar die-off of the pines since then.
Large-scale industrialisation began in China in the 1950s. Less than two decades later, mountains with once-thick forests had been denuded by logging, as railways, factories and new homes were built.
The deforestation problem was serious, and amid the decade-long upheaval of the Cultural Revolution, the Chinese government launched a tree-planting campaign in the late 1960s.
Although it was driven by communist revolutionary spirit, the campaign was not entirely without planning or guidance. The pines were mainly planted in areas where the same species used to grow, and the saplings were guarded and looked after by local forestry authorities.
They looked like the other Mount Hua pines growing naturally nearby, but genetic sequencing showed that even in the same mountain range, the species could have different lineages, the botanists said.
They estimated that the first lineage branched off about 9 million years ago as a large mountain range formed across central China. Some tree species could not adapt to the dramatic change of environment and perished, but the Mount Hua pine survived and thrived.
Its three lineages each have a distinct set of genes adapted to different environments, and there have been few genetic exchanges between them, according to the study.