The government has been accused of covering up the spread of an incurable disease that is killing Hong Kong's heritage trees and of failing to contain the infection, putting many more trees - and potentially human life - at risk.
Brown root rot or tree cancer, confirmed as the cause of historic trees falling in Nathan Road, Tsim, Sha Tsui, before and after Severe Typhoon Vicente, is said to have been officially identified in Kowloon Park in 2007.
The fungus infection has now spread across Hong Kong, but while the government told the public about the removal of individual trees since one fell on a Tsim Sha Tsim bus shelter last month, it has not disclosed the extent of the contagion, specialists say. Tsim Sha Tsui, the site of many historic trees, is the worst-hit area with at least five 'old and valuable' trees having collapsed or been removed in the past few weeks. Other affected areas include Central, Happy Valley, Lei Yue Mun, Diamond Hill and Tung Chung.
The MTR Corporation is also struggling at its nursery in Aberdeen to save two infected trees that were removed to make way for its South Island Line project.
The spread in Tsim Sha Tsui has been traced to the collapse of a third of the branches on an infected banyan in Kowloon Park - which is more than a century old, and dubbed the King of Urban Trees - in 2007.
Failure to remove infected parts and replace contaminated soil is believed to have allowed the fungus to spread by wind to other trees in the park, and to Park Lane Shopping Boulevard and the Observatory, said Lam Tak-chak, who trains arborists for the Vocational Training Council.
'In Taiwan, where preventive measures and remedies have been studied for a decade, the infected branches and soil would have been covered and burnt,' Lam said.
Lam was involved last year in observations with a team of plant pathologists from Taiwan, which has been developing means to combat the disease since a serious infection was found in its forests and plantations a decade ago. The specialists were invited to Hong Kong by the Chi Lin Nunnery in Diamond Hill.
Both tree specialist Jim Chi-yung and fungi expert Professor Chiu Siu-wai criticised the government for withholding information and for bad management.
'The spread could have been contained. The infected roots shouldn't be left exposed to the air for weeks,' Chiu said.
The disease, caused by a fungus common in Southeast Asia, eats away tree roots and weakens wood texture. It can spread via spores through air, water, soil and even humans. Due to the barely detectable symptoms and its incurable nature, trees with the disease could collapse at any time, posing great danger to pedestrians, the experts said.
They said the widespread contagion highlighted the government's ignorance of tree pathology and the failure of its tree-management office, which was set up two years ago.
A spokeswoman for the office declined to comment on why it did not inform the public of the widespread infection. It said the office's expert panel was informed about all key issues concerning the trees. She said follow-up actions were taken on the advice of Taiwanese experts, but did not specify what they were.
But Jim, a panel member, said the disease was never on its agenda. 'The government shouldn't have disclosed the information so selectively. Very often, we are only informed after a tree is removed,' he said. The office had held only four meetings with the panel in the past two years.
The chief executive of the Conservancy Association, Ken So, urged the government to set up a committee to contain the disease.
Thirteen heritage trees are infected or suspected of being infected. Of those, seven have collapsed or been removed, according to information available to the office. Some of the sites include Nathan Road, Kowloon Park, the Observatory, the former government headquarters and near the racecourse in Happy Valley.
The approximate number of trees on the government's Register of Old and Valuable Trees, which was started in 2004