Dehradun, March 28 -- Over 17,000 trees in the forests of Dehradun are likely to be cut after being affected by Sal borer infestation, forest officials said on Friday. According to officials, nearly 15,000 sal trees (Shorea robusta) in the Dehradun forest division have been infested by the sal borer (Hoplocerambyx spinicornis), while around 5,000 trees are affected in the Kalsi forest division. In the Dehradun forest division, the infestation has been reported across multiple ranges, with officials identifying severely affected trees for felling as per the working plan. In the Kalsi division, a detailed survey has been conducted and trees have been categorised based on the extent of damage, with only the most severely affected ones marked for removal to contain the spread. The Sal borer (Hoplocerambyx spinicornis) is a wood-boring beetle that attacks sal trees by laying eggs under the bark. The emerging larvae feed on the inner tissues, disrupting the flow of nutrients and water, eventually leading to the death of the tree. Periodic outbreaks of the pest have been recorded in Sal forests across northern India, though their intensity varies. Dehradun's divisional forest officer (DFO), Neeraj Sharma, said nearly 15,000 sal trees in his division have been infested by the Sal borer. He said Sal borer larvae primarily feed on the tree's inner tissues, disrupting nutrient and water flow, which eventually causes the tree to dry out and die. "The larvae damage the inner tissues of the tree, and over a period, the tree dries up. The presence of borers is not new, but in some years, the infestation increases," he said. He added that affected trees are identified and felled after obtaining necessary permissions from the Union environment ministry. "Once the trees are felled, they are left in the forest so that the insects emerge and can be destroyed, which helps in breaking the life cycle of the pest," Sharma said. On the possible causes, Sharma said there is no single confirmed factor. "The infestation is usually noticed around the monsoon season when larvae develop. Prolonged or excessive rainfall could be one of the contributing factors," he said. Sharma further said that felling remains the only established large-scale method to control the infestation. "Research institutions such as the Forest Research Institute (FRI) have conducted experiments, but no alternative method has yet been standardised for widespread implementation," he added. DFO, Kalsi, Mayank Garg, said that around 5,000 to 5,500 trees were initially identified as affected in the division. "Out of these, about 2,000 severely affected trees will be felled as per categorisation to prevent further spread," he said. Experts said that while such infestations are not entirely new, dense monoculture plantations of Sal in the state are also considered more vulnerable to pest outbreaks. Environmentalist and forest historian Ajay Singh Rawat attributed the recurring problem to monoculture practices and called for diversification. "This will continue unless mixed forestry is adopted. Sal was extensively promoted in the Terai-Bhabhar region during the British period for railway sleepers, leading to reduced diversity," he said. "If it affects one tree, it eventually impacts the entire forest," he added....