Killing a big tree isn’t easy. A good systemic disease can do it; a saw can do it, though a ton of tree and plant varieties can be regrown from roots and even cuttings, e.g. just some branch. You have to really try. In some cases, if you saw a tree down you still need to excavate the root system with it to keep the thing from eventually coming back. Figure some trees can put down roots as deep as they are tall—roots that have been known to wreck building foundations, among other things—and that is some resilience.
A parks department in Hong Kong, however, managed to kill a 400-year-old banyan tree without even trying. The tree, known as 'King Banyan', is the city’s oldest, dating back to the Qing dynasty. It stands over 70 feet tall and spreads laterally another 70 feet. King Banyan survived a 2007 typhoon that tore off a full third of the beast, but its demise comes courtesy of “improper park design.” In 1989, a portion of the park was filled in with concrete and additional soil to make it level. The concrete essentially starved and suffocated the tree, preventing oxygen, water, and nutrients from getting to its roots.
"Burying trees with compacted soil and concrete will not give you a strong tree," Hong Kong University’s Jim Chi-yung told AFP. King Banyan remains alive, but it’s slated for removal in September. The weakened and suffocating tree succumbed to a fungal infection, which now threatens other trees in the area, hence the removal. Roots suffering from the infection, brown root rot disease, typically must be incinerated to prevent the fungus from spreading.
"No other banyan tree was as old as this one, none was as big as this one," said Jim. “The whole saga is avoidable and unnecessary. It is a very sad picture."
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