He also defended his record as a leader who has planted many trees.

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The disease was first observed as a new form of ash dieback in Poland in 1992, and has since spread to ash trees in many European countries.

BBC: Ash fungus genetic data released

The park has 4, 000 trees and 150, 000 perennial plants, including many golden wildflowers, which can be clearly seen scattered around canals and among the distinctive Games venues.

BBC: Orbiting views of Olympic London

Increasing trade with China is putting the trees of many countries at risk, and the insect has become well established in Chicago and New York.

BBC: By BBC Environment Correspondent Robert Pigott