The oak, along with the rose, is one of the great symbols of England. Reports that they face decimation as a result of a bacterial condition called Acute Oak Decline, or AOD, which makes the trees bleed to death, therefore, are bound to prompt comparisons, however illogical, in the minds of some, with the state of the country itself.
It would be strange if this were not the case, for the notion of the country as a living organism that is as prone to disease as a human body is a common one in literature. Shakespeare's Hamlet, after all, refers to Denmark as a "rotten", and not a mismanaged, state.
The superstition lingers. If all the tulips shrivelled and died suddenly, wouldn't the Dutch shiver inwardly and even fear for their country's well-being, as did the Americans when their own symbol, the bald eagle, seemed in danger of dying out?
The trick is to choose a national symbol that is truly imperishable, like a mountain, or a plant so numerous as to defy even the possibility of extinction. Surely Scotland will never be at a loss for thistles or Ireland out of shamrocks – but that's presumably what the English thought when they adopted the oak. You can never tell.