Context: In the early 18 hundreds the Napoleonic was on going. Denmark was at the time a naval force to be reckoned with. Although not exactly a threat to the British fleet, the British were worried that Denmark would be occupied by the French, which could potentially boost the size of the French fleet. This would in turn give the French a fleet that would allow them to take the British fleet head on. As a preemptive measure the British asked Denmark to hand over the majority of they vessels. However Denmark wanted to remain neutral in the war, and giving a large chunk of ships to one side would definitely have made the French upset. Thus they denied the British request. Following this the British decided to destroy the potential threat. This ended with the 1807 bombardment of Copenhagen. The Danish fought back, but in the end handed over a bunch of ships, after they had also lost a handful.
Oak trees are the common tree for construction of large ships, in the age of sails. Oak trees are however only harvested after around 120 years of growing and maintenance. And the Danes had no were near the amount of forest or trees at hand to rebuild the navy. That's why they planted the trees that a now known as "flåde eg" or "the fleets oak"
That's a question that enough other people have asked that the Naval History and Heritage Command Detachment Boston has answered with an estimate of 85-90% of the wood has been replaced.