As told by Alexander Rose, Director of New College.
“New College at Oxford was founded in the late 1300s. The great dining hall was built with enormous oak beams. In the late 1800s, they discovered that there were beetles in the beams. Dismay ensued — no one knew where they’d find oak trees big enough to replace the lost beams. Someone had the bright idea to summon the college forester. The forester does have such oaks. It turns out that a stand had been planted and set aside when the great hall was built and while everyone at the college had forgotten about them, the forestry people had been under strict orders passed down for 500 years.”

Alternatively:
The Swedish military was confronting a resource problem of its own. Demand for warships meant that there was a need for 150 year old oak trees. Foreseeing a shortage, the Navy began planting on Visingsö island. The trees came of age in the 1980s, when warships were made of steel.