It would be many decades, however, before iron could be used to replace timber in shipbuilding. By the eighteenth century England had not exhausted its supply of suitable domestic hardwood timber but – like the Netherlands – it imported softwood supplies. While every nation has trees and wood, ship timber is a far more limited product. The ideal woods were oak, Scots pine – but not spruce, and other large trees. Especially difficult to find were trees suitable to be masts, a crucial requirement for any sailing ship, and one that often had to be replaced after storms or wear. As suitable trees take decades to grow, in densely populated nations like England any given square meter of land could, usually, be far more valuably employed by producing foodstuffs rather than timber.