The kind of trees that are useful for ship masts typically need to grow for serveral decades before they reach maturity. For the kind of forests that are planted, especially harvested tree farms as in real world, they dont remain in the ground for long enough to be useful for this.
Except there was a certain area of oak trees by Cambridge university that was planted for precisely this kind of harvesting (the rafters in teh main hall required very long straight timbers typical of old growth, and some trees were palnted when taht hall was built with precisely this repair in mind). But that is very much an exception.
