Like other crops, trees grow poorly if there are too many or too few per acre. Unlike most crops though, trees live long enough and grow large enough that the optimum number per acre changes. Faster growth reduces the time required to reach harvestable size, and larger trees bring higher stumpage prices. Trees which would stagnate or die before final harvest can be utilized.
Intermediate harvests can provide periodic income and enhance fire protection and wildlife values.
Biologically Speaking Pine trees need growing space in which they compete for water, nutrients and light. With these inputs, the green needles in the crown manufacture food to increase the tree's size. The larger tree can support an expanded crown which, in turn, can produce still more food. As a result, the fastest growing trees are the most successful competitors. Since pines cannot tolerate shade, their branches thin out and die from the ground up, as the trees become crowded or overtopped.