Which method can encourage more aggressive growth in the upper crown of a young sapling?

Removing or shortening branches on the lower portion of a young sapling creates a phenomenon known as "crown release," which allows more light and resources to be directed toward the upper crown. This promotes more vigorous growth in that area by reducing competition for light and nutrients from lower branches. When lower branches are removed or shortened, the sapling can allocate more energy towards vertical growth, encouraging the upper crown to expand and develop more rapidly.

This method is particularly effective for young trees since they are still establishing their structure and can benefit greatly from adjustments to their form. By prioritizing growth in the upper crown, the overall shape and health of the tree can improve, helping it develop a strong central leader—a crucial aspect for longevity and stability.

In contrast, while increasing watering frequency or applying fertilizer might contribute to a tree's overall health, these methods would not specifically direct resources to the upper crown. Reducing sunlight exposure would hinder growth rather than encourage it.