Which factor should be avoided when pruning a newly planted tree?

Pruning healthy branches in a newly planted tree should be avoided because it can impede the tree's ability to establish a robust root system and overall health. During the early stages of a tree's development, it is essential to allow the tree to focus its energy on establishing roots and acclimating to its new environment. Healthy branches contribute to photosynthesis, which generates the energy needed for growth. Removing them can lead to weakening the tree and potentially stunting its overall growth.

In the context of the other options, pruning lateral branches can be necessary to shape the tree and encourage a strong central leader. Pruning broken or damaged limbs is often recommended to prevent disease and promote healthy growth. Pruning at the base is sometimes appropriate for removing low limbs that are not needed, which might enhance a tree's form and accessibility but should be done with caution. Thus, keeping healthy branches intact is crucial for the tree's immediate establishment and long-term health.