This research examined three types of moso bamboo stands: pure moso bamboo forest prior to understory vegetation succession, understory vegetation succession formed by harvesting bamboo timber once every 6–8 years over periods of 9 and 21 years, and pure forest (control). We investigated the morphological quality of the main and lateral branches and leaves, efficiency of pumping and spreading, and biomass anisotropic growth relationship of 1st- and 2nd-degree bamboo. Results showed that: (1) With the succession of understory vegetation, the primary morphological and quality traits of the main branch leaves of 1st-degree bamboo showed a downward trend, while 2nd-degree bamboo showed a significant “V”-shaped change; (2) Length and slenderness of the main and lateral branches of 1st- and 2nd-degree bamboo increased significantly, while branch diameter, branch dry matter content, and branch dry weight showed an inverted “V”-shaped or increasing trend, with the changes in branch morphology being more pronounced than those in branch quality; (3) The leaf spreading efficiency index of 1st-degree bamboo showed a “V”-shaped change, whereas that of the main and lateral branches of 2nd-degree bamboo decreased significantly, with the Huber value increasing significantly; (4) Within a certain succession period, the biomass growth relationship of the main and lateral branches of the standing bamboo transitioned from isochronous to anisotropic growth, then reverted to isochronous growth. Thus, understory vegetation succession exhibited an important effect on the morphological quality of bamboo branches and leaves, efficiency of branching and spreading, and relationship between anisotropic growth and branch and leaf biomass in moso bamboo forests. Notably, leaves tended to be smaller and branches slenderer. Furthermore, successional age and age of standing bamboo had obvious effects, mainly on the leaves of the main branches, with 1st-degree bamboo being more sensitive than 2nd-degree bamboo. Hence, during the succession process, bamboo invests more resources in branch growth to enhance competition for spatial resources.