Maturity

• The first and most significant difference between a full-grown tree and a sapling is maturity. A mature tree has a great deal of old growth, a large root system from which to drink and take nutrition and is designed with reproduction in mind with no further stages of growth to expend energy upon. Saplings, conversely, are growing fast but have not yet grown a large network of roots and cannot reproduce. This intermittent stage between seedling and tree is a period of fast growth for the sapling, as it works to establish itself in its environment before other saplings, shrubs and plants can take all the resources.
  
  

Infestation

• While saplings are smaller and made from new growth principally, mature trees have a great deal of old growth as well as new leaves and branches that increase the plant's capability to photosynthesize. These differences affect an insect's preference when choosing a plant to infest and feed on. According to a 2001 study conducted by Yves Basset of the IBISCA international research project, leaf-eating and sap-sucking insects were 2.5 times as likely to feed on the leaves of a mature plant as those of a sapling.
  
  

Photosynthesis Rate

• The rate of photosynthesis is also a key difference between mature trees and saplings. While plants have more leaves in maturity than they do when they are saplings, leaves photosynthesize more when plants are saplings, according to the results of a 2002 study by Sean C. Thomas of the University of Toronto and William E. Winner of Oregon State University. This study showed that, while mature trees photosynthesized more energy on the whole, they did so less efficiently than saplings in the same area.
  
  

Resistance

• While mature plants may photosynthesize less and suffer more from infestation, they are also capable of resisting weather and other factors far better than saplings. The well-established root system of a mature tree has more places to look for water and nutrients. Meanwhile, above-ground areas of the tree such as the trunk and the branches are better able to withstand strong winds and even infestation because of their size and hardness.