Leaves perform two vital functions for trees. They produce sugars by photosynthesis and they allow for the distribution of water through transpiration.
Photosynthesis is a process by which CO2 and water are combined with sunlight and a pigment called chlorophyll. The chemical reactions result in the production of sugars which
provide energy to the tree. The leaves use some of this energy, but the majority is transported, in the form of sugar solutions, to other parts of the tree that require it.
Transpiration, or water loss, also takes place in the leaves. As this occurs, water is drawn up from the roots through the vascular system to replace lost moisture.