We test trees for health. All green plants produce sugar (energy)in their leaves during photosynthesis. The sugar is then either used in the leaves as an energy source for growth or production of other essential materials, or it is transported via the phloem (inner bark) to other parts of the tree. 

The sugar that is not used immediately is linked together in long chains to create starch. Starch is the product the tree uses to store much of its energy reserves. By staining wood for starch, the level of the tree’s energy reserves can be estimated. This information is beneficial when making a diagnosis of the tree’s condition.