Vitality refers to the ability of a living being to adapt to environmental conditions. It includes factors such as tree nutrition, resistance to pests and diseases, and the condition of the tree crown. A tree with high vitality is usually robust and resilient and able to adapt well to changes in its environment. A tree with low vitality may have limited growth. Vitality can serve as an indicator of how likely a tree is to die.
On the Level-II sites, various parameters are collected to describe the vitality of the trees. In particular, the condition of the tree crown responds quickly to environmental influences such as drought stress.
To describe the tree crown, crown transparency is measured. This refers to the proportion of missing leaves compared to a fully foliated reference tree. Additionally, during a crown assessment, other damages and their causes are recorded.
Visible damage to the leaves caused by ozone is mainly found on forest edges. For this purpose, separate surveys are carried out near some Level II sites.

To assess tree nutrition, needles and leaves are taken from the upper tree crown and examined for their composition. The measured values are compared with tree-specific limit values to assess the condition.
Growth is measured continuously for individual trees on the Level-II sites, and for all trees in the stands at least every five years.