Oakstead has a comprehensive, thorough assessment process for tree health. It starts with a conversation about the history of the site and the tree.
The assessment is then split into 2 parts; an “abiotic” assessment, and a “biotic” assessment. Generally we look at the abiotic side first. Abiotic factors that we consider are things that are non-living; access to light, soil composition, drainage, toxicity, mechanical damage, etc. Then we look for evidence of insects and disease (biotic). Most insects and diseases exist at low levels all the time but most trees can resist them to some extent and will be fine if they are, otherwise healthy. But if a tree is weakened by one or more abiotic issues, it may become more vulnerable to biotic problems.