What does a sick tree look like?
In the course of vegetation inventories, we note the health status of each individual tree, classifying it as "healthy", "sick", "dead", or "snag". A tree is classified as "sick" if it is determined by the observer that it is not likely to survive another 5 years or so. Usually this is determined by an assessment of the size of the living crown relative to the size of the bole. A tree with a large bole and few leaves left in the canopy will not be able to produce enough nourishment for maintenance of all the tree's tissues, and it will gradually die. Generally a sick tree also has yellowing leaves and some dead branches in the canopy, similar to the tree in this photo. A sick tree is, of course, still considered to be a "live" tree for our calculation purposes (and sick trees do sometimes get better!).
A tree is considered
"dead" if it has no leaves, but still retains most of its upper branches.
A "snag" is defined as a tree with no leaves and virtually no upper branches--basically
only the bole remains standing. In the left photo below, a dead tree
is pictured in the center and a snag with one small branch is in the foreground
to the left. In the right photo, a snag is pictured in the center.
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