Some of the places you work in are prime for these types of problems as well, not just tree-service work...Day workers, laborers, the inexperienced and those unqualified for any "organization" are always the heaviest with substance abuse problems...you would think.
In moving around the job market as much as I have, there has been alot of opportunity for meeting people of all walks and in several different fields of employ. These jobs have usually always surprised me when it came to social behaviors, both beneficial self-destructive.
As for my observations of those jobs I have held in the past, I have ranked them highest to lowest in terms of chemical use by the people I worked with:
Factory worker...alcohol and pot
K-12 teacher...alcohol and prescription drugs
Cemetery worker...alcohol, pot and stims...tied with...
...Construction/framing...alcohol, stims and pot
Graduate assistant (in association with professors)...pot and alcohol
Behavioral therapist...alcohol and stolen drugs
Map makers and research assistants...ALCOHOL
Daycare (from teacher to director)...alcohol, some pot
Truck driver...stims of any sort for days, binge drink on breaks
Security...alcohol with pot between tests
Restaurant worker (regardless of type)...alcohol/pot tie
Athletic training...alcohol, prescription drugs
Tree service...alcohol tied with pot
Painter...alcohol
That's the short of it. And only a small bit of the market...
Want to extrapolate?
Chemical use has been a part of humanity since man learned to put things in his mouth. Before that evolutionary leap however, we have all sorts of animals in the world that use various chemicals to alter their moods...look it up.
Responsibility is the key.
We have all done, and will continue to do things beyond our strengths...
...but hopefully we recognize these times through attention to such things and realize, regardless of what, where, when and why...
..."a man's got to know his limitations."