Theoretically, if PZT applied to an elastomer substrate (see attached) were affixed to trees, what might be the potential output of, say, a 50ft pine with approx. 10sq.ft. of PZT ribbon in average conditions?

In average conditions, I would expect near zero potential. Wind tends to be periodic, or very low.

What you need are at least two conditions: 1. regular wind. 2. flutter.

So, coastal areas or very large open areas (think great plains or ocean surface) with little height variation would work best. One problem is that the presence of a large number of trees will affect this.

Leaves will help with the flutter but really you need turbulent airflow.

If you were thinking to recover energy from the trees you need to remember that trees sway, oscillate, very slowly so not a good source without some mechanical conversion.

While I realize I didn’t give the answer you were looking for, I do hope this helps.