Why put soap on trees?

[Mark E. Hill]

Subject: Why put soap on trees?

My wife and I just took a walk through a local "conservation" area in
Southeastern Pennsylvania. We noticed that someone had tied a bar of
SHIELD (tm) bath soap to a group of young trees and that this has
resulted in a bleached stain running down the trunk.  (I don't know what
kind of trees they were, perhaps oak).

Is this some kind treatment or a fertilizer?  What's going on?
Please cc replies to mhill at lexis.pop.upenn.edu; I am not a member of
this group.

Thanks in advance!

Mark Hill