Was hier als Übermaß bezeichnet wird, kenne ich aus der Zerspantechnik als Aufmaß (das, was nachher durch Trennen, Schleifen, etc, "abgeartbeitet" wurde) und das wiederum würde ich als allowance übersetzen.

... a trim allowance of 1% is to be left on the log...

ENGLISH RESOURCE/ EXAMPLE:
"One of the more common mill specifications contained within a timber purchase agreement addresses preferred log lengths and proper trim. The log lengths preferred by a particular mill will depend on the type of product(s) that they produce. The proper trim allowance on a log ensures both that effective utilization of the tree has been made, and that the mill can produce a finished product of a given length."
"Proper trim allowance is neither too much nor too little. A log having too much trim allowance does not effectively utilize all of the tree. Overtrim may result in additional gross scale volume, but there is no benefit realized in finished product length. Quite often, a scaling deduction is made to reflect the finished product length that will be realized. A log having too little trim allowance is a costly mistake. Undertrim logs result in a finished product length that is shorter than what was intended."