A local rule, added to the scorecard in 2019, allows relief from interference by tree roots in the fairway
2c) If a player's ball in the fairway has interference from tree roots in the fairway, free relief is available under Rule 16.1b.
So two conditions need to be met for interference to exist in this rule;
- Your ball must be in the fairway.
- The tree root causing interference must also be in the fairway.
Rule 16.1b describes finding the reference point that avoids interference and dropping a ball within 1 club-length of that point. Our local rule doesn't resrtrict interference to lie only so relief is available if the roots interfere with your stance. Provided they're on the fairway.
Fairway isn't defined in the rules. It is defined in the dictionary though. The best I've come across is in Merriam-Webster Collegiate and Dictionary.com;
"The part of a golf course where the grass is cut short between the tees and the putting greens, exclusive of the rough, trees, and hazards."
Generally the rules have referred to the fairway as the "closely-mown area" of the course. Note 2 to old rule 25-2 (embedded ball) stated "Closely-mown area means any area of the course, including paths through the rough, cut to fairway height or less."
Warringah fairways are cut to 12mm as are green surrounds. These areas are closely-mown and are the areas where relief is available.
A question was asked about the tree short of the 7th green. If the roots of this tree are in closely-mown grass (fairway) around the tree, relief would be available. If the roots are in the bare earth around the base of the tree relief is not available. That area doesn't have grass cut to 12mm.