On 01/11/2020 16:31:40, TimW wrote:
I am involved in a project to put some small wooden structures like
nesting boxes out in some woodland. The Desire is that they should be
100% (or at least 99%) biodegradable, so they last as long as poss but
ultimately rot away to nothing. Fixing them in trees with synthetic
ropes or straps is therefore obviously a complete no-no. So traditional
rope is required.

There's a bewildering array of different materials - coir, hemp, flax
etc and some treatments as well like tarred rope. Does anyone know what
is a good choice here for just lasting a few years out in the weather?
Is it better to have thicker rope for lasting, or just strong enough to
do the job?

What's wrong with iron nails?

Or Michael Adams' use of wooden pegs?

A rope around a tree will a variable life-time and may restrict growth
in the area affected as well as the tree finally engulfing the rope.

There are also some plastics that do degrade.