Essentially the same as you determine salary at any other company:
In the early days there's no structure, you just get on with it. As the company grows, generally a board of directors (or non-profit: board of trustees) act as an independent governance level for the org above the exec team and (amongst other things) determine executive pay.
In the early days there's no structure, you just get on with it. As the company grows, generally a board of directors (or non-profit: board of trustees) act as an independent governance level for the org above the exec team and (amongst other things) determine executive pay.