Cork mounts seem to be popular worldwide. Cork bark is usually thick, uneven and rough. A lot of people like it for mounting orchids. Seems to be durable for the long run.
I know Portugal has several cork tree farms, so I guess cork could be considered a natural renewable product.
If you scroll down to the Styles, Setups & Enclosures section, click on 'Growing on mounts'. There is a thread titled "Appropriate wood for mounts" with some good suggestions.
I have found that any wood that has a rough surface (and bark that does not separate easily), and that is long-lasting (doesn't rot easily) works well as a mount. As wisdomseeker noted, check out what other members of the Board have suggested. There are some inorganic materials that people also use as mounts , noted in various discussions.