General Advice - Wood
The Forest Stewardship Council (FSC) is a non-profit organisation which certifies wood according to strict criteria, with emphasis on sustainably harvested wood. Along with ensuring the environment is well managed and maintained, the FSC also has policies in place which help local communities. (ref) An outline of their principles can be found here, with principles ranging from allowing pesticide usage to responsibly managing forests. The logo means you can trust the wood supplied has upheld the needs of the certification. However, there are some disputes on the effectiveness of FSC, (ref), (ref) but overall, the FSC is usually a good indicator that a wood has been sourced sustainably. Other certification boards, such as the PEFC exist and advocate sustainable management of the forests.
The EU has laws and policies in place to reduce the impact of wood usage on the world, one of the biggest being FLEGT (Forest Law Enforcement, Governance and Trade) in 2003 which had the aim to reduce illegal logging and promote sustainable, legal wood. (ref)
Later in 2013, EUTR (EU Timber Regulation) was passed which made it criminal for illegal timbers to be sold on the EU market. (ref) This should mean that most wood on the EU market is fairly sustainable, however, there are examples where this is not the case. (ref)
One environmentally friendly option for garden projects is reclaimed wood, wood that has be salvaged from old buildings, boats, pallets etc. This is often less expensive than new woods and less likely to crack due to years of being dry already. Old wood is recycled, meaning that new trees will not need to be harvested, (ref) which helps save the forests and reduces the demand for fresh wood. (ref) Some rare and unique woods can be reclaimed too. Whilst this may be sustainable for forests, there is only a finite amount of reclaimed wood, meaning it will eventually run out. However, its recycled property and the fact it can, usually, be sourced locally will help the environment in the long run.
Greenpeace, an NGO with aims of a greener world, state that the demand for tropical wood is one of the main causes of illegally logged timber. This, along with deforestation leads to a loss in biodiversity and a contribution to enhanced climate change. (ref) Richard George, Head of Forests for Greenpeace UK, stated it is almost impossible for consumers to tell the difference between legal and illegal wood. (ref) This is why they advocate wood sourced from certification boards like the FSC, as it ensures a much more sustainably managed way to obtain wood. (ref)