You use sustainable to describe the use of natural resources when this use is kept at a steady level that is not likely to damage the environment.
e.g. ...the management, conservation and sustainable development of forests...
e.g. Try to buy wood that you know has come from a sustainable source.
...the growing concern about environmental sustainability.
It wants timber to come, where possible, from sustainably managed sources.
A sustainable plan, method, or system is designed to continue at the same rate or level of activity without any problems.
e.g. The creation of an efficient and sustainable transport system is critical to the long-term future of London.
e.g. ...a sustainable recovery in consumer spending.
...doubts about the sustainability of the current economic expansion.