What makes a material sustainable? The best way to consider a material is by assessing it's entire life cycle. This includes the energy that has been put in to the prouduction and design, right through to the transport and installation. But what happens next is just as important. Consider how long the material is going to last. When you are finished with it, can it be recycled, down-cycled etc?
For finished visible areas, sustainably forested Australian hardwoods are you best choice. Timber has low embodied energy and the timber industry in Australia is regulated to a higher level than the places we import timber from currently.For outdoor use you should be using class 1 or 2 hardwoods. This roughly tells us the natural durability of the timber and gives us an idea of how long the timber will last. The lower the number the longer the life. Some regularly available class 1 timbers include: Cypress and Ironbark. Class 2 timbers often stocked are: Blackbutt, Spotted Gum and River Red Gum and Yellow Stringy-bark. Timbers to avaoid are: Merbau and Teak. They originate in India, Indonesia, Malaysia and Burma and it is tricky to ascertain the embodied energy and the methods used in their harvesting. It is easier to stick to the Australian hardwoods.
Alternate surfaces with low embodied energy
Toppings and granitic sand are great in the landscape due to their low embodied energy. They will not suit all applications but are fantastic for low use areas.