Parana pine - photo by Eurico Zimbres
In terms of embodied energy the use of timber in staircases is far better than metal. However the timber should be sustainably sourced and be FSC woodmarked. One of the traditionally favourite timbers for the manufacture of closed riser staircases has been parana pine (Araucaria angustifolia) from Brazil and a fair number of timber merchants and joinery manufacturers in the UK are still claiming to be supplying sustainably sourced parana pine staircases. However the scientific literature from groups such as
Geographical Paper No.180 by J.V.M. Bittencourt , University of Reading
show the devastating manner in which parana pine has been over harvested and it is difficult to imagine how any real volume of the timber can be available on a sustainable basis.
It is on the IUCN Red List of Threatened Species as a critically endangered species.