[microcolonel]

> So they assume that the average bit of timber lasts thirty years before giving up its carbon, and only about one in six lasts longer than 45 years. I suppose the lifecycle of wooden manufactured items tends to end with them being burnt when they're worn out.

That seems like a pretty bizarre set of assumptions. Wood doesn't just disappear in 45 years unless you leave it in the open untreated.

[twic]

As i wrote in the paragraph you quote, my assumption is that this models wooden items being burnt at the end of their useful lives.

But hey, don't take my word for it - in the paper, that bit references this:

Penman J, Gytarsky M, Hiraishi T, Krug T. Good practice guidance for land use, land-use change and forestry. Intergovernmental Panel on Climate Change (IPCC), chapter 3, Appendix 3.A.1.3. UNEP; 2003. p. 268–70.

Which you can read here:

https://www.ipcc-nggip.iges.or.jp/public/gpglulucf/gpglulucf...

https://www.ipcc-nggip.iges.or.jp/public/gpglulucf/gpglulucf...

So dive into the gory details of harvested wood products, and the basis for their future methodological development to your heart's content!