We also need to consider the diameter of the log harvested. The recovery from a 24 inch walnut log as a percentage of useable wood (useable wood vs. sawdust, slab, etc.) is much higher than for a smaller diameter pine log half its size. For example, it would take five 12 inch pine logs (8 feet long) to equal the lumber volume sawn from one 24 inch walnut log (8 feet long). This translates into more energy in harvesting and processing to get the same lumber volume.

I do not mean to disparage pine management and use in any way. Wood in general (both hardwood and softwoods) have smaller environmental impacts than non-wood substitutes. The same cannot be said for a non-wood substitute such as steel or a short rotation non-wood substitute such as bamboo. We must look at the larger picture of natural resource management and the individual product life cycle to bring science to “green products.”

The case in favour in pine and fir at the expense of walnut is built entirely on the relative length of forest rotations (time between harvests), drawing on the mistaken assumption that shorter rotations are necessarily more environmentally benign. There is no relationship whatsoever between rate of tree growth and the sustainability of harvested wood. You’ve also got to take account of the size of the forest resource – which in the case of walnut is vast. Even the slowest growing hardwoods can be managed sustainably if the area of forest is large enough and the length of time between harvests long enough.

Analysis of U.S. government forest inventory data gathered at regular intervals over the last 60 years shows that the U.S. walnut harvest averages around 1 million m3 each year, well below the annual growth rate of 3.6 million m3. Even after harvesting, an additional 2.6 million m3 of walnut accumulates in U.S. forests every year. Even assuming that only 10% of this production is of quality suitable for a high-profile project like that in Abu Dhabi, it would take only around 90 seconds for new growth in the U.S hardwood forest to replace each cubic meter of walnut used!

Also noteworthy that nowadays many forest scientists argue that rotations in certain forests types should be lengthened so that forests provide greater biodiversity benefits and have longer to accumulate carbon before harvesting.

While there is no doubt that pine would, like Walnut, have many environmental advantages compared to alternative non-wood materials, it’s much more questionable that it would offer a better environmental option than walnut. Pine often derive from fast growing plantations, whereas walnut more often comes from managed natural forests. The latter tend to provide greater biodiversity benefits and to produce more durable wood products that need to be replaced less often.

Of course these are all complex issues – so the “green prophet” may be forgiven for failing to take them all into account. Best to rely on full blown peer-reviewed life cycle assessment – something that the US hardwood industry is also taking a lead on.